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application note tea2260/tea2261 high performance driver circuits for s.m.p.s AN376/0694 summary page i introduction .................................... ................... 2 i.1 master slave mode. ................................................ 2 i.2 burst mode . . . . . . . . . . . . . . . . . ....................... ................ 2 i.3 operation of master slave power supply in tv application . . . . . . . . 2 i.4 secondary regulation .......................... ................... 6 i.5 primary regulation . . . . . . . ......................................... 8 ii circuit description ................................................ 9 ii.1 voltage reference and internal v cc generation. . . . . . . . . . . . . . . . . . . 10 ii.2 oscillator . . . ............. ......................................... 10 ii.3 error amplifier . . . . . . . ...... .................... ................... 12 ii.4 pulse width modulator . . . . . . . . . . . . . . . ............................. 12 ii.5 soft start operation . . . . . ......................................... 13 ii.6 burst generation in stand by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 ii.7 islogic............................................................. 14 ii.8 safety functions : differences between tea2260 and tea2261. . . . . . . 15 ii.8.1 i max . . . . . . . . . . . . . . . . . . . . . . . . . ....................................... 16 ii.8.1.1. first threshold vim1 . . . . . . . . . ......................................... 17 ii.8.1.2. second threshold vim2 for tea2260 . .................................... 18 ii.8.1.3. second threshold vim2 for tea2261 . .................................... 18 ii.8.2 logical block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 18 ii.8.2.1. logical block for tea2260 . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 18 ii.8.2.2. logical block for tea2261 . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 19 ii.9 output stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 19 iii tv application 120w 22o vac 16khz synchronized ................... 20 iii.1 characteristics of application . . . . . . . ............................. 20 iii.2 calculation of external components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 iii.2.1 transformer calculation. . . . . . . . . . . ....................................... 21 iii.2.1.1 transformer specification . . . . . . . ....................... ................ 22 iii.2.2 switching transistor and its base drive . . . . . . . . . ............................. 22 iii.2.2.1 current limit calculation . . . .......................... ................... 22 iii.2.2.2 snubber network . . . . . . . . .......................... ................... 23 iii.2.2.3 base drive . . . . . . . . . . . . . . . . . . . ....................... ................ 24 iii.2.3 oscillator frequency . . . . . . . .......................... ................... 25 iii.2.4 regulation loop . ....................................................... 25 iii.2.5 overload capacitor . . . . . . . . . . . . ......................................... 26 iii.2.6 soft start capacitor . . . . . ............................. ................... 26 iii.2.7 feedback voltage transformer . . . . . ....................................... 26 iii.2.8 start up resistor. . . . . . . . . . . . . . . . . ....................................... 27 iii.2.9 high voltage filtering capacitor . . . . . . . . . . . . . . . ............................. 28 iii.3 electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 29 1/33
summary (continued) page iv tv application 140w 220 vac 32khz synchronized .................... 32 iv.1 application characteristics . . . . . . . . . . . . . .......... ................ 32 iv.2 transformer characteristics . .................... ................ 32 iv.3 electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 33 v tv application 110w 220 vac 40khz regulated by optocoupler ...... 34 v.1 frequency soft start . . . . ......................................... 34 v.2 application characteristics . . . . . . . . . . . . . .......... ................ 34 v.3 transformer specification . . . . . . . . . . . ............................. 34 v.4 electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 35 i - introduction the tea2260/61 is an integrated circuit able to drive a bipolar transistor directly with an output base current up to 1.2a. so the tea 2260/61 covers a wide range of appli- cation from 80w to more than 200w with all safety requirements respected. the high performances of the regulation loop pro- vide a very low output power due to an automatic burst mode. the tea2260/61 can be used in a master slave structure, in a primary regula- tion or a secondary regulation. the tea 2260/61 is very flexible and high perform- ance device with a very large applications field. the only difference between tea2260 and tea2261 concerns security functions (see para- graph ii.8) i.1 - master slave mode (figure 1) in this configuration the master circuit located on the secondary side, generates pwm pulses used for outputvoltage regulation. these pulses are sent via a feedback transformer to the slave circuit (figure 1). in this mode of operation, the falling edge of the pwm signal may be synchronized with an external signal. by this way the switching off time of the power transistor, which generates lot of parasites, can be synchronized on the line flyback signal in tv applications. an other advantag e of the master slave structure is to have a very good regulation not depending of the coupling between transformer primary and secondary windings, which allows the use of low cost switch mode transformers. i.2 - burst mode (figure 2) during start-up and stand-by phases, no regulation pulses are provided by the master circuit to the slave circuit. the slave circuit operates in primary regulation mode. when the output power is very low the burst mode is automatically used. this operating mode of the smps effectively pro- vides a very low output power with a high efficiency. the tea2260/61 generates bursts with a period varying as a function of the output power. thus the output power in burst mode can varied in a wide range from 1w to more than 30w. i.3 - operation of master slave power supply in tv application the system architecture generally employed is de- picted in figure 3. on the secondary side a micro controller is connected to the remote control re- ceiver which generates control signal for the stand- by and normal modes of operation (figure 4). - in stand-by mode, the device power consumption is very low (few watts). the master circuit does not send pulses and hence the slave circuit works in primary regulation and burst mode. - in the normal mode, the master circuit provides the pwm signal required for regulation purposes. this is called master slave mode. the mas- ter circuit can be simultaneously synchronized with the line flyback signal. - power supply start-up. as soon as the v cc (start) threshold is reached, the slave circuit starts in continuous mode and primary regulation as long as the nominal output voltages are not reached. after this start-up phase the microcontroller holds the tv set in stand-by mode or either in normal mode. high performance driver circuits for s.m.p.s 2/33
slave circuit master circuit sync. pulses pulse input base current pwm signal 376-01.eps figure 1 burst period typ 30ms ~ ~ collector current envelop detail of one burst switching period 376-02.eps figure 2 : burst mode operation high performance driver circuits for s.m.p.s 3/33
audio output stage scanning device tea5170 mains input r c tea2260/61 voltage regulator m p infra-red receiver muting control remote stand-by remote stand-by synchronization v cc 2 p p 1 v cc 2 1 p : output voltage adjustement in normal mode p : output voltage adjustement in stand-by small signal primary ground power primary ground secondary ground (isolated from mains) pwm 376-03.eps figure 3 : tv application system diagram high performance driver circuits for s.m.p.s 4/33
start-up stand-by normal operation stand-by t t t t t t 1 1 2 stand-by control voltage m p supply voltage 2 1 tea5170 output voltage envelop output voltage collector current envelop v v cc cc(start) cc(stop) 12 t 2 tea2260/61 v voltage * t and t : commands issued by m p 376-04.eps figure 4 : system description (waveforms) high performance driver circuits for s.m.p.s 5/33
i.4 - secondary regulation (figures 5 and 6) in this configuration the tea2260/61 provides the regulation through an optocoupler to ensure good accuracy. the advantage of this configuration is the avaibility of a large range of output power variation (e.g 1w to 110w). this feature is due to the automatic burst mode (see paragraph ii.6). the structure in a tv set is simpler than the master slave structure because the power supply switches from normal mode to burst mode automatically as a function of the output power. audio output stage scanning device mains input r c tea2260/61 voltage regulator m p infra-red receiver muting control remote stand-by v cc p v cc p : output voltage adjustement small signal primary ground power primary ground secondary ground(isolated from mains) 376-05.eps figure 5 : tv application system diagram high performance driver circuits for s.m.p.s 6/33
start-up stand-by normal operation stand-by t t t t t t 1 1 m p supply voltage output voltage collector current envelop v v cc cc(start) cc(stop) 12 t 2 tea2260/61 v voltage * t and t : commands issued by m p stand-by voltage envelop 376-06.eps figure 6 : system description (waveforms) high performance driver circuits for s.m.p.s 7/33
i.5 - primary regulation (figure 7) in this configuration the tea2260/61 provides the regulation through an auxilliary winding. this structure is very simple but the accuracy de- pends on the coupling between the transformer primary and secondary winding. due to the automatic burst mode the output power can vary in a large range. audio output stage scanning device mains input r c tea2260/61 voltage regulator m p infra-red receiver muting control remote stand-by v cc p v cc p : output voltage adjustement small signal primary ground power primary ground secondary ground (isolated from mains) 376-07.eps figure 7 : tv application system diagram high performance driver circuits for s.m.p.s 8/33
ii - circuit description figure 8 shows the integrated functions. 7 6 16 15 14 3 8 2 1 10 11 9 45 12 13 error ampliflier internal bias modulator logic automatic burst generation is logic logic processor v monitoring cc ref v (2.49v) positive output stage negative output stage repetitive overload protection current limitation secondary pulse 0.15v 0.6v 2.55v 0.9v 10 m a 45 m a primary pulses regulation pulses overvoltage protection 15.7v demagnetization sensing modulators v 2.49v ref 7.4v 10.3v oscillator on(max.) cc v + 1.2a (max.) e sv v+ cc out gnd i max c 2 in is cc 10 0 r + - + - + - + - + - + - + - + - t (60%) soft-start -1 -2a (max.) 376-08.eps figure 8 high performance driver circuits for s.m.p.s 9/33
the circuit contains 8 blocks : - voltage reference and internal v cc generation. - rc oscillator - error amplifier - pulse width modulator (pwm) - ois logico for transformer demagnetization check- ing. - current limitation sub-unit (imax) - logical block. - output stage. ii.1 - voltage reference and internal v cc gen- eration (figure 9) this block generates a 2.5v typ. voltage reference valid as soon as v cc exceeds 4v. it is not directly accessible externally but is transmitted to other blocks of the circuit. this block also generates an internal regulated v cc ,v cc(int) , the nominal value of which is 5v. v cc(int) supplies the circuit when vcc is higher than v cc(start) (10.3v typ.). this allows the circuit to achieve a good external v cc rejection, and to provide high performance even with large v cc supply voltage variations. this block also generates initialization and control signals for the logical block. it also contains the v cc(max.) comparator (typ threshold 15.7v). ii.2 - oscillator (figures 10 and 11) the oscillator determines the switching frequency in primary regulation mode. two external compo- nents are required : a resistor r o and a capacitor c o . the oscillator generates a sawtooth signal, which is available on pin 10. 376-09.eps figure 9 : voltage reference block principle 376-10.eps figure 10 : operating principle high performance driver circuits for s.m.p.s 10/33
c o capacitor is charged with a constant current. the current is fixed by r o which is supplied by voltage v ref . i ch = 2.5 r o when the voltage across c o reaches 2 3 xv ccint ( typ 3.33v ) , q transistor conducts and c o is quickly discharged into an 2k w (typ) internal resistor. when the voltage reaches 1/3 x v ccint (typ 1.66v), the discharge is stopped, and the linear charge starts again. theoretical values of t,t 1 and t 2 as function of r o and c o : t=c o (0.69 x r o + 1380) t 1 =r o xc o x 0.69 t 2 =c o x 2000 x 0.69 = c o x 1380 due to the time response of comparators and normal spread on thresholds values, the real val- ues oft 1 and t 2 may be slightly different, compared with these theoretical values (see figure 12). 376-11.eps figure 11 : sawtooth available accross c o 376-12.eps figure 12 : frequency as a function of r o and c o high performance driver circuits for s.m.p.s 11/33
376-14a.eps / 376-14b.eps figure 14 ii.3 - error amplifier (figure 13) it is made of an operational amplifier. the open loop gain is typically 75db. the unity gain frequency is 550khz (typ). an internal protection limits the out- put current (pin 7) at 2ma in case of shorted to ground. 376-13.eps figure 13 output and inverting input are accessible thus giving high flexibility in use. the non-inverting input is not accessible and is internally connected to v ref (or0.9v ref in burst mode - see paragraphii.6) before driving the pulse width modulator (pwm) and in order to get the appropriate phase, the error amplifier is followed by an inverter. ii.4 - pulse width modulator (pwm) (figure 14) the pulse width modulator consists of a compara- tor fed by the output signal of the error amplifier and the oscillator output. its output is used to generate conduction signal. the tea2260/61 actually integrates two pwm : - a main pwm generates a regulation signal ( ) by comparing the error signal (inverted) and the sawtooth. - an auxiliary pwm generates a maximum duty cycle conduction signal ( b ), by comparing the sawtooth with an internal fixed voltage. further- more, during the starting phase of the smps, in association with an external capacitor, this pwm generates increasing duty cycle, thus allowing a osofto start-up. - a logic oando between signals ( ) and ( b ) pro- vides the primary regulator output signal t a . high performance driver circuits for s.m.p.s 12/33
376-16.eps figure 16 : c1 voltage (pin 9) 376-15.eps figure 15 ii.5 - soft start operation (figure 16) from t 1 to t 2 , there is no output pulse (pin 14) and c 1 is charged by a 180 m a current (typically). when c 1 voltage reaches 1.5v (typically), output pulses appear and the charge current of c 1 is divided by 20 (9 m a typically), then the duty cycle increases progressively. when c 1 voltage reaches 2.7v (typi- cally), the soft-starting device ceases to limit the duty cycle, which may reach 60%. under established conditions c 1 voltage is charged to 3.1v (typically) ii.6 - burst generation in stand by (primary regulation mode) when the smps output power becomes very low, the duty cycle of the switching transistor conduction becomes also very low. in order to transmit a low average power, while ensuring correct switching conditions to the power transistor, a obursto system is used for energy transmission in stand by mode. principle for a medium output power (e.g. more than 10w), the voltage reference is applied to the non- invert- ing input of the error amplifier. when output power decreases as the minimum conducting time of the power transistor is reached, the output voltage tends to increase. consequently the error signal applied to the pwm becomes higher than the saw- tooth. this is detected by a special logic and the voltage applied to the non inverting input becomes v ref = 0.9 x 2.5 = 2.25v typically. consequently the regulation loop is in an overvol- tage equivalent state and the output pulses disap- pear. the output voltage decreases and when it reaches a value near 0.9 times the normal regula- tion value , the voltage applied to the non inverting input is switched again to the normal value v ref = 2.5v. pulses applied to the power transistor reappear, the output voltage increases again, and so on... a relaxation operation is obtained, gener- ating the burst. futhermore, to avoid a current peak at the begin- ning of each burst, the soft-start is used at this instant. advantages of this method - improved power supply efficiency compared with traditional systems, for low power transmission. - automatic burst-mode continuous mode transi- tion, as a function of the output power. - high stand-by power range. - burst frequency and duty cycle adjustable with external components to the circuit. high performance driver circuits for s.m.p.s 13/33
376-17.eps figure 17 : is logic principle schematic 376-18.eps figure 18 ii.7 - is logic (figure 17) during the transition from the ostand-byo mode to the onormal operatingo mode, conduction pulses generated by the secondary regulator occur con- currently with those from the primary regulator. these pulses are non-synchronous and this may be dangerous for the switching transistor. for ex- ample if the transistor is switched-on again during the overvoltage phase, just after switching-off, the fbsoa may not be respected and the transistor damaged. to solve this problem a special arrangementcheck- ing the magnetization state of the power trans- former is used. the aim of the is logic is therefore to monitor the primary regulation pulses (ta) and the secondary regulation pulses (pin 2), and to deliver a signal tb compatible with the power transistor safety require- ments. the is logic block comprises mainly two d flip- flops. when a conduction signal arrives, the correspond- ing flip-flop is set in order to inhibit a conduction signal coming from the other regulation loop. both flip-flops are reset by the negative edge of the signal applied to the demagnetizationsensinginput (is pin 1). note : the demagnetization checking device just described is only active when there are concur- rently primary and secondary pulses, which in prac- tice only occurs during the transient phase from stand-by mode to normal mode. when the power supply is in primary regulation mode or in secondary regulationmode, the demag- netization checking function is not activated. high performance driver circuits for s.m.p.s 14/33
ii.8 - safety functions : differences between tea2260 and tea2261 tea2260 concerning the safety functions, v cc (max) (over- voltage detection) vim1, vim2 (overcurrent detec- tion) the tea2260 uses an internal counter which is incremented each time v cc stop is reached (after fault detection) and try to restart. after 3 restarts with fault detection the power supply stops. but in certain cases where the tv set is supplied for a long time, without swich off, the power supply could stop (cases of tube flashes). in this case it is necessary to switch off the tv set and swich on again to reset the internal counter. tea2261 the safety detections are similar to tea2260 for v cc (max) (overvoltage detection) vim1, vim2 (overcurrent detection),but each time a fault detec- tion is operating the c 2 capacitor is loaded step by step up to 2.6v, (case of long duration fault detec- tion) and the power supply stpos. to discharge c 2 capacitor it is necessary to switch off the tv set and to switch on again and the power supply starts up. s.m.p.s. starting first threshold reached vim1 pulse by pulse current limiting c charged 2 v < 2.6v c2 cc v max reached 2 s.m.p.s. stopping v stop reached n=n+1 cc normal operating c discharged restart number = 3 definitive stopping reset c discharged 2 n n y n n y y y n y y n second threshold reached vim2 376-19.eps figure 19 : tea2260 safety functions flowchart high performance driver circuits for s.m.p.s 15/33
s.m.p.s. starting first threshold reached vim1 2 v < 2.6v c2 cc v max reached 2 normal operating c discharged definitive stopping n n y n n y y y n y pulse by pulse current limiting c charged 2 c charged s.m.p.s. stopped v < 2.6v c2 y reset c discharged 2 n second threshold reached vim2 376-20.eps figure 20 : tea2261 safety functions flowchart ii.8.1. i max (power transistor current limitation) the current is measured by means of a resistor inserted in the emitter of the power transistor. the voltage obtained is applied on pin 3 of the tea2260/61. the current limitation device of the tea2260/61 is a double threshold device. for the first threshold, there isno difference between the two devices,only for the second threshold. 376-21.eps figure 21 high performance driver circuits for s.m.p.s 16/33
ii.8.1.1 - first threshold : vim1 (typical value) 376-22.eps figure 22 : current limitation schematic principle. first threshold part. two actions are carried out when the first threshold is reached - the power transistor is switched-off (pulse by pulse limitation). a new conduction pulse is nec- essary to switch-on again. -the c 2 capacitor, which is continuously dis- charged by idisch current (10 m a typically), is charged by the current ich - i disch (45 m a-10 m a=35 m a typically), until the next conduction pulse. the capacitor c 2 is charged as long as an output overload is triggering the first current limitation threshold. when the voltage across c 2 reaches the threshold v c2 (typically 2.55v), output pulses (pin 14) are inhibited and the smps is stopped. a restart may be obtained by decreasing vcc under the v cc(stop) threshold to reset the ic. if the output overload disappears before the volt- age across c 2 reaches v c2 , the capacitor is dis- charged and the power supply is not turned off. due to this feature, a transient output overload is tolerated, depending on the value of c 2 (see iii.2.5). 376-23.eps figure 23 : example of first current limitation threshold triggering high performance driver circuits for s.m.p.s 17/33
376-24.eps figure 24 : tea2260 simplified logical block diagram ii.8.1.2 - second current limitation threshold (vim2) for tea2260 in case of hard overload or short circuit, despite the pulse by pulse current limitation operation, the current in the power transistor continues to in- crease. if the second threshold vim2 is reached, the power supply is immediately turned off and the internal counter is incremented. after 3 restarts, the power supply is definitively stopped.restart is ob- tained by decreasing v cc below v cc(stop) , as in the case of stopping due to the repetitive overload protection triggering. ii.8.1.3 - second current limitation threshold (vim2) for tea2261 for this device, if the second threshold is reached, the power supply is turned off, c 2 is charged and a new start-up is authorized only if v c2 < 2.6v. ii.8.2 - logical block this block receives the safety signals coming from different blocks and inhibits the conduction signals when necessary. ii.8.2.1 - logical block for tea2260 tb is the conduction signal (primary or secondary)coming from the is logical block. tc is the conduction signal transmitted to the output stage. i 1 is the output signal of the first current limitation threshold comparator. it is memorized by the flip-flop b1. i 2 is the output signal of the second current limitation threshold comparator v c2 is the output signal of the comparator checking the voltage across c2. v cc (max.) is the signal coming from v cc checking comparator. these three signals v c2 ,i 2 , vcc (max) are memo- rized by b 2 . in case of b 2 flip-flop setting (i 2 or v c2 or vcc (max ) defect) the current consumption on v cc increases. this function allows to decrease the vcc voltage until v cc(stop ). after this the current consumption on vcc decreases to i cc(start) and a new start up is enabled. the v cc(off) signal comes from the comparator checking v cc . a counter counts the number of v cc(off) establishment. after four attempted starts of the power supply the output of the circuit is inhibited. to reset the circuit it is necessary to decrease v cc below 5.5v typically. in practice this means that the power supply has to be discon- nected from the mains. high performance driver circuits for s.m.p.s 18/33
ii.8.2.2 - logical block for tea2261 or or and tc 2.6v 8 reset 2 i t 2 c b i 1 v cc (max.) v cc (off) s rq q s r q q q s r 376-25.eps figure 25 v cc (off) is a signal coming from a comparator checking v cc . when v cc >v cc (stop),v ce (off) is high. v cc (max) is a signal coming from a comparator checking v cc . when v cc >v cc (max),v cc (max) is high. i 1 is a signal coming from the first current limitation threshold comparator. when i max xr shunt > vim1, i 1 is high. i 2 is a signal coming from the second current limi- tation threshold comparator. when i max xr shunt > vim2,i 2 is high. tb is the conduction signal coming from the error ampliflier system. tc is the output signal transmitted to the output stage. ii.9 - output stage the output stage is made of a push-pull configura- tion : the upper transistor is used for power transis- tor conduction and the lower transistor for power transistor switch-off. a capacitive coupling is recommanded in order to provide a sufficient negative base current through the power transistor . 376-26.eps figure 26 high performance driver circuits for s.m.p.s 19/33
376-27.eps figure 27 : typical voltage drops of output transistor versus current important remark : due to the internal output stage structure, the output voltage (pin 14) must never exceed 5v. this condition is respected when a bipolar transistor is driven. note that power-mos transistor drive is not possi- ble with the tea2260/61. iii - tv application 120w - 220 vac - 16khz synchronized on horizontal deflec- tion frequency general structure and operational features of this power supply were outlined in section i. the details covered below apply to a power supply application using the master circuit tea5170. (refer to tea5170 data sheet and tea5170 appli- cation note oan088o for further details). iii.1 - characteristics of application - discontinuous mode flyback smps - standby function using the burst mode of tea2260/61 - switching frequency - normal mode : 15.625 khz (synchronized on horizontal deflection frequency) - standby mode : about 16khz - nominal mains voltage : 220 vac mains voltage range : 170 vac to 270 vac - nominal output power : 120w - output power range in normal mode 14w < p o < 120w - output power range in standby mode 1w < p o < 25w - efficiency - normal mode : 85% (under nominal conditions) - stand by mode : 45% - regulation performance on high voltage output : 140 vdc - 0.3% versus mains variations of 170 vac to 270 vac (p out : 120w) - 0.5% versus load variations of 14w to 120w (v in = 220 vac) - overload protection and complete shut down af- ter a predetermined time interval. - short circuit protection. - open load protection by output overvoltage de- tection - complete power supply shut-down after 3 re- starts resulting in the detectionof a fault condition. - complete power supply shut-down when v c2 reaches 2.6v for tea2261. iii.2 - calculation of external components also refer to tea5170 application note oan-088o for calculation methods applicable to other power supply components. the external components to tea2260/61 deter- mine the following parameters : - operating frequency in primary regulation - minimum conduction time in primary regulation - soft start duration - overload duration - error amplifier gain and stand-by output voltage - base drive of the switching transistor - primary current limitation ideal values - free running frequency in stand-by mode : 16khz -ton (min) duration : 1 m s - soft start duration : 30ms - maximum overload duration : 40ms - error amplifier gain : 15 - maximum primary current depends on the trans- former specifications high performance driver circuits for s.m.p.s 20/33
iii.2.1 - transformer calculation the following important features must be consid- ered to calculate the specifications of the trans- former : - maximum output power : 120w - minimum input voltage : - 220 vac - 20% vin(min) = 210 vdc with 40v ripple on the high voltage filtering capacitor - switching frequency : 15.625khz - maximum duty cycle : 0.45 - output voltages : + 140v - 0.6a + 14v - 0.5a + 25v - 1a + 7.5v - 0.6a + 13v - 0.3a maximum primary current i p ( max ) = 2x p out h x v in ( min ) x t on ( max ) t h : efficiency of the power supply 0.80 < h < 0.85 primary inductance of the transformer l p = v in ( min ) i p ( max ) x t on ( max ) transformer ratio ns np = ( v out + v d ) xt dm v in ( min ) xt on ( max ) reflected voltage v r = 1 t t on ( max ) - 1 xv in ( min ) overvoltage due to the leakage inductance v peak = i p ( max ) 2 x ` ` l f c with : lf = leakage inductance of the transformer 0.04 x lp < lf < 0.10 x lp c = capacitor of the snubber network (see iii.2.2.2) 376-28a.eps / 376-28b.eps figure 28 high performance driver circuits for s.m.p.s 21/33
numerical application to determinate the specifications of the trans- former, it is necessary to make a compromise between a maximum primary current and a maxi- mum voltage on the transistor : - to minimize the maximum primary current with 0.4 < t on ( max ) t < 0.5 - to minimize the maximum voltage on the transis- tor during the demagnetization phase. 0.3 < t on ( max ) t < 0.4 when the output power of the power supply is greater than 100w it is better to minimize the maximum primary current because the current gain b f =i c /i b of bipolar transistor is 1.5 < b f <6 choice : t on ( max ) t < 0.45 i p ( max ) = 2xp out h x v in ( min ) x t on ( max ) t = 2 x 120 0.85 x 210 x 0.45 = 3a l p = v in ( min ) i p ( max ) xt on ( max ) = 210 3 x 0.45 x 64 10 - 6 = 1.95mh v r = 1 t t on ( max ) - 1 xv in ( min ) = 1 1 0.45 - 1 x 210 = 172v v peak will be calculated with the snubber network determination (see ii.2.2.2.1) iii.2.1.1 - transformer specification - reference : orega - smt5 - g4467-03 - mechanical data : - ferrite : b50 - 2 cores : 53 x 18 x 18 (mm) thomson-lcc - airgap : 1.7 mm - electrical data : wind ing pin inductance n p 3-6 1.95 m h n aux 7-9 8.1 m h n2 19-13 770 m h n3 19-20 8.2 m h n4 14-17 4.2 m h n5 22-21 31.7 m h 13 20 19 14 3 6 9 7 17 22 21 376-29.eps figure 29 iii.2.2 - switching transistor and its base drive iii.2.2.1 - first current limitation 376-30a.eps / 376-30b.eps / 376-30c.eps figure 30 : current limitation note : in current limitation tibon < t on high performance driver circuits for s.m.p.s 22/33
the current measurement is i e =i b +i c the maximum collector current calculated in iii.2.1 is i c(max.) = 3a (a switching transistor sgsf344 may be chosen) the current gain is: b f = i c i b + = 3.5 the current limitation is : i e ( max ) = i p ( max ) - ( t s x v in ( min ) l p ) + i b + with : t s = storage time of the switching transistor (typ 3 m s) and vim1 = first threshold of current measurement (typ 0.6 v) r shunt = v im1 i e ( max ) numerical application i e ( max ) = i p ( max ) - ( t s x v in ( min ) l p ) + i b + i e ( max ) = 3 - ( 310 - 6 x 210 1.95 10 - 3 ) + 0.85 = 3.55a r shunt = v im1 i e ( max ) = 0.6 3.255 = 0.169 w iii.2.2.2 - snubber network a r.d.c network is used to limit the overvoltage on the transistor during the switching off time. when the transistor is switched off, the capacitor is charged directly through the diode. when the transistor is switched on, the capacitor is discharged through a resistor. -c = i p ( max ) xt f 2 x vce o 3 - 3xrxc=t on(min) (to discharge the capacitor c by the correct amount) - maximum power dissipated in r : p = 1 2 xcx ( v in ( max ) + v r ) 2 xf 376-31a.eps / 376-31b.eps figure 31 numerical application (with sgsf 344 transis- tor) with : i p(max.) =3a- v in(max.) = 370 vdc t f = 0.3 m s-v r = 172v v ceo = 600v - f = 16khz t on(min.) =4 m s c = i p ( max ) xt f 2x vce o 3 = 3 x 0.3 10 - 6 2x 600 3 = 2.25nf r = t on ( min ) 3xc = 4 10 - 6 3 x 2.25 10 - 9 = 560 w p = 1 2 xcxv in ( max ) + v r ) 2 xf p = 1 2 x 2.25 ? 10 9 x ( 370 + 172 ) 2 x 16 ? 10 3 = 5.29w in the final application a value of 2.7nf is chosen to decrease the overvoltage on the transistor in short circuit condition. high performance driver circuits for s.m.p.s 23/33
iii.2.2.2.1 - overvoltage due to the leakage in- ductance (see. iii.2.1) the capacitor c of the snubber network influences the overvoltage due to the leakage inductance. v peak = i c ( max ) 2 ` l f c numerical application with : l f = 0.08 x l p = 0.08 x 1.9 10 -3 = 152 m h v peak 3 2 x ` 152 10 6 2.25 10 9 = 390v so v ce(max.) =v in(max.) +v r +v peak =v ce(max.) = 370 + 172 + 390 @ 930v iii.2.2.3 - base drive the output stage of the tea2260/61 works in saturation mode and hence the internal power dissipation is very low. r1 = v cc +- v p - v z - v be i b + 376-32a.eps / 376-32b.eps figure 32 numerical application r1 = 13 - 0.9 - 3 - 0.6 0.85 @ 10 w in this case the current gain, bf = i c i b = 3 0.85 = 3.5 but it is recom- manded to verify the vce sat dynamic behaviour on the transistor as follows : see figure 33 376-33a.eps / 376-33b.eps figure 33 ideal value : 1v v cesat +v d 2v remark : the mains of the tea2260/61 must be provided through an isolation transformer for this measurement high performance driver circuits for s.m.p.s 24/33
iii.2.3 - oscillator frequency the free running frequency is given on ii.2. the typical value of minimum conduction time t on(min) on the output of the tea2260/61 is given by: t on(min) = 1040 x c o note : the minimum conduction time ton(min) on the transistor is longer due to the storage time. 376-34.eps figure 34 numerical application f o = 16khz c o is chosen at 1nf so t on min on the tea2260/61 = 1 m s r o = 1 f o xc o x 0.66 - 1.57 10 3 r o = 1 16 10 3 x1 10 - 9 x 0.66 - 1.57 10 3 r o =93k w r o = 100k w is chosen. note : fo is chosen relatively low to avoid magneti- zation of the transformer during the start-up phase. iii.2.4 - regulation loop in stand by mode the error amplifier of the tea2260/61 carries out the regulation. - the r.c. filter is necessary to avoid the peak voltage due to the leakage inductance. the time constant t = rc is about 30 m s < r.c. < 150 m sas a function of the transformer technology. - to achieve a stable behaviour of the regulation loop and to decrease the ripple on the output voltage in stand by mode the time constant should be approximately : ( r1 + r2 + r3 ) xc @ r out xc out 15 376-35.eps figure 35 with : c out (filtering output capacitor) and r out (load resistor on the output in stand by mode) - to ensure a stable behaviour in stand-by mode the amplifier gain is choosen to : g = r4 r2 + r3 @ 15 calculation of r, r1, r2, r3, r4 a) the resistor r is given by r = t c c choosen between 1 m f numerical application s o r = t c = 80 10 - 6 2.2 10 - 6 = 36 w b) the resistors r1, r2, r3 are given by r1 + r2 + r3 @ c out xr out 15 x c with : v ref : reference voltage of the error amplifier v ref = 2.5v v cc (stand by) : vcc voltage in stand by mode. v cc (stand by) = 0.9 x v cc (in normal mode) numerical application with : v cc = 13v v ref = 2.5v r out =2k w on output 135 v c out = 100 m f on output 135 v c = 2.2 m f r1 + r2 + r3 @ c out xr out 15 xc = 100 10 - 6 x2 10 3 15 x 2.2 10 - 6 = 6k w r2 + r3 =( r1 + r2 + r3 ) x v ref v cc ( stand by ) r2 + r3 = 610 3 x 2.5 0.9 x 13 = 1.28k w values choosen : r2 potentiometer resistor of 1k w r3 fixed resistor 1k w r1 = (r1+ r2 + r3) - (r2+ r3) r1 = 6k - 1.28k = 4.7k w c) the resistor r4 is given by r4 @ 15 x (r2 + r3) numerical application r4 @ 15 x (r2 + r3) @ 15 x (1.28 10 3 ) @ 18k w iii.2.5 - overload capacitor when an overload is detected with the first thresh- old vim1 the capacitor c2 (pin 8) is charged until the end of the period as shown in figure 33. so the average load current is given by : ic2 = t - t on t xi ch - i dish the threshold to cut off the tea2260/61 power supply is 2.5v typically and hence the delay time before overload detection is given by : toverload = 2.5 x c2 ( t - t on t xi ch )- i disch 376-36.eps figure 36 : load of overload capacitor numerical application with : maximum overload time = 40 ms the longer delay time is obtained when to n = to n (max) c2 = (( t - ton ( max ) t xi ch )- i disch ) x tov er l o ad 2.5 c2 = (0.55 x 45 10 -6 -10 10 -6 40 10 - 3 2.5 @ 220 nf note : in practice, the overload capacitor value must be greater than the soft start capacitor (c2 c1) to ensure a correct start up phase of the power supply. iii.2.6 - soft start capacitor refer to paragraph ii.5 for the soft start function explanation. the soft start duration is given by : t softstart = ( 2.7 - 1.5 ) xc1 910 - 6 c1 = 7.5 10 - 6 x t soft start numerical application with : tsoft start = 30 ms c1 = 7.5 10 -6 x3010 -3 = 220 nf iii.2.7 - feed back voltage transformer a feedback voltage transformer is used to send information from the secondary circuit (master cir- cuit) to the primary circuit (slave circuit). this transformer is needed to provide an electric insulation between primary and secondary side. the feedback input of tea2260/61 is fed with logic level (threshold 0.9v) it is necessary to have the same waveform on the primary side as on the secondary side. high performance driver circuits for s.m.p.s 26/33
376-37.eps figure 37 for this reason the time constant must be higher than the maximum conduction time in normal mode. hence the primary inductance lp must be calcu- lated as follows : lp > 3.r.t on(max) numerical application with : t on(max) =28 m s r=270 w l p > 3 x 270 x 28 10 -6 = 22mh a) when the tea5170 is used v in =7v ns np = v s ( min ) v in x ( 1 - t on ( max ) t ) ns np = 1.5 7x ( 1 - 0.45 ) = 0.389 b) when the tea 2028 is used v in = 12v ns np = 1.5 12 x ( 1 - 0.45 ) = 0.227 note : the r1.c1 filter is used to damp oscillation on the secondary side of the feedback transformer. the time constant r1 x c1 @ 0.1 m s. iii.2.8 - start up resistor after switching on the power supply the filtering capacitor on v cc of tea2260/61 is charged through a resistor connected to the mains input voltage. do not connect this resistor to the high voltage filtering capacitor because there is enough energy in this capacitor to cause three attempted restarts and to cut off the tea2260/61 on fault detection when the power supply is switched off. hence it is recommended to connect the start-up resistor as follows : 376-38.eps figure 38 start up delay time i moy = ` 2xv in ac ( min ) xr st start-up delay time = tst = v cc start i moy - i cc start xc r st = ` 2 xv in ac ( min ) x ( cx v cc start t st )+ i cc start power dissipated in start up resistor p = v in ac ( max ) 2 2.r st numerical application with : start up delay time = 1s v in(max ) = 370v dc (v in ac(max) = 265v) v in ac(min) = 175v v ccstart = 10.3v i ccstart = 0.7ma c = 220 m f r st = 2 x 175 x ( 220 10 - 6 x 10.3 + 0.7 10 - 3 ) = 26k w value choosen = 22k w power dissipated p = ( 265 ) 2 2x22 10 3 = 1.6w high performance driver circuits for s.m.p.s 27/33
iii.2.9 - determination of high voltage filtering capacitor 376-39a.eps / 376-39b.eps figure 39 hypothesis : d v : ripple on the filtering voltage v in.ac(min) : minimal value of a.c. input voltage t : period of the mains voltage p out : output power of the power supply h : efficiency of the power supply c = t 2 p x p 2 + arcsin ( 1 - d v v in ac ( min ) x `` 2 ) d v in ac ( min ) x ` ` 2 x p out h numerical application d v = 40v v in ac(min) = 170 vac t = 20ms p out = 120w h = 0.85 c = 20 10 - 3 2 p x p 2 + arcsin ( 1 - 40 250 ) 40 x 250 x 120 0.85 =115 m f value choosen : c = 120 m s high performance driver circuits for s.m.p.s 28/33
iii.3 - electrical diagram power primary ground secondary ground (isolated from mains) small signal secondary ground 170 vac 270 vac 4 x 1n4007 120 m f 385v by218-600 plr811 by218-100 by218-100 470 m f 25v 1000 m f 25v 1000 m f 25v 220 m f 25v ba157 1n4148 100pf 2.7nf 1kv by299 47 m f bzx85-3v0 2.2 m h 220 nf 220 nf 1nf 1nf 2.2 m f 16v sgsf 344 3 13 6 20 19 14 7 17 9 22 21 12v 135v 7.5v stand-by control 47nf 1.2 nf 2% 1n4148 150pf sync. input 10 m f 16v 1 8 7 3 24 65 764 5 12 13 16 15 11 10 2 9 8 3 14 1 bc547c 3.3nf tea2260/61 w 120k w 2.2k w 10k w 75 k w w 105k 1% 6.8k w w w 1k 560k 8w w w 0.170 /1w w w w 22k 100k 100 w w w w 36 22k 2w 10 1w w 1k w 1k w w 18k 4.7k p 2 out 2.2 /0.5w 47k w p 1 p : 120w f : 16khz 25v 270 tea5170 100 m f 250v 18 330 w 1 nf 376-40.eps figure 40 high performance driver circuits for s.m.p.s 29/33
iv - tv application 140w - 220 vac - 32khz synchronizable all details concerning the determination of external components are described in section iii. iv.1 - application characteristics - discontinuous mode flyback smps - stand-by function using the burst mode of tea 2260. - switching frequency in burst mode : 16khz - switching frequency in normal mode : 32khz - nominal mains voltage : 220 vac - mains voltage range : 170 vac to 270 vac - output power range in normal mode 25w < po 140w - output power range in stand-by mode 2w < po 45w - efficiency at full load > 80% - efficiency in stand-by mode (po = 7w) > 50% - short circuit protection - long duration overload protection - complete shut down after 3 restarts with fault detection for tea2260 - complete shut down when v c2 reaches 2.6v for tea2261 load regulation (vdc = 310v) output 135v (+/- 0.18%) (i 135 : 0.01a to 0.8a; i 25 = 1a) output 25v (+/- 2%) (i 135 : o.8a; i 25 = 0.5a to 1a) line regulation (i1 35 : 0.8a; i 25 : 1a) output 135v (+/- 0.13%) (210v < v dc < 370v) output 25v (+/- 0.17%) iv.2 - transformer specification - reference : orega.smt5. g4576-03 - electrical data : wind ing pin inductance n p 3-6 790 m h n aux 7-9 5.4 m h n2 19-13 338 m h n3 19-20 4.8 m h n4 14-17 3.4 m h n5 22-21 13 m h 13 20 19 14 3 6 9 7 17 22 21 376-41.eps figure 41 high performance driver circuits for s.m.p.s 30/33
iv.3 - electrical diagram power primary ground secondary ground (isolated from mains) small signal secondary ground 170 vac 270 vac 4 x 1n4007 by218-600 plr811 by218-100 by218-100 470 m f 25v 1000 m f 25v 1000 m f 25v ba157 1n4148 100pf 2.7nf 1kv by299 47 m f bzx85-3v0 2.2 m h 1nf 1nf 2.2 m f 16v sgsf 344 3 13 6 20 19 14 7 17 9 22 21 stand-by control 47nf 1n4148 150pf sync. input 10 m f 16v 1 8 7 3 2 465 76 4 5 12 13 16 15 11 10 2 9 8 3 14 1 bc547c tea2260/61 tea5170 w 120k w 2.2k w 10k w 75 k w w 6.8k w w w 1k w w w w w 18 22k 100 w w w w 10 1w w 1k w 1k w w 4.7k p 2 out 2.2 /0.5w 47k w p 1 135v 0.8a 7.5v 1a 12v 0.5a 25v 1a 1.2nf 560 pf 2% 100k 1% 220 16w 0.135 /1w 330 nf 330 nf 22k 3.3 nf 150 m f 385v 22k 3w 39 330 m f 25v p : 140w f : 32khz 82k 270 100 m f 250v 330 w 1 nf 376-42.eps figure 42 high performance driver circuits for s.m.p.s 31/33
v - tv application 110w -220 vac - 40khz regulated with optocoupler this application works in asynchronous mode. the regulation characteristics are very attractive (out- put power variation range from 1w to 110w due to automatic burst mode (see ii.6). in this configura- tion higher is the regulation loop gain, lower is the output voltage ripple in burst mode (e.g. ouput voltage ripple 0.8% with a loop gain of 15). v.1 - frequency soft start the nominal switching frequency is 40khz but dur- ing the start-up phase the switching frequency is shifted to 10khz in order to avoid the magnetization of the transformer. otherwise the second current limitation will be reached at high input voltage and hence the power supply will not start. v.2 - application characteristics - discontinous mode flyback smps - switching frequency : 40khz - nominal mains voltage : 220 vac - mains voltage range : 170 vac to 220 vac - output power in normal mode : 30w < po < 110w - output power in burst mode : 1w < po < 30w.the transient phase between normal mode and burst mode is determinated automatically as a function of the output power. hence the regulation of the output voltage is effective for an output power variation of 1w < po < 110w - efficiency as full load > 80% - efficiency in burst mode (po = 8w) > 50% - short circuit protection - open load protection - long duration overload protection - complete shutdown after 3 restarts with fault detection for tea2260 - complete shut down when v c2 reaches 2.6v for tea2261 load regulation (vdc = 310v) output 135v (+/- 0.15%) (i 135 : 0.05a to 0.6a; i 25 = 1a) output 25v (+/- 2.5%) (i 135 = 0.6a; i 25 : 0.25 to 1a) line regulation (i 135 : 0.6a; i 25 : 1a) output 135v (+/- 0.30%) (210v < vdc <, 370v) output 25v (+/- 0.30%) influence of the audio output on the video out- put output 135v (+/- 0.1%) (i 135 = 0.6a; i 25 :0 1a) output 135v (+/- 0.05%) (i 135 = 0.3a; i 25 :0 1a v.3 - transformer specification - reference : orega.smt5. g4576-02 - mechanical data : - ferrite : b50 - 2 cores : 53 x 18 x 18(mm) thomson lcc - electrical data : wind ing pin inductance n p 3-6 790 m h n aux 7-9 5.4 m h n2 19-13 338 m h n3 19-20 4.8 m h n4 14-17 3.4 m h n5 22-21 13 m h 13 20 19 14 3 6 9 7 17 22 21 376-43.eps figure 43 high performance driver circuits for s.m.p.s 32/33
v.4 - electrical diagram power primary ground secondary ground (isolated from mains) small signal secondaryground 170 vac 270 vac 4 x 1n4007 by218-600 plr811 by218-100 by218-100 470 m f 25v ba157 2.7nf 1kv by299 47 m f bzx85-3v0 2.2 m h sgsf 344 313 6 20 19 14 717 9 22 21 7645 12 13 16 15 11 10 298 3 14 1 tea2260/61 w 120k w w w w w w w 18 100 w w w w w w out 2.2 /0.5w 25v 1a 220 16w 330 m f 25v 135v 0.7a 12v 0.5a 39 nf 560 2.2k 10 2w 45 2.2k 120 m f 385v 22k 2w 1 m f1 m f 680 pf w 220k w 56k 2.2m bc547 27 nf 0.120 /1w 4.7k w 4.7k 7.5v 1a bc547a 1 2 cnx62 2.2 k bzx55c6v2 10nf 470 m f 25v 470 m f 40v p : 110w f : 40khz 100 m f 250v 1 nf 330 w 376-44.eps figure 44 high performance driver circuits for s.m.p.s 33/33
information furnished is believed to be accurate and reliable. however, sgs-thomson microelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no licence is granted by implication or otherwise under any patent or patent rights of sgs-thomson microelectronics. specifications mentioned in this publication are subject to change without noti ce. this publication supersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of sgs-thomson microelectronics. ? 1994 sgs-thomson microelectronics - all rights reserved purchase of i 2 c components of sgs-thomson microelectronics, conveys a license under the philips i 2 c patent. rights to use these components in a i 2 c system, is granted provided that the system confo rms to the i 2 c standard specifications as defined by philips. sgs-thomson microelectronics group of companies australia - brazil - china - france - germany - hong kong - italy - japan - korea - malaysia - malta - morocco the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a.

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