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september 2012 doc id 15394 rev 1 1/27 AN2934 application note steval-isa062v1: 6 w, wide-range dual and single output smps demonstration board based on the viper17 by john lo giudice introduction the new viper17 device is a converter that offers a pwm controller built in bcd6 technology and an 800 v, avalanche-rugged vertical power section all in one package. the converter is housed in a dip7 or surface-mount so-16 narrow package. the device has two fixed switching frequencies: the viper17ln switches at 60 khz and the viper17hn at 115 khz. the device can deliver 6 w from wide-range operation from 85 to 305 vac. it can also deliver 10 w when operating from the european range of 175 to 264 vac. the viper17 incorporates the following additional features in high demand from customers. burst mode operation has been improved from earlier vipers, providing a switching power supply standby wattage as low as 50 mw at no load frequency jittering is implemented to ensure emi measurements meet today's standards. adjustable overload output short-circuit protection for hard shorts such as transformer saturation or shorted diode adjustable brownout and power surge features output overvoltage protection. not all of these additional features are necessary to operate the converter and some may be omitted to reduce part count. figure 1. viper17 dual output demonstration board am0 3 41 8 v1 www.st.com
contents AN2934 2/27 doc id 15394 rev 1 contents 1 circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4 pins and their functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1 brownout and power surge features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2 cont pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.3 v dd pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.4 feedback pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5 experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.1 regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.2 transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.3 standby and efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6 comparison of emi for single and dual output device with and without shield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 6.1 main switch waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 6.2 frequency jittering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 6.3 soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7 pcb layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8 conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 9 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
AN2934 list of tables doc id 15394 rev 1 3/27 list of tables table 1. dual output board specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 table 2. single output board specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 table 3. bill of materials for dual output, 5 v at 0.5 a and 12 v at 0.25 a . . . . . . . . . . . . . . . . . . . . . 8 table 4. bill of materials for single output, 12 v at 0.5 a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 table 5. bill of material changes for single output of 12 v at 0.5 a from dual output . . . . . . . . . . . . 10 table 6. bill of material changes for single output of 5 v at 1 a from dual output . . . . . . . . . . . . . . 11 table 7. regulation for dual output: with shield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 table 8. regulation for dual output: without shield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 table 9. regulation for single output: with shield and single primary . . . . . . . . . . . . . . . . . . . . . . . . 16 table 10. regulation for single output: without shield and single primary . . . . . . . . . . . . . . . . . . . . . 16 table 11. transformer parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 table 12. document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
list of figures AN2934 4/27 doc id 15394 rev 1 list of figures figure 1. viper17 dual output demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 figure 2. schematic for dual output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 3. schematic for single output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 figure 4. 165 ms ride-through . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 figure 5. 128 ms ride-through . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 figure 6. overload setpoint at 115 vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 figure 7. transformers for dual output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 figure 8. transformers for single output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 figure 9. transformer specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 figure 10. standby power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 figure 11. efficiency vs vin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 figure 12. efficiency vs load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 figure 13. dual output with shielded transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 figure 14. dual output without shielded transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 figure 15. comparison of emi for single output with and without shield . . . . . . . . . . . . . . . . . . . . . . . 21 figure 16. 85 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 figure 17. 264 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 figure 18. frequency jittering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 figure 19. soft-start feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 figure 20. board: top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 figure 21. board: bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
AN2934 circuit description doc id 15394 rev 1 5/27 1 circuit description the viper17 has two switching frequencies: the viper17hn switches at 115 khz and the viper17ln at 60 khz. the choice of frequency is left up to the designer. the "hn" version makes the transformer smaller, whereas the "ln" version makes it easier to optimize emi. this document focuses on the viper17hn, switching at 115 hz. the following description refers to the circuit shown in figure 1 . the board has been designed so that it can be used with either single or double outputs, the only difference being the extra output parts, the transformer and the voltage divider for the feedback loop. for the board?s operation, we have taken as example the dual output. the input is connected to the line input, which operates from 85 to 264 vac. it is fused for safety and has 6.8 ohms ? w. a carbon resistor is better for inrush than carbon or metal film. if a surge is required, a 2 to 3 w wire-wound resistor should be used to pass the 6 kv ring wave test. c1 is a 0.1 f x capacitor and l1 forms an emi filter to reduce line-conducted emissions. br1 is a bridge rectifier and the c3 filter is the input line to a dc level. the topology used is of a discontinuous flyback type with an isolated output. the regulation comes from the output (as opposed to a stable tl431, which uses an optocoupler for isolation) to feed the information back to the viper17hn. table 1. dual output board specifications parameter limits input voltage range 85 vac to 264 vac input frequency 47 hz to 63 hz temperature range 0 to 85 celsius, 105c possible output voltage and current # 1 5 v at 0.5 a output voltage and current # 2 12 v at 0.25 a load and cross regulation #1 +/-1% load and cross regulation #2 +/-10% output power 5.5 w line regulation +/- 0.2% efficiency 80% typical at 12 v output safety overvoltage, overcurrent, brownout emi en55022 class ?b? table 2. single output board specifications parameter limits output voltage and current 12 v at 0.5 a, 6 w load regulation +/- 1%
schematics AN2934 6/27 doc id 15394 rev 1 2 schematics figure 2. schematic for dual output am0 3 419v1 d7 pkc-136 c4 22uf 25v w1 1 2 5v 500ma d2 1n4148 a k csm16vt-070 t1 4 3 1 2 10 8 5 6 470uh l1 j4 phoenix 3 pin 1 2 3 n br r0 6.8 1 2 d6 stth102a a k d1 1n4148 + c13 470uf 25v r1 10 r3 47k l2 1uh c10 100uf 25v c7 33nf c6 3.3nf r4 1600k r5 22k d4 stps1l40u c9 470uf 25v u2 ts2431 2 1 3 r6 1k r8 2.49k 1% r9 2.49k 1% r10 82k -+ br1 bridge 4 1 3 2 c11 33nf c3 22uf 400v j1 con2 1 2 r2 1600k f1 500ma c1 0.1u c12 0.001uf r14 180k r12 8.2k j3 jumper 1 3 2 c8 2.2nf brown out cont drain source control vd d fb u1 viper 1 7 h n 4 2 8 1 3 5 7 r13 220 opto1 h11a817a 1 2 4 3 12v 250ma
AN2934 schematics doc id 15394 rev 1 7/27 figure 3. schematic for single output am0 3 420v1 w1 1 2 d7 pkc-136 csm16vt-066 t1 4 3 10 8 5 6 r0 6.8 1 2 d1 1n4148 c4 22uf 25v r1 10 r3 47k l2 1uh c10 100uf 25v c7 33nf c6 3.3nf r4 1600k r5 22k d4 stps2h100a c9 470uf 25v u2 ts2431 2 1 3 r6 1k r8 15k 1% r9 3.92k 1% r10 82k -+ br1 bridge 4 1 3 2 c11 33nf c3 22uf j1 con2 1 2 470uh l1 r2 1600k f1 500ma c1 0.1u c12 0.001uf d2 1n4148 r14 180k r12 8.2k j3 jumper 1 3 2 c8 2.2nf brown out cont drain source control vd d fb u1 viper 1 7 h n 4 2 8 1 3 5 7 r13 1k opto1 h11a817 1 2 4 3 12v 500ma j2 con2 1 2
bill of materials AN2934 8/27 doc id 15394 rev 1 3 bill of materials table 3. bill of materials for dual output, 5 v at 0.5 a and 12 v at 0.25 a ref. part volt/watt description cat # br1 bridge c1 0.1 p4610 c3 22 f 400 v 105c compostar ltech tyd2dm220j20o c4 22 f 25 v gp panasonic eet-hc2g561da c6 3.3 nf sm 0805 c7 33 nf sm 0805 c8 2.2 nf y1 panasonic eck-ana222me c9 470 f 25 v low esr panasonic eeu-fc1e471 c10 100 f 25 v gp panasonic eeu-fc1e101s c11 33 nf 50 v sm 0805 c12 0.001 f 50 v sm 0805 c13 470 f 25 v panasonic eeu-fc1e471 d1 1n4148 100 v sod 123 diodes inc 1n4148w-7 d2 1n4148 100 v th 1n4148 d4 stps1l40u stmicroelectronics d6 stth102a stmicroelectronics d7 pkc-136 stmicroelectronics f1 500 ma wickmann usa inc 37204000411 j1 con2 2 position phoenix contact 1729018 j3 jumper 3 pins j4 phoenix 3 pin 3 position phoenix contact 1729021 l1 470 h l2 1 h coil craft me3220-102ml or ice components lo32-1r0-rm opto1 h11a817a h11a817a r0 6.8 1/4 w carbon comp od68gj r1 10 5% 1/4 w r2 1600 k sm 0805 r3 47 k sm 0805 r4 1600 k sm 0805 r5 22 k sm 0805 r6 1 k sm 0805
AN2934 bill of materials doc id 15394 rev 1 9/27 r8 2.49 k 1% sm 0805 r9 2.49 k 1% sm 0805 r10 82 k sm 0805 r12 8.2 k sm 0805 r13 220 sm 0805 r14 180 k sm 0805 t1 csm16vt-070 cramer coil vsm16vt-070 u1 viper17hn stmicroelectronics u2 ts2431 stmicroelectronics w1 val 0805 jumper p3 shorting strap sullins stc02syan table 3. bill of materials for dual output, 5 v at 0.5 a and 12 v at 0.25 a (continued) ref. part volt/watt description cat # table 4. bill of materials for single output, 12 v at 0.5 a ref part volt/watt description cat # br1 bridge c1 0.1 p4610 c3 22 f 400 v 105c compostar ltech tyd2dm220j20o c4 22 f 25 v gp panasonic eet-hc2g561da c6 3.3 nf sm 0805 c7 33 nf sm0805 c8 2.2 nf y1 panasonic eck-ana222me c9 470 f 25 v low esr panasonic eeu-fc1e471 c10 100 f 25 v gp panasonic eeu-fc1e101s c11 33 nf 50 v sm 0805 c12 0.001 f 50 v sm 0805 d1 1n4148 100 v sod123 diodes inc 1n4148w-7 d2 1n4148 100 v th fairchild 1n4148 d4 stps2h100apkc- 136 stmicroelectronics d7 500 ma stmicroelectronics f1 con2 wickmann usa inc 372040004411 j1 con2 2 position phoenix contact 1729018 j2 jumper 2 position phoenix contact 1729018 j3 470 h l1 470 h
bill of materials AN2934 10/27 doc id 15394 rev 1 the same pc board is used for both dual and single output by deleting the second output components and changing the transformer as described in ta bl e 5 . l2 1 h coil craft me3220-102ml or ice components lo32-1r0-rm opto1 h11a817 h11817a r0 6.8 1/4 w carbon comp od68gj r1 10 5% 1/4 w r2 1600 k sm 0805 r3 47 k sm 0805 r4 1600 k sm 0805 r5 22 k sm 0805 r6 1 k sm 0805 r8 15 k 1% sm 0805 r9 3.92 k 1% sm 0805 r10 82 k sm 0805 r12 8.2 k sm 0805 r13 1 k sm 0805 r14 180 k sm 0805 t1 csm16vt-081 cramer coil csm16vt-081 u1 viper17hn stmicroelectronics u2 ts2431 stmicroelectronics w1 val 0805 jumper p3 shorting strap sullins stc02syan table 4. bill of materials for single output, 12 v at 0.5 a (continued) ref part volt/watt description cat # table 5. bill of material changes for single output of 12 v at 0.5 a from dual output (1) item ref. part volt/watt description cat # omit c13 470 f 25 v panasonic eeu-fc1e471 omit d6 stth102a stmicroelectronics omit t1 csm16vt-081 cramer coil csm16vt-081 change d4 stps2h100a stmicroelectronics change j4 phoenix 2 pin 2 position phoenix contact 1729018 change r13 1 k sm 0805 change r8 15 k 1% sm 0805 change r9 3.92 k 1% sm 0805 1. parts changed to make a single output power supply of 12 v at 0.5 a.
AN2934 bill of materials doc id 15394 rev 1 11/27 the viper17hn has several extra features that can be implemented if needed. table 6. bill of material changes for single output of 5 v at 1 a from dual output (1) item ref. part volt/watt description cat # omit c13 470 f 25 v panasonic eeu-fc1e471 omit d6 stth102a stmicroelectronics change t1 csm16vt-084 cramer coil csm16vt-084 change d4 stps3l60u stmicroelectronics change c9 820 f 25 v panasonic eeu-fc1e821 change j4 phoenix 2 pin 2 position phoenix contact 1729018 change r13 390 sm 0805 change r8 3.92 k 1% sm 0805 change r9 3.92 k 1% sm 0805 1. parts changed to make a single output power supply of 5 v at 1 a.
pins and their functions AN2934 12/27 doc id 15394 rev 1 4 pins and their functions 4.1 brownout and power surge features the viper17hn has a dedicated pin?called the br pin? for the brownout and power surge features. this pin (pin 5) has its comparator set for a 0.45 v input. the unit?s shutdown and start-up can be set to the desired line voltages by attaching a resistor divider from the bulk to this pin. if this feature is not required, the pin can be grounded. the j3 jumper is used for this purpose. when the jumper is installed on the left-two pins marked "n", the brownout is grounded or defeated. with the unit set to half the output power, it shuts down at 32 vac and restarts at 53 vac. when the jumper is installed on the right-two pins marked "br", the brownout feature is active and the unit shuts down at 60 vac and restarts at 70 vac. in today's appliances, such as washing machines, dryers, dishwashers and the like, mechanical timers have been replaced with electronics. when the ac line drops for a short duration, the appliance must ride through its cycle without going back to the beginning. if the ac line drops for a longer period, information about where the appliance is in the cycle must be saved. when the ac line comes back, the appliance has to continue from where it left off and not start over again. this is known as the "hold-up time". ride-through is defined as the input line voltage dropping for a number of cycles and the unit under test continuing to operate correctly without the microprocessor being reset. typically, tests are done at a nominal 115 vac. the line is sensed and when missing pulses are detected, the unit starts shedding loads, saves the settings and tries to "ride through" the line dropout. if the input line does not come back in time, the power supply has to maintain an output voltage until all the information has been saved. when the line does come back, the cycle starts again from where it left off instead of from the beginning. since e=? c(v 2 start-v 2 end), most of the energy comes from the v 2 of the input capacitor (c3). the delta from the starting input voltage to the point where the pwm stops is the time the unit runs for. the brownout pin turns off the unit at a certain voltage, reducing stress on the components but affecting the hold-up time. c12 may be increased to delay the turn-off, forming an rc time constant and therefore achieving a good hold-up, but turning off the unit if the voltage dwells at a low line. the customer must evaluate the stresses on the components with regard to the hold-up required. the plots in figure 4 and figure 5 show the difference between the two settings of j3 on the single reference board. the strap can be set to ground (n) or to (br) with brownout active. with the strap in the (n) position, the input capacitor can discharge to ~45 vdc before a glitch becomes noticeable on the main output. with the strap in the (br) position, the brownout is active and stops the pwm from switching when the voltage on the input capacitor reaches a predetermined voltage set by the brownout divider. vout is equal to 0.45 vdc. equation 1 vin vout r1 r2 + () r2 ---------------------------------------- - =
AN2934 pins and their functions doc id 15394 rev 1 13/27 both figures show a ride-through from 115 vac at a12 v/100 ma constant current load. figure 4 shows that the bulk voltage (yellow trace) can reach 45 vdc before a glitch becomes visible on the output (green trace). with the brownout pin active, we can see a definite pulse shutdown at ~70 vdc. the purple trace is the ac line. note that one contradicts the other: the higher the difference of input voltage, the longer the hold-up or ride-through. 4.2 cont pin the cont pin has multiple purposes. one of them is to reduce the output current or power. a resistor can be set from this pin to ground to reduce the pulse-by-pulse current limit according to figure 16 "current limit vs. rlim" in the viper17 datasheet (a) . this is useful when lower power is needed and a smaller transformer is used as it prevents saturation of the transformer. the results of this function can be seen in figure 6 . the function itself can be activated by changing r3 on the viper17hn reference board. a second-level protection, which latches the device if exceeded, ensures safety in the case of transformer or diode shorts. if the viper17 detects a current pulse of 600 ma, it considers it to be a disturbance; if it detects this disturbance two consecutive times, it interprets it as a hard short and shuts down. another purpose of the cont pin is overvoltage monitoring. a voltage over 3 v shuts down the ic, reducing power consumption, which is useful for overvoltage sensing or if there is an open component in the feedback loop caused by faulty soldering. this monitoring function has been tested by paralleling a resistor with r9 to raise the output voltage. the unit went into a "hiccup" mode at an output voltage of 18 v. the voltage limit can be adjusted as needed by changing r14. figure 4. 165 ms ride-through figure 5. 128 ms ride-through am0 3 421v1 am0 3 422v1 a. refer to the datasheet viper17: off-line high voltage converters available on www.st.com.
pins and their functions AN2934 14/27 doc id 15394 rev 1 figure 6. overload setpoint at 115 vac 4.3 v dd pin the v dd pin is connected to an electrolytic capacitor that is charged during start-up by an internal constant-current source inside the viper17hn. this pin is only enabled if the input voltage is higher than 80 vdc at the drain of the device. it is fixed and not dependent on the brownout section. once v dd reaches the start threshold of 15 v maximum, the viper17hn shuts off the current source and starts switching. the charge current at start-up is 3 ma. if a fault is detected, the charge current is reduced to 0.6 ma to obtain a slow duty cycle during the restart phase and prevent overheating. the mosfet is an 800 v minimum, avalanche- rugged n channel with a typical r ds(on) of 20 at 25c. the viper17hn also has a soft- start feature that progressively raises the drain current limitation to the maximum value as shown in figure 19 . in this way, stresses on other components are considerably reduced. 4.4 feedback pin the feedback pin is the control input for duty cycle control. a voltage below 0.5 v activates the burst mode operation. the upper level of 3.3 v borders on the cycle-by-cycle overcurrent setpoint. for isolation this pin can be controlled by an optocoupler. the feedback point is tied to 12 v in the single output reference design and to 5 v in the dual reference design. it is normally tied before l2 to avoid a phase shift. am0 3 42 3 v1 oc trip v s rlim 0 0.1 0.2 0. 3 0.4 0.5 0.6 0.7 0. 8 0.9 1 0 1020304050607080 r 3 or rlim c u rrent
AN2934 experimental results doc id 15394 rev 1 15/27 5 experimental results this section focuses on a power supply tested at 25 celsius. the results are given as typical of the unit and may vary from unit to unit. 5.1 regulation regulation has been tested from 10% to 100%. efficiency and ripple have been tested at full load. two transformers were experimented: one with a single primary and a wired shield and the other with a split primary and no shield. the shield minimizes line-conducted noise more than the solution without the shield by some additional 5 db, but the drawback of the shielded transformer is dissipation and less efficiency. table 7. regulation for dual output: with shield vin 5 v load 12 v load 5 v 12 v w in efficiency vdd 85 vac 0.05 0.025 5.02 12.33 0.81 12.22 85 vac 0.05 0.25 5.01 11.58 4.09 11.96 85 vac 0.5 0.025 4.97 13.83 3.76 13.56 85 vac 0.5 0.25 4.99 12.4 7.07 79.1% 12.75 264 vac 0.5 0.25 4.99 12.4 7.42 75.4% 12.74 minimum 4.97 11.58 11.96 maximum 5.02 13.83 13.56 delta 0.05 2.25 1.6 line regulation 0.0% 0.0% 0.1% +/-% load/cross regulation 0.5% 9.1% 6.3% ripple mv pp 10 61 input wattage at no load at 115 vac in mw 61 short-circuit ok ok table 8. regulation for dual output: without shield (1) vin 5 v load 12 v load 5 v 12 v w in efficiency vdd 85 vac 0.05 0.025 5.02 12.47 0.72 13.08 85 vac 0.05 0.25 5.02 11.93 3.81 16.12 85 vac 0.5 0.025 5 14.26 3.53 16.72 85 vac 0.5 0.25 4.99 12.56 6.95 81.1% 17.29 264 vac 0.5 0.25 4.99 12.55 6.94 81.2% 16.75 minimum 4.99 11.93 13.08 maximum 5.02 14.26 17.29
experimental results AN2934 16/27 doc id 15394 rev 1 for the dual output board, the second output relies on the main output for regulation. 10% regulation is typical for load and cross regulation for a swing of 10% to 100% of the output?s maximum load. the ripple on the first output is very low because of the pie filter (l2, c10) that eliminates the switching ripple and the spikes. delta 0.03 2.33 4.21 line regulation 0.0% 0.1% 3.3% +/-% load/cross regulation 0.3% 9.3% 12.2% ripple mv pp 25 75 input wattage at no load at 115 vac in mw 42 short-circuit ok ok 1. unit #1, csm16vt-082 split primary, no shield. table 8. regulation for dual output: without shield (1) (continued) vin 5 v load 12 v load 5 v 12 v w in efficiency vdd table 9. regulation for single output: with shield and single primary (1) vin a at 12 v 12 vout w in i in efficiency vdd 85 vac 0.05 12.01 0.87 11.93 85 vac 0.5 11.98 7.38 81.2% 12.27 264 vac 0.05 12.01 1.24 11.99 264 vac 0.5 11.98 7.91 75.7% 12.26 minimum 11.98 11.99 maximum 12.01 12.27 delta 0.03 0.28 line regulation 0.00% 0.08% +/-% load/cross regulation 0.12% 1.17% ripple in mv pp at 115 22 input at no load at 115 vac in mw 82 short-circuit ok 1. viper17hn unit #1 green with csm16vt-066e with shield. table 10. regulation for single output: without shield and single primary (1) vin a at 12 v 12 vout w in i in efficiency vdd 85 vac 0.05 12.00 0.787 11.91 85 vac 0.5 11.97 7.37 81.2% 12.27 264 vac 0.05 12.00 0.907 11.93 264 vac 0.5 11.97 7.31 81.9% 12.28 minimum 11.97 11.93 maximum 12.00 12.28 delta 0.03 0.35
AN2934 experimental results doc id 15394 rev 1 17/27 as shown in the above tables for the double and single outputs, line and load regulation are excellent. the shield helps to protect the device from emi, as shown in figure 15 , but at the expense of efficiency due to the extra wattage in the transformer?s energy dissipated as a result of the coupling between the primary and the shield at high lines. 5.2 transformers figure 9. transformer specifications line regulation 0.00% 0.08% +/-% load/cross regulation 0.12% 1.47% ripple in mv pp at 115 25 input at no load at 115 vac in mw 86 short-circuit ok 1. viper17hn unit #1 with single primary, no shield csm16vt-081. table 10. regulation for single output: without shield and single primary (1) (continued) vin a at 12 v 12 vout w in i in efficiency vdd figure 7. transformers for dual output figure 8. transformers for single output am0 3 424v1 0 8 2 070 am0 3 425v1 am0 3 426v1
experimental results AN2934 18/27 doc id 15394 rev 1 note: core material is tdk pc40 or equivalent. high potential is 4000 vac for 1 second. operating frequency is 115 khz. table 11. transformer parameters part # winding pins primary inductance number of turns wire type d u a l o u t p u t (5 v and 12 v), shield, single primary csm 16vt-070 shield nc-10 40 34 awg primary 8-10 1.36 mh +/-10% 95 34 awg 5 v 4-3 5 0.45 mm triple-insulated 12 v 1-2 12 0.25 mm triple-insulated vdd 5-6 12 34 awg dual output (5 v and 12 v), no shield, split primary csm 16vt-082 primary 8-10 1.36 mh +/-10% 95 34 awg 5 v 4-3 5 0.45 mm triple-insulated 12 v 1-2 12 0.25 mm triple-insulated vdd 5-6 12 34 awg 12 v single output, shield, single primary csm 16vt-066 shield nc-10 40 34 awg primary 8-10 1.36 mh +/-10% 95 34 awg 12 v 4-3 12 0.32 mm triple-insulated vdd 5-6 12 34 awg 12 v single output, no shield, single primary csm 16vt-081 primary 8-10 1.36 mh +/-10% 95 34 awg 12 v 4-3 12 2 x 0.32 mm triple-insulated vdd 5-6 12 34 awg 5 v single output, no shield, single primary csm 16vt-084 primary 8-10 1.36 mh +/-10% 95 34 awg 5 v 4-3 5 2 x 0.32 mm triple-insulated vdd 5-6 12 34 awg
AN2934 experimental results doc id 15394 rev 1 19/27 5.3 standby and efficiency figure 10 shows the board?s standby power. if designing the board with low consumption in mind, a higher impedance should be used for r8, r9 and r13. figure 10. standby power the board?s efficiency with respect to the line voltage and load has also been measured and is shown in figure 11 and figure 12 . figure 11. efficiency vs vin am044 3 5v1 standby power 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 80 130 180 230 280 vac input wattage
experimental results AN2934 20/27 doc id 15394 rev 1 figure 12. efficiency vs load
AN2934 comparison of emi for single and dual output device with and without shield doc id 15394 rev 1 21/27 6 comparison of emi for single and dual output device with and without shield figure 15. comparison of emi for single output with and without shield the readings in the above plot are of 3 max and hold (scanned three times, with the graph displaying the highest reading). the green trace is the dual output transformer with a wire shield and efficiency of 75.7%. the blue trace is the dual output without shield but with an efficiency of 81.2%. the choice has been made to go with the regular, non-shielded transformer since it is still 5 db under the peak limit with better efficiency. figure 13. dual output with shielded transformer figure 14. dual output without shielded transformer am0 3 427v1 am0 3 42 8 v1 am0 3 429v1
comparison of emi for single and dual output device with and without shield AN2934 22/27 doc id 15394 rev 1 6.1 main switch waveforms figure 16 shows the mosfet?s drain voltage and current waveforms for a minimum line of 85 v, and figure 17 shows the waveforms at a high line of 264 v. both measurements have been taken at a full load of 12 v at 0.5 a. 6.2 frequency jittering figure 18 shows the drain current and vfb at maximum load. jittering causes the drain current and the feedback voltage to modulate with a triangular wave. if the power supply had been operating at a fixed frequency, the drain current would be proportional to the output power. if you compare three or more current waveforms, you can see that the middle one stays still while the ones to the left and right tend to fluctuate from the middle. this indicates that the switching frequency is being modulated. figure 18. frequency jittering figure 16. 85 v figure 17. 264 v am0 3 4 3 0v1 am0 3 4 3 1v1 am0 3 4 3 2v1
AN2934 comparison of emi for single and dual output device with and without shield doc id 15394 rev 1 23/27 6.3 soft-start when the power supply starts, the output capacitors need to be charged up to the operating voltage. during this initial time, the converter has to charge the output capacitors plus deliver any output current required. this results in the maximum current being delivered to the output. the maximum output current is proportional to the primary current limited by the pulse-by-pulse current limit of the device. with the soft-start feature, the current?s trip level is raised in 16 equal steps for a total duration of 8.5 ms. this prevents the current from reaching a higher value during the start-up time. figure 19 shows the soft-start feature of the converter. figure 19. soft-start feature am0 3 4 33 v1
pcb layout AN2934 24/27 doc id 15394 rev 1 7 pcb layout the board measures 95 x 35 mm and has both through holes and surface-mount components on the bottom. this makes the design compact and good for line-conducted noise by eliminating the common-mode choke with a single inductor. figure 20 shows the placement of the components. the bottom view shows the foil traces and surface-mount components. figure 20. board: top view figure 21. board: bottom view this is a reference design only and can be modified according to specific needs. am0 3 4 3 4v1 am0 3 4 3 5v1
AN2934 conclusion doc id 15394 rev 1 25/27 8 conclusion this application note describes a dual and single output flyback converter demonstration board using the viper17hn device. both output types can be achieved with the same printed circuit board. the device integrates input from customers by offering several protections and a built-in 800 v, avalanche-rugged power section. it also provides efficient short-circuit, overload and overvoltage protections, and consumes little power at no load.
revision history AN2934 26/27 doc id 15394 rev 1 9 revision history table 12. document revision history date revision changes 27-sep-2012 1 initial release.
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