PSU DESIGN FullBridge + StepDown 0-150V 10A - Page 1
Forum section: electronics / projects

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 10, 2021, 11:32:22 am
content: hmm It seems its hard to find IC on stock.I looked on UC3526 its old IC but i dont need something fancy.https://www.ti.com/lit/ds/symlink/uc2526a.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&ts=1639134818280&ref_url=https%253A%252F%252Fcz.mouser.com%252FBut what i dont like about it, there are no application notes for full bridge design.My plan is to make 0-150V PSU, Full bridge will set voltage on 75 / 150V on first output stage for step down converter according to desirable output voltage.Since i want 1,5kW (150V 10A) Fullbridge is probably the way. Two switch forward will be easier but i would need bigger transformer (double current), more caps...In other hand i need more transistors, drivers, maybe heatsinks... on full bridge.What do you think will UC3526 fit? I will draw schematic of primary side and then post it, if everything is correct.Good thing about UC3526 is its on stock even in czech republic...

author: strawberry
author_rank: Super Contributor
timestamp: December 10, 2021, 05:25:53 pm
content: similar to UC3525

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 10, 2021, 07:26:16 pm
content: ThanksI need galvanic isolated mosfet drivers. Can you recommend me something? 1,5A would be more than enough.Or maybe i should use signal isolator and then mosfet driver connected to bootstrap capacitor. I think it will be hard to layout driver as near as possible to mosfet and at the same time check distance clearence of primary / secondary side.

author: strawberry
author_rank: Super Contributor
timestamp: December 10, 2021, 08:24:44 pm
content: http://danyk.cz/reg60v_en.htmlhttps://320volt.com/en/13-8v-40-amper-smps-guc-kaynagi-etd59-tl494/494/7500 can do full bridge

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 10, 2021, 08:56:58 pm
content: i know danyk.cz well, but i am not sure about tl494, if you take look on page 5 there are output emitors ON at the same time. It will result into short circuit. But even in half bridge it cant turn both transistors on at the same time. So i am little bit confused now.https://www.onsemi.com/pdf/datasheet/tl494-d.pdfFrom schematic posted herehttps://f6gky-pagesperso--orange-fr.translate.goog/alimdecoup.htm?_x_tr_sl=auto&_x_tr_tl=tr&_x_tr_hl=trwhen both signals are on magnetic flux in GDT cancel and gdt transformer get shorted i guess.

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 11, 2021, 10:02:58 am
content: Can auxilary winding overheat zener diode inside IC? I never powered primary from auxilary winding, but it will be effective to use it. I am just scared of overheating ic... I use this transformer for 12V at secondaryhttps://cdn.sos.sk/productdata/dd/30/d06ff055/74080.pdfAUX:https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/dot1.png

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 12, 2021, 11:25:52 am
content: Is ok to connect negative RESET input to VREF via 10K resistor?https://www.ti.com/lit/ds/symlink/uc2526.pdf?ts=1639302770780&ref_url=https%253A%252F%252Fwww.google.com%252F

author: strawberry
author_rank: Super Contributor
timestamp: December 12, 2021, 12:11:26 pm
content: zener internal resistance is some ~10ohm, feeding with low impedance constant voltage source will damage zenerUC2526 RESET pin have open colector with internal 5V 20k pull-up resistor ,

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 12, 2021, 12:34:08 pm
content: thanks,what about unused current sense pins of inverted schmitt trigger inside uc3526byppas capacitor to +cs and ground to -cs?*I need logic 1 on output of schmit trigger. -cs is reference voltage, If there is 0,1V on +cs pin and 0V on -cs pin, then there should be logic 0 on output (becouse its inverted) so in need to have -cs on higher potential. Thats kinda weird current control =)

author: strawberry
author_rank: Super Contributor
timestamp: December 12, 2021, 01:05:34 pm
content: +CS > -CS overcurrent activecurrent sense amplifier output is invertedcould use current sense transformer

author: george.b
author_rank: Frequent Contributor
timestamp: December 12, 2021, 04:17:09 pm
content: Quote from: MacIntoshCZ on December 10, 2021, 08:56:58 pmIf you look at the bottom trace in the graph you're concerned about, you'll see that those emitters go high at the same time just as Output Control, the bottom trace, goes low. Output Control selects between single-ended and push-pull modes.

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 12, 2021, 05:47:14 pm
content: Right, i missed it

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 12, 2021, 06:50:22 pm
content: I would like to ask if its good idea to add rc filter before error amplifier which does voltage feedback.

author: strawberry
author_rank: Super Contributor
timestamp: December 12, 2021, 07:54:45 pm
content: remove R19, R24, C23, C24~47nF in series with R2 , shelve filter~1nF from +in to comp pins, lowpassadd resistor 10k from S_V_MCU1will need adjust capacitor values to trim impulse response (no Vo overshoot)

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 13, 2021, 12:01:33 pm
content: thanks, i redraw it for tl494, since its 10times cheaper and i can get her almost everywhere...

author: strawberry
author_rank: Super Contributor
timestamp: December 13, 2021, 12:15:10 pm
content: R24 not to GND1nF -INemiter resistors need to be ~1k or less for decent turn off speed

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 13, 2021, 01:24:50 pm
content: Where to connect R24?TL494 controls gate drivers.

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 13, 2021, 03:58:47 pm
content: How to determine output caps value?charge = capacitence * voltage_changeCharge = curent_change * freewheel_time / 2Capacitence = current_change*freewheel_time/ 2 / voltage_change

author: strawberry
author_rank: Super Contributor
timestamp: December 13, 2021, 06:54:15 pm
content: C=(I*t)/VL=V/(I/t)design software ExcellentIT

author: prasimix
author_rank: Unknown
timestamp: December 14, 2021, 11:19:38 am
content: Quote from: MacIntoshCZ on December 10, 2021, 07:26:16 pmWhat's about SkyWorks (ex. SiLabs) Si823X series of drivers (0.5 or 4 A)?

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 14, 2021, 12:35:20 pm
content: thanks i will remember them =)Is this loop compensation OK if i would use both error op amps for current and voltage control of buck converter?

author: strawberry
author_rank: Super Contributor
timestamp: December 14, 2021, 02:17:14 pm
content: thats about rightINA280

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 16, 2021, 09:55:22 am
content: When i have wide output variable voltage, should i have more voltage dividers on output? And choose right divider with multiplexor for better voltage stability?Or i can do some substracting:0-50V output -> 0-2,5V50-100 output -> 2,5-5V minus 2,5V -> 0-2,5V100-150 outpit -> 5-7,5V minus 5V -> 0-2,5VWhat do you think strawberry?https://electronics.stackexchange.com/questions/502794/voltage-subtractor-using-op-amp***also there is option to do some level shift -> pwm output from mcu will control transitor conected to 7,5V reference. If tl494 op amp can handle that voltage and bet it can

author: strawberry
author_rank: Super Contributor
timestamp: December 16, 2021, 12:28:59 pm
content: 12bit DAC = 4095 speps or 36.6mV@150V, <100ppm feedback divider resistors recommendedcould use second DAC for fine adjustmentfeed both into summing opamp , one input for 100mV steps and other for 100uV steps, only TL494 opamp offset could be limitingfor high precision low offset opamps and LM399 referencecould use R2R DAC, need to match values to get reasonable accuracy, low pass filter not needed

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 22, 2021, 09:06:15 am
content: At the moment i have roughly layout of power part.I am also reading book about filters. Can i ask if you know how is those filters, i used for error op amp, called? I mean names of topology. No just lowpass / band stop filter. Thanks very much.

author: strawberry
author_rank: Super Contributor
timestamp: December 22, 2021, 03:06:14 pm
content: to design feedback filter need to calculate/measure powersupply phase and frequency response.powersupply power on , transient responseOP shelve and low pass filter

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 22, 2021, 04:14:11 pm
content: https://www.ti.com/seclit/ml/slup340/slup340.pdf?ts=1588283458920measuring is done without those filters?

author: strawberry
author_rank: Super Contributor
timestamp: December 22, 2021, 04:35:19 pm
content: transient response tests .. are done on completed PSUfor CV and CC mode separate testin prototyping stage filter can be trimmed/adjusted to get best performance

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 23, 2021, 02:11:03 pm
content: Should i add another op amp before tl494?I have output voltage conected from resistor divider to positive pin of op amp (they have negative pin).

author: strawberry
author_rank: Super Contributor
timestamp: December 23, 2021, 05:07:14 pm
content: for TL494 it depends CC or CE output connectionnegative feedback

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 23, 2021, 07:44:34 pm
content: Ok, thanks for help.Merry Christmas strawberry =)

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 30, 2021, 03:17:46 pm
content: I changed topology to half bridge and lower my requirements 0-150V 5A. I use precision op amp to be able to have 2mA -5A output.For reference voltage i use tl431D 1% precision.7V8 for 150V and , 5V6 for op amp 5,5V on 0,11R when 5A flowI used type 3 comnpensator for voltage and type 2 for currentI used 3 decoupling caps on outputs of potentiometers that sets voltage/current refence for error ampilifersI dont know if its right to use common collector output on tl494, if its bad selected output will be inverted.I would try differents types of control (as you mentioned with two adc connected together or pwm) but for beggining i would like to have no mcu

author: strawberry
author_rank: Super Contributor
timestamp: December 30, 2021, 06:26:08 pm
content: set_current set_voltage could share referenceu5b seems unnecessaryshort circuit protection?

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 30, 2021, 06:32:48 pm
content: i dont remember the reason why i picked 7v8 for 150V. I probably just selected random voltage under 10V, as high as possible for linear regulator.I used U5a with U5b for higher bandwith 3,3x3,3=10. Though i would get faster response.Short circuit protection would be done with regular fuse (primary and secondary). Or any other idea??

author: strawberry
author_rank: Super Contributor
timestamp: December 30, 2021, 09:34:42 pm
content: feedback bandwidth probably 1kHztransistors most likely wont survive fuse

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 31, 2021, 08:39:23 am
content: So Should i add current sense transformer on primary and another comparator and then feed output to input of the feedback pin of TL494.

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: January 01, 2022, 08:49:07 am
content: I am thinking about peak detector that will hold peak value until restart is done and comparator -> another error op amp.How fast reaction time should be? As fast as possible, i know =). How many cycles in terms of 1/fswitching is accetable? I´ve looked in datasheets of fuses, they are really slow...For op amps i would pick lm358, they have reaction time in terms of tens us...picture is from17:52

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 01, 2022, 08:55:15 am
content: Peak detection for what, metering? Controlling?Any kind of nonlinear element, not least of which a peak detector of some description, is almost certainly a terrible idea in the control loop. I don't know if this was intended.Why not run the TL494 in average current mode, and add a TL431 or other op-amp to perform voltage regulation?A Hall effect sensor on output inductor current is all that's needed to do this. Or just a low-side current shunt if it doesn't even need the isolation (which, I think this is common ground? so, this is a fine solution).Tim

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: January 01, 2022, 11:19:36 am
content: My idea is to add current sense transformer and low pass filter. Peak detector is used as "memory", with added comparator it will block pwm until someone turn psu off and on.But since i have current control on output, this will "work" only when fault happen when current loop is closed before shunt resistor. Broken caps, diode...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 01, 2022, 01:35:14 pm
content: Just move the shunt up in front of the caps. Close the loop on that first. First insight: inductor current can never be higher than the level it's programmed to. So just clamp the input level (coming from the voltage error amp). Boom, adjustable current limiting for free. And the response is vastly improved (both voltage and current loops can run faster than 1/sqrt(LC)). No worrying about startup, transient or fault current, it's always perfectly well behaved.You can put a CT on the primary if you like, but I don't feel it's very important at this power level. If something blows up, you need to take out the board, faff around with components, etc. regardless. Kinda, so what. And nothing is very expensive, a few bucks here or there to replace things. Not like it's industrial modules where a slip of the screwdriver craters $100 in fuses alone. (For which, desat protection is a valuable feature. Can do that too, if you want. But again, I wouldn't worry about it.)Tim

author: strawberry
author_rank: Super Contributor
timestamp: January 01, 2022, 04:47:12 pm
content: D13,D14,L1 larger to not saturate at secondary shortin this scenario maximum duty cycle could be limited(inductor must be discharged)

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: January 01, 2022, 05:32:59 pm
content: If i place current sense resistors on output before caps i should also add RC filter to remove current/voltage ripple. Should not I?When currents sense resistors are placed as they are at the moment current should be steady.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 02, 2022, 01:05:46 am
content: Nooo that adds tons of phase shift. The control needs the live value.Tim