0-50V 0-10A Variable SMPS

[fethiyeli]

Yes, also, i think the datasheet of LT124X does say that LT124X are pin for pin compatible with uc384x series.
I think the UCC38c4x series is also the same but draws less bias current, so you may prefer it.
Remember also you only need the 50% duty one as its 2TFC.
There is also the NCP12XX series which may do the trick.

Thats good news. I am gonna try to simulate with LTSpice. Yea i know, in 2T forward, above 50% duty cycle must be avoided in order not to saturate the main transformer. Thats why also i used UC3844 giving 50% duty cycle at most. I have taken 40% duty cycle at most in transformer calculations. Yea there are many alternatives for pwm and pfc ics but the problem is that we can not find them easily here. So i did select the common ones.

 

[fethiyeli]

Yes, also, i think the datasheet of LT124X does say that LT124X are pin for pin compatible with uc384x series.
I think the UCC38c4x series is also the same but draws less bias current, so you may prefer it.
Remember also you only need the 50% duty one as its 2TFC.
There is also the NCP12XX series which may do the trick.

I tried to simulate in LTSpice but i encountered with annoying floating problems as always. Thats why i hate all simulation software. U can download the files at attachment. :bang:

 

[treez]

sorry I don't have RAR file unzipper...I just tried to download a free one and it instead gave me some PC care software instead.
Maybe you should change the solver to "alternate 2", or "skip initial operating point"
Yes you cannot have floating nodes, you need to connect a ground, or connect a ground via a 10meg resistor say if you wish

 

[fethiyeli]

sorry I don't have RAR file unzipper...I just tried to download a free one and it instead gave me some PC care software instead.
Maybe you should change the solver to "alternate 2", or "skip initial operating point"
Yes you cannot have floating nodes, you need to connect a ground, or connect a ground via a 10meg resistor say if you wish

Ok man thnx. I will try your solutions and give u feedback tomorrow. I can make the files as txt file so you can download and see.

15.7kB Draft1.txt = Draft1.asc
564 bayt Draft1 (2).txt = Draft1 (2).log
5.75kB Draft1 (3).txt = Draft1 (3).raw
2.84kB LM324.txt = LM324.mod
2.39kB LM324_test.txt = LM324_test.asc

 

[treez]

Ok I had a quik look at draft and you did not pick mosfet, you just put a fet symbol, you should pick an actual device or else it doesn't work. Also, I think you should use GND only and not "common". I also see you still use the 10u cap.

 

[fethiyeli]

Ok I had a quik look at draft and you did not pick mosfet, you just put a fet symbol, you should pick an actual device or else it doesn't work. Also, I think you should use GND only and not "common". I also see you still use the 10u cap.

Ok thanks a lot. Yea i forgot to pick a mosfet. I used common since between gdt and main transformer must be isolated. I ll write the results tomorrow. Thnx.

And is there any disadvantage to use 10u cap ? If yes, then ofc i ll use the smaller one in value.

 

[treez]

yes you cannot get a true copy of the primary waveform with the 10u cap there...if you see the sim I sent to you, compare that with the one where you have 10u.

 

[fethiyeli]

yes you cannot get a true copy of the primary waveform with the 10u cap there...if you see the sim I sent to you, compare that with the one where you have 10u.

Yes, you are right. I was not able to get true waveform of primary when i chose 10u cap but 330p cap is used to filter the spikes. For normal operation 330p is used in parallel with 1 - 4.7u cap. I always see such combination. But in LTSpice, when i use 10u cap it gives me a voltage up to 130V and not DC output.

By the way, although i changed the grounds, it didnt work. I also pick a mosfet for 2T forward and i think i am never gonna learn how to simulate correctly.

 

[treez]

I woul RC filter the voltage across the "burden" resistor, not put a cap in parallel with it.
Simulation you only learn by trial and error. Sometimes my 100th simulation attempt works, the first version never works.

 

[fethiyeli]

I woul RC filter the voltage across the "burden" resistor, not put a cap in parallel with it.
Simulation you only learn by trial and error. Sometimes my 100th simulation attempt works, the first version never works.

Thnx. In another forum, they say that i need to put dummy load at both SMPS and PFC outputs and maybe also need for flyback outputs. Do i really need these resistors and is there any specific calculation for them ?

 

[treez]

yes, dummy load is V(out)/(Load current)

 

[fethiyeli]

yes, dummy load is V(out)/(Load current)

I have seen in a SMPS handbook, they use 1k resistor for 0-60V 0-5A output. But i cant put a 50V/10A = 5R resistor, it will waste of power. Maybe 1k resistor is suitable. It is common to draw a few mA from output i think. So if i put 1k, 50V^2 / 1k = 2.5W at most.

 

[treez]

as you know, the sim wont waste power like that, your circuit will, but I guess you have to test it on full load anyway, so please go ahead

 

[fethiyeli]

as you know, the sim wont waste power like that, your circuit will, but I guess you have to test it on full load anyway, so please go ahead

Ok thnx. I will give you feedback.

 

[treez]

ok, I send you here good knowledge on current sense transformers...simulations etc

- - - Updated - - -

also, I send here a novel two transistor forward converter simulation etc...its simple and doesn't need gate drive transformers

 

[fethiyeli]

ok, I send you here good knowledge on current sense transformers...simulations etc

- - - Updated - - -

also, I send here a novel two transistor forward converter simulation etc...its simple and doesn't need gate drive transformers

Thnx a lot man.

The schematics below are the final ones.

 

[treez]

**broken link removed**

The above (page 13-15 gives good knowledge on boost diode and fet for pfc...Infineon do an excellent range there, you could also use there EICE driver to get the gate turn off lop small, rather than the pnp.

I trust you used the power.com software to design the topswitch one. I think its called PIexpert.

- - - Updated - - -

I didn't see your opto feedback to uc3842...it should go to comp pin of uc3842, and fb pin should be grounded

 

[fethiyeli]

**broken link removed**

The above (page 13-15 gives good knowledge on boost diode and fet for pfc...Infineon do an excellent range there, you could also use there EICE driver to get the gate turn off lop small, rather than the pnp.

I trust you used the power.com software to design the topswitch one. I think its called PIexpert.

- - - Updated - - -

I didn't see your opto feedback to uc3842...it should go to comp pin of uc3842, and fb pin should be grounded

Thnx for infineon app note. Yea i used PIexpert for flyback converter for supply.

UC3842 and PFC stage does not share same ground. I dont need a opto feedback. No need for isolation. Mine is similar to circuit below. Every supply, output are isolated from ac line.

http://danyk.cz/reg60v_en.html

 

[treez]

sorry but no you are using mains input...you need optocoupler or similar to give isolation, otherwise its very dangerous.
UC3842 and PFC surely share same ground...I mean, pfc provides vin for uc3842, they need same ground

 

[fethiyeli]

sorry but no you are using mains input...you need optocoupler or similar to give isolation, otherwise its very dangerous.
UC3842 and PFC surely share same ground...I mean, pfc provides vin for uc3842, they need same ground

UC3842 has GND but pfc has earth symbol. They dont have the same. Isolated VCC supplies to UC3842 ( i am gonna use uc3844 ) so there is no requirement for opto or isolation. Take a closer look to flyback supply.