How to Convert a Power Supply from 20V,3A to 12V,5A by using UC3842?

[chirag2239]

Hi All,

I have a ready design of a power supply circuit and it is 20V,3A. But I need it to be done for 12V,5A. I have a design of transformer too which is for 12V,5A.

My switching frequency is 29KHz and have designed a transformer with the same switching frequency.

Please let me know, do I have to change any components except a transformer? If I have to change any component then please give me a calculation for that and let me know their values.

I am a beginner in SMPS design and I need some standard and unique key formulas to convert one voltage and current value to another voltage and current value.

Please help me as soon as possible.

 

[ArticCynda]

The primary components that need to be adjusted are
-transformer current capabilities => this is where a significant fraction of power losses will occur due to the parasitic resistance if the current increases
-output filter and capacitors => these will determine the ripple on the output voltage

If necessary, additional feedback from the secondary side (optically coupled) might be added for better output voltage stability and response.

 

[chirag2239]

Thanks ArticCynda.
I already have designed a transformer but I do not know how to calculate the values of the output filters. Can you help me to solve out this problem?

 

[goldsmith]

Hi All,

I have a ready design of a power supply circuit and it is 20V,3A. But I need it to be done for 12V,5A. I have a design of transformer too which is for 12V,5A.

My switching frequency is 29KHz and have designed a transformer with the same switching frequency.

Please let me know, do I have to change any components except a transformer? If I have to change any component then please give me a calculation for that and let me know their values.

I am a beginner in SMPS design and I need some standard and unique key formulas to convert one voltage and current value to another voltage and current value.

Please help me as soon as possible.

Hi

1- Redesign a transformer for this task .
2- Redesign the loop compensation .
3- Redesign the out put filter .
4- Redesign both current and voltage feedback networks .

I already have designed a transformer but I do not know how to calculate the values of the output filters. Can you help me to solve out this problem?

That is a Flyback converter hence L6 is negligible and you can remove it too but if you want to use it you can use the former value which it had .
C6 and C7 must be selected by the ESR and di and dv formula which can be easily founded in any kind of text books or articles which are dealing with switching power supplies . have a bit search if you couldn't find then ask it again here .
Good luck
Goldsmith