Need help for SEPIC Converter

[samson.bunty1986]

Hi all,

I have designed Sepic converter which can give output 24V,2.5A. In simulation am getting all correct values.  I made PCB with that circuit. But now when i connect load my ouput voltage drastically dropping to 8V. Kindly help me out from this

Thanks in Advance

[Hero999]

Apart from the fact, the circuit is wrong, you need to change C1 from an electrolytic to ceramic capacitor.

[samson.bunty1986]

Here is my circuit. How can you say my circuit is wrong?? Please suggest me..

Thanks in advance

[Hero999]

Good, you've realised you won't get any help, unless you give enough information.

Are you sure the simulation is accurate?

Have you assumed ideal components?

What about the PCB (which again you've not posted so we don't know)? Is it correct. Have you followed the layout recommendations of the SMPS IC manufacturer?

[samson.bunty1986]

Hi Hero,

Thanks for you reply.

In LT Spice i hve checked.. it is accurate. But now on PCB am not getting.

Kindly suggest me about the Layout recomendation. I hope evry thing i made.

Regards,
Samson

[Hero999]

In LT Spice i hve checked.. it is accurate. But now on PCB am not getting.

What I meant was are you sure the models used are accurate?

For example, have you included the ESR of the inductors and capacitors? If the the answer is no, then your simulation is wrong.

[samson.bunty1986]

Ya..i have used all the parameters in simulation. The same components  used on PCB also.

[Hero999]

How are we supposed to help you with the #pcb when you haven't posted the layout or a photograph?

Is the PCB layout similar to that given on the datasheet?