DC-DC Converter

[Joe Wu]

Hi, I have recently built a dc-dc converter to convert supply voltage from 6V to 32V, the circuit diagram is as below:

 

and the circuit on the breadboard is looks like this:

 

My friend has built one with the same circuit diagram, I have double checked with him, both circuit connects exactly the same with same components, he circuit is working perfectly fine, but my circuit has a problem. my output voltage jump to the 42V, slowly drops to 32V, jump up again to 42V, slowly drops and it repeats this process over and over again. I have no idea what is wrong with it.

 

Here is how my friend circuit looks like:

 

Any help will be appreciate!

 

Thank you!

 

[audioguru]

Your attachments do not work. Usually a circuit built on a solderless breadboard with messy wiring all over the place and intermittent contacts does not work.

I have designed and built thousands of prototype circuits, some VERY complicated, soldered together on a compact stripboard layout and they all work perfectly.

Your voltage jumping at a steady low frequency indicates "motor-boating" low frequency positive feedback. It might be a part that fails when it heats (overheats?) then works again for a while when it cools.

Your attachements are actually links to All-About-Circuits where we must join to see them. Instead attach them here to your replies.