Controlproblems with a SMPS-Converter

[wackerchen]

Hello, I designed a SMPS-converter, now I have the problem that my first test, the test if the control-circuit fails.
The circuit is nothing special, the IC is a SG3525. As an attechment I added the control-circuit and the SMPS-circuit.
When I test the control-circuit my problem is, that during the measurement with an oscilloscope this influence in the behavior of the circuit takes. It is definitly not a soldering-problem, I checked it several times.
Perhaps there is a mistake in the design and I don`t see it.

Thank you very much for hints.

 

[TheOne]

It would fail as you are trying to drive 2 gate's of which one is referenced to -ve and the upper switch at 1/2 DC bus potential. You need a drive transformer from the control IC to the fets. One winding on the IC side and two windings (phased correctly) on the fet's side. Search Philips, SGS micro-devices etc. for application notes using isolated gate drive. Otherwise you can get IC's made for driving upper and lower fet's in 1/2 bridge converters.

 

[Sebi]

And what kind of rectifier with FETs? In this position need a dual schottky rectifier.

 

[TheOne]

It is called a synchronous rectifier, more efficient than diodes especially at high frequencies