Half-bridge heat problems

[chimi]

Hi, I finally succesfully built an off-line 250W Half bridge SMPS using as driver an IR2110, didn't blow up or anything taking the nessesary cautions...
Thing is, I correctly snubbed the FETs' switching noise with 2 RC snubbers (sorry, the only snubber I know for this topology), and the err amp compensation is ok (works fine in full range of voltage/current) but still in the DC side, the diodes (four MUR460) heat up pretty fast, even at low current, while the mosFETs (2SK2645) at 100W output, even with no heat sink, don't get even at 50ºC, I can touch them with no problem... Is the riging left that is making the diodes heat up so much? I've tried first with schottky rectifiers (MBR2045CTG) with big heat sinks, and looking at the transformer output I thought it might be because of the secondary voltage wich is 38V+ringing (approx 43.5V peak) so I changed them for the MUR460s, but the result is the same... I know the UF diodes are much slower than schottky rectifiers so... Will it make any difference placing MBR20100 instead? or I must reduce the ringing even more?

I attached the signal in 300V side and the rectified signal before the inductive filter

Thanx!

[chimi]

Here's the secondary signal before the output inductor

Cheers!

[Tahmid]

Hi,
Please post your circuit so that it is easier to find out the problem.
Thanks.

[luka]

Hi

Waveforms don't look too bad, this would heat diodes enough

[Tahmid]

Hi luka,
I am not very good at analysing waveforms. Could you please explain to me how you arrived at your conclusion?
Thanks in advance.

[luka]

Hi

Had same waveforms, but no heat, ok not that bad, but there should be something done, maybe something with trafo, since there is way too much ringing to start with

[edfed]

maybe the high side mosfet is not properlly driven.

it is a big problem to drive this floating GS junstion, and that's why i use a hand made transformer to drive the two mosfets.

how to do this driver?

very simple and easy:
take a toroid, build one primary with 10 turns, and as many secondaries as you have mosfets to drive with the ratio 1:1

put a 10k resistor before GS junction.
put clamping diodes on primary winding.

then, it will be a very simple cheap transformer.

[areza]

chimi , may be there is a small asymmetry present at secondary winding, there is some overshoot present at primary side , use a snuber across primary and across diodes , redothe transformer, make the windings interleaved – P-S-S-P,

[Tahmid]

Chimi,
Your circuit is not a difficult one but driving with ir2110 requires some knowledge. Please post your schematic, so that we can sort out the problem.
Thanks.

[Tahmid]

Edfed,
Why transformer? I think IR2110 works with no problems and chimi has done it. If there is any problem, he can try to overcome and if he posts his schematic, the problem can be sorted out.