Half bridge smps voltage drop problem

[subwo1]

One thing I don't like about transformers is that they seem to need low impedance drive themselves if they are not to load down the control circuit output. I don't like winding them either. I guess they would be OK with most of the standard controller chips which can drive MOSFET gates directly, anyway.

I like the IR2113's CMOS inputs, too. It also has enough instantaneous current ability to drive the hefty IRF7343 buffers without increasing rise and fall time. Small transformers are a problem with regard to creepages and circuit placement, IMO, too.

[subwo1]

Originally posted by Eva
...power it...

I do like this advantage, though.

[N-Channel]

Alex,

All this talk about your supply has re-ignited my interest in re-assembling my old SMPS. Thing is, in trying to remove the '740s today, I broke the gate terminal off one of them. My last Motorola IRF740 has gone the that big MOSFET in the sky! I do have a couple rails of MTW20N50E lying about. At 20A and 500Vdss, with 240mW Rds(on), I guess I will use two of them.

Joe, the gate capacitance of the MTWs varies from 3900pF to 7000pF. Do you think I should look into the source-follower buffer you mentioned?

Steve

[MOER]

We do our off line supplies a little differently. We use TL494 driving a set of PNPs which drive a small gate drive xfr. Regulat half bridge configuration for the main switchers. We do not use TO220 fets bur rather IRFP360N. These are more robust than the smaller guys.

Advantage of the use of the drive transformer is that my TL494 can be at audio ground potential (It is always driven by a small houskeeping transformer) We apply full balanced feedback from our secondaries which allow us to keep the output voltage constant whether loaded or not. The seondary used a common mode choke and the transformer is wound to give about a 25% overwind ratio. Feedabck resistors at the TL494 set the final value of the output

We have used the IR2113 chips, nice but no isolation. Opto coupled feedback is required but this does not allow us to have the perfect regulation we have with balanced feedback.

At 62KHz the transformer you want to use with the amount of power you want is way to small. Check the charts on the Magentics web site

Steve

[subwo1]

Originally posted by N-Channel


Joe, the gate capacitance of the MTWs varies from 3900pF to 7000pF. Do you think I should look into the source-follower buffer you mentioned?

Steve

Steve,
I think probably yes. In a standard type design (not ZVS) for efficiency, it can be good to have extra drive, especially to turn off the MOSFETs quickly because that is when they dissipate maximum power. Also, you can be more confident that you won't blow your IR211x MOSFET driver if you should decide to experiment with the circuit. If you would like me to clarify anything about adding the IRF7343 buffers, feel free to ask since I am not sure if any information is available from other Internet sources.

MOER,
thanks for relaying that information. It is good to see what has worked well for others, especially with regard to future work in which we might like to try new things, or if we encounter a problem which something we read about on the forum might solve.

[Workhorse]

Hi Folks,

Try this link offline smps of pulse series amps from Crown:

http://www.crownaudio.com/pdf/legacy/s-c650as-03.pdf

K a n w a r

[Eva]

That's straightforward non-regulated half-bridge stuff. However, I like how they are reading the analog temperature sense signals with a PIC that does not have any ADC input (I use the same trick)

[Workhorse]

So Eva tell us that secret trick please...something from your magicbox.....

[Eva]

It's very straightforward, try to figure out first...

[Workhorse]

OK got it they have used LM35 precision temp sensor along with TL072 as comparator to get high/low output for the PIC to read...correct me if iam wrong....

K a n w a r