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50V, 50A H-Bridge IC needed


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oh yes, sorry, I never worked with p-types before.

I made the changes and it did seem to work better.

When I switched to the 24V SLA though, it melted again. It did seem to take about half a second this time rather than being instant as before. The heat sink is pretty big so it can't be that.

The test coil I was using has a resistance of 2.8 ohms and an inductance of a few mH. So at most the current should be about 9A.

There are two things I can think of to check. One would be to test the circuit with a resistive load to see if it is somehow the inductance causing the problem. The other thing will be to check the voltage drop on the battery as if it goes too low, the gates wont switch properly.

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The battery voltage drops to 22 when I connect the coil directly, so this should be fine.

I replaced the MOSFETs, and I've noticed that the circuit draws some current even when no load is connected. If I put the 4k7 resistors across the zeners, it stops this happening.

Could the values of R2/4/5/6 need changing?

(PS they are 12V zeners)

I've not removed the low side zeners yet as I think they are doing nothing right?

I really appreciate your help, I'll send you something nice when its working!

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It makes no difference unfortunately. I've even tried just pulsing bridgeA and leaving the other off. The high side MOSFET still gets hot quickly.

For example using a 1R resistive load, 24V input (drops to 22V)  from an SLA. Pulsing to give avearge current of about 9A. After 10 secs, low side measures 25C and the high side measures 85C and rising. (I'm measuring the front of the case rather than the heat sink)

So, now it is only pulsing a resistive load and in one direction. When I've use single n-types, such heating would make me think it is not fully on, or has a high on state resistance. The datasheet says 0.06 ohms, so average power dissipation should be just 5W.

I want to try manually holding the high side on, then pulsing one of the low side ones to see if the same heating occurs. For the P-type, do I need to make it about 10V lower than the source pin rather than 10V higher as you would in an N-type?

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I just had a better look at the final circuit. The zener voltage is too low which makes me think that you are operating them far away from the zener region. As suggested, reduce R2,R4. You can also measure and include in your resistor calculation the C-E saturation voltage of Q1, Q2 although that will be tiny compared with Vpower-Ground.

Also in a previous post you say that you will keep a high side on and pulse the low sides. Careful, you will blow a pair up on either the first or second pulse.

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