Help with H-bridge IC

[Kaets]

Hi all,

I'm trying to make a DC/AC inverter using a MOSFET H-bridge and an INTERSIL ISL83204A full bridge driver IC. So far I've almost got the circuit to work - three of the outputs form square waves, but one of the high side outputs (BHO) won't turn off.

While the three working outputs alternate between 0V and around 15V, the fourth just stays at about 10V - not fully on, but high enough to cause the MOSFET to turn on and short circuit the power supply.

I'm assuming it doesn't get to 15V because there's no 'off' state to power the bootstrap circuit, but I can't work out why it won't turn off.

It seems odd that only one output is misbehaving. Can anyone think of a reason why this would happen, or does it sound like the driver IC is faulty?

Any help much appreciated.

Matt

 

[Triode]

Could you sketch or otherwise show how you have it set up? Maybe a photo? It's very hard to guess by description of the issue alone.

 

[Kaets]

Hi Paul, thanks for the reply!
I'll draw up a circuit diagram ASAP.

One thing I thought was that the driver chip has 4 inputs that are taken from the sources of the MOSFETs. In the diagram on the data sheet, there's a resistor between the lower MOSFETs and ground, which would make the inputs from the lower two FETs greater than 0V, but I left that out of my circuit to maximise current through the load (the data sheet diagram is for hysteresis switching - not sure what that means but i'll be just using a square wave input).

I bought another couple of chips to see if I'd broken the first one, and I tried adding small resistors after the lower FETs. All the outputs worked, so i tried removing the resistors again, and found that two of the outputs stopped working. Adding the resistors again didn't fix it so I obviously blew the chip again.

Any ideas why that would happen? Could it be that the source inputs can't handle being driven to 0V?

Like I said I'll draw up a diagram of what I'm doing as soon as I can.

Cheers

 

[ronv]

ALS and BLS should be tied to ground, but that doesn't sound like your problem. You have trouble with the high side.

 

[Triode]

That sounds like an oddly fragile chip, it's true you shouldn't hook them up wrong because it can blow them out, but most are designed to take some abuse.