Switch selection for H-bridge design

I'm trying to design an H-bridge that can control the output polarity of an electromagenetic coil with inductance of around 50mH and very low resistance. The source voltage is around 150V at 40A and hence the design and, particularly, the switches aren't trivial.

The timing constraints make things even tougher - the circuit needs to be able to switch within a few ms of the control signal trigger going high. One switched, the circuit will stay in the same polarity for around 100ms or so. Hence, it's far more about response time and lag than it is about actual switch frequency.

I've considered both solid state relays (IGBTs and MOSFETs) as well as electro-mechanical relays. The solid state stuff seems to have considerable power losses due to the voltage drop between emitter and collector. The electro-mechanical relays suffer from being too slow and/or occasionaly bouncing when driven hard (which is likely to blow my PSU)

Does anyone have any suggestions for a good solid state solution that has low power losses, or an electromechanical solution that is fast enough and wont bounce?

 

Thanks for all the replies, very helpful.

It's very interesting that you mention IXYS - I used an IXYS MOSFET and dirver combination in a pulsed-laser diode PCB I made. However, that doesn't make me an expert as I based my design on the data sheet reference circuit!!

Resqueline - your post got me thinking. Timing is very important to me as I want the switch to make the circuit to within +/- 1ms of a target time. However, I will get at 100ms advance notice of when this time is and hence I could pre-fire the switch to hit the precise time as long as the lag of the switch was consistent. If so, then this might bring electro-mechanical relays back into the picture. Maybe the lag varies though? Also, might I get problems with the contact bouncing?

 

Hey Steve,

Yes, I agree - it will take 13 ms to charge. This is not a problem, however there needs to be tight control over when the 13ms charge period actually begins. This was the main problem with using a relay which might take 50ms or more just to close the contact.

I was talking about predicting the beginning of the charge period and hence switching the relay 50ms in advance to negate the lag, but I think there are other issues with relays too (such as bouncing).

Clearly a mosfet could achieve the response required, provided I could live with the power dissapation - 72W for each switch normal (2x simultaneous required in normal h-bridge operation) is a real downer in the context of this experiment.

I'm guessing though that this is the final word - either live with the approx 70W power disappation of a solid state solution or put up with the timing and bouncing issues of an electromechanical solution?

 

Very interesting idea indeed!! Plus the IGBT thing is something I hadn't considered at all. I assume that there are pros and cons to IGBTs vs MOSfets?? (as you can see I dont know much about them).

I wanted to have a quick look at the link you posted but it doesn't work - looks like there is a few letters missing.

CORRECTION - it works fine, I'm the idiot by trying to cut and past the text into a new browser (which didnt work obviously).