T&L Publications

Hi All
I want to switch a voltage (100-150VDC) with current possibly as high as 4amps using a microcontroller and/or a user selectable switch. The voltage will be distributed to 4 separate circuits and each should be selectable independently. Does anybody have a circuit that can do this? I was considering MOSFETS but not sure which type would be best? Also, can I run this voltage/amperage through a PCB and, if so what size should my traces be? Voltage switching will be intermittent (not on all the time) and, when on will be under 3 seconds or so.

Thanks for any help

I am not sure exactly what your project requirements are but since you said microcontroller *and/or* switch...

A uC may not be needed. If you get a 4 position rotary switch (or 5 if you want an off position), you could use 12v for the switch to control 4 relays. This would be much more straight forward. It does depend on what you want to do, exactly.

Hope it helps,
Kevin

reletive to a 5V, 100uA chip, 150V, 4A is high but compared to other stuff, 4A, 150VDC is not in the category of high voltage. There should be plenty of FETs with VDS >200V, and ID >4A (probably NMOS Enhancement mode would be best). Just search by parameter on a site like Digikey.

Now you shouldn't expect to turn that FET all the way on with just 5V VGS so you're going to need a level shifter circuit between your low voltage control circuit and the high voltage driver output section. There are purpose built ICs called FET drivers that could work and there also discrete passive circuits that can pull up the gate voltage as well. Take a look at the family of curves in the datasheet to estimate gate drive voltage you will need.

As for trace width. It isn't just a rule of thumb, you need to consider allowable voltage drop and temperature rise and if it is an inner layer trace, how long it is etc. In any case, just google "PCB trace calculator" and you will find lots of them. This is the first one I looked at and using mostly default values in his calculator I get 150mil trace at 2 OZ copper will get you a 5V drop at 1 inch for example. Just plug in numbers and see what you get.
http://www.desmith.net/NMdS/Electronics/TraceWidth.html

Thanks for the replies.
The mosfet approach should work and the traces don't turn out to be as wide as I was thinking so should be good.
I will probably use a rotary switch to keep it simple