Controlling negative voltage with +5 logic
- From: hondgm@xxxxxxxxx
- Date: 3 Aug 2006 17:20:00 -0700
I have a situation where I have to control a small 24V fan with +5V
logic. This would be simple using an N-channel MOSFET. The problem is
that the fan must be powered with the -24V supply. Everything uses a
common ground.
I have come up with the idea of using an N-channel, connecting the
source to -24V, connect the fan to the drain and ground. Then drive
the gate through a zener so when the logic output is at 0, the 24V
difference isn't enough to cause the zener to breakdown, but when the
logic output switches to 1 (+5V), the 29V difference is. I also have a
zener across the gate and source so I don't excess Vgs. This setup
doesn't seem very robust.
Is there another, simple solution I'm overlooking? No relays please,
and I'm trying to avoid opto-isolators.
.
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