NNTP-Posting-Date: Mon, 16 Dec 2002 05:10:57 -0600
From: firstname.lastname@example.org (John Fields)
Subject: Re: switching Mosfet dilema
Date: Mon, 16 Dec 2002 10:47:47 GMT
Organization: Austin Instruments, Inc.
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On 16 Dec 2002 02:44:17 -0800, email@example.com (james armand)
>First time user of MOSFET. Anyone who faced the same problem?
>I have a rated current of 46Amps and a voltage of 43vdc delivered by a
>battery. I want to switch on and off the flow of current. I thought of
>using relays but they may generate sparks. So I thought about a
>However, I need to have a device to control the source/drain voltage.
>I connected my Drain to the +36. My Source to a load and I use a
>+5vdc/0vdc to switch on/off my device.
>Is this going to work? or what are the issues I should be addressing?
>Any other possibilities to consider?
If you're using an enhancement mode N-channel MOSFET and you expect
the +36V to appear across the load with 5V on the gate, it won't
work. Consider that the gate voltage has to be 5V above the source
for the MOSFET to turn on, and you can see that since the source is
connected to the load, as the voltage on the load increases, the
voltage on the gate will also have to be increased to allow more
voltage to appear across the load. The easiest way around this is
to connect one side of the load to +36V, the other side to the
drain, and the source to ground/battery-. If you have a logic-level
MOSFET you'll be able to use 5V on the gate to turn it on, but if
you don't you'll need something more like 10V. check the data sheet.
You also haven't said anything about what kind of a load you're
driving, so there may be many more issues which need to be
Professional circuit designer