Re: switching FETs or relays
- From: bill.sloman@xxxxxxxx
- Date: Sun, 02 Sep 2007 16:19:29 -0700
On Sep 3, 6:38 am, "Mis...@xxxxxxxxx" <Mis...@xxxxxxxxx> wrote:
I want to run my amplifier via batteries and use a TTL driven switch
to turn it ON, only when it's needed - to save power. So for +/- 12
volts with 20 mA should i go with FETs or just used mechanical
switches?
A couple of MOSFET switches are going to be cheaper, more compact and
much less power hungry.
Using a TTL output (switching between 0.4V and around 3.0V) to control
a P-channel MOSFET sourcing your +12V and an N-channel MOSFET sourcing
your -12V is going to take a little fiddling.
A 1k pull-up resistor from the TTL output to +5V would give you useful
extra output swing.
You could use a "logic level" N-MOSFET - gate tied to the TTL output,
source tied to 0V and drain tied to the gate of the P-channel MOSFET
to control the +12V rail. You will need a resistor (perhaps100k) tied
to the +12V supply to make sure that the P-channel MOSFET turns off.
Turning on the -12V rail is a little more difficult. Perhaps the
easiest way to do it would to use a second P-channel MOSFET in
parallel with the one switching the +12V rail to drive the gate of the
N-channel MOSFET driving the -12V rail. Again, you will need a
resistor from the drain of the second P-channel MOSFET to the -12V
supply to make sure that the N-channel MOSFET is fully off when it is
supposed to be off.
Hope this helps.
--
Bill Sloman, Nijmegen
.
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