# Positive and negative pulse amplification circuit

Discussion in 'Electronic Design' started by captoro, Apr 23, 2013.

1. ### captoroGuest

I have a circuit composed of Lm393 with 12v power supply.
I can output two synchronous pulses: +12v and -12v
I would like to put a coil between so I get a 24v difference.
Taking the positive side and hooking it up to the coil and a mosfet after the coil.
Can I use the -12v as my drain on the mosfet ?
I dont want to blow anything up so thats why I am asking what would be best way to do this. I also heard that i needed to one mosfet for positive and one mosfet for negative side ....
any ideas?
thanks

ken

2. ### JamieGuest

Trying to picture that in my head, Is that a cascode config
you're after?

Jamie

3. ### captoroGuest

how do you post an image here ??

k

4. ### captoroGuest

I'll explain a bit better:

I have two LM393 with a 12v power supply.
One of the LM393 is outputting pulses at +12v and the other LM393 at -12V.
I would like to pulse a motor with that 24v difference.
Obviously I cannot drive the motor with the LM393.
So I thought of pulsing n-channel mosfet to drive the motor.
If I had only the positive side to take of I would connect the drain to the motor and source to ground. What is confusing me is that I have a virtual -12v ground. How do I drive a motor with the 24v difference (+12v to -12v) ?

K

5. ### whit3rdGuest

If you want 24V, why not use a 24V power supply on the LM393?

The outputs are good for 6 mA (guaranteed) current, and
are 'off' half the time, so you'll get less than a tenth watt for
your motor (at 12V) . Will that be a problem?

An oscillator and coil, with tap, can make any voltage you'd like
(the Ford model A got kilovolts from a 6V battery this way).

6. ### JamieGuest

If you have a virtual ground to give you a -12 volts, then that means

Turning on the fet is simple, use an R to your virtual ground to the
gate, connect the source to the -12 supply leg. when the comparator
is in the off set, meaning the open collector is not on, the gate
common R will switch the FET on. This is because the source is sitting
at a -12, which looks like +12V at the gate if the source was on the
common, Of course you need the open collector to also be connected to
the gate along with the virtual ground R.

THe motor can be connected to the Drain of the Mfet while the other
pole is connected to the +12V. This will give you the 24 volts to the
motor while splitting the rail via a v-ground for the rest of your circuit.

Basically you only need one comparator sitting on a split rail, when
the output is off, the gate R to common will turn on the MFET.

of course this does not give you a bridge so if you are thinking about
reversing the motor, then you need some more semi-conductors.

Jamie

7. ### Phil AllisonGuest

"John Fields"
** This is our old friend "lerameur".

Making sense is not part of his modus operandi.

My take on his latest insanity is that he wants to drive a 24V DC motor
using a 12V DC supply by feeding the motor with pulses of alternating
polarity.

Motor will act like mule.

.... Phil

8. ### Jasen BettsGuest

You'll need more than just that to get 24V from a 12V supply.