How to generate 22V pulses from TTL and a 22V supply

Discussion in 'General Electronics Discussion' started by Andymitchell, Apr 30, 2012.

1. Andymitchell

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0
Apr 30, 2012
Hi Forum users,
I am having trouble updating a circuit. The current circuit uses a TC4427 Mosfet driver with TTL input and 18V supply voltage to generate 0.5 to 2 usec 18V pulses.
Now I need to generate slightly higher voltage pulses,22V this time. Unfortunately this is outside the range of the TC4427 (I've confirmed this by burning a few out)
So does any body know how to increase the voltage of my pulses. The duty cycle ON:OFF is about 1:100 to 1:1000.
My limitation is that I have a TTL source to trigger the pulse, but I can supply the 22V, no problem. It seems a simple problem to solve but its got me stumped
Thanks for any ideas...
P.S. I am slightly naiive electronically speaking even though I have developed several hundred digital circuits.
Andy

2. BobK

7,682
1,688
Jan 5, 2010
You need a level shifter. Depending on the current you need out, this can be as simple as an NPN with the emitter to ground, the collector to a resistor to 22V and the base to a resistor to the TTL signal. If you need to source significant current, you will need to follow this with a PNP high side switch.

Bob

3. GonzoEngineer

321
2
Dec 2, 2011
How much current do you need to source and sink?

4. BobK

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1,688
Jan 5, 2010
And how fast does it need to switch?

Bob

5. Andymitchell

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Apr 30, 2012

I don't need to draw much current, maybe 50ma peak but much less than that on time average. I will build a test circuit with an npn and hope it is that simple. As far as speed goes I would be aiming for rise and fall times of no more than 100nsec.
Andy

6. BobK

7,682
1,688
Jan 5, 2010
50ma is a lot of current. You can't use the simplest (single transistor) version for that. For example, if you used a 100R resistor, that would drop 5V at 50ma. So you would need a level shifter followed by a push-pull pair. To make this out of discrete transistors it would be difficult to get the 100ns rise and fall times. I think you should look for a MOSFET driver chip that can handle the 22V.

Bob

7. Andymitchell

3
0
Apr 30, 2012
22v pulses

The suppose this is where my problem began. The tc4227 that I have been using is a MOSFET device. But this can only be used up to 18 volts, I'm having trouble finding something that will work at 22v. I have tried to use capacitors and diodes to add pulses as in a Dickson multiplier but have only managed to get a distorted and not very useful pulse out. I expect that this was not the right thing to try. I will have another search on mosfets .
Thanks
Andy