one shot using nand gates

simon christoforidis

Hello from Australia!

I need to make a one-shot to reset a Programmable Unijuction Transistor for a Ramp Generator.

The reset is needed to syncronise with the other part of the circuit.

In theory ,all I have to do is put the incoming CLK through a NAND gate with the other input (2 inputs total),connected to the inverse

of the Q output through a charging capacitor which charges via Q through a resistor.

The 'Interlock' is suppose to stop the incoming CLK from holding to flip/flop high.

But the circuit 'Oscillates' at around 3Mhz and I don't know why?

It seems like a straight forward circuit.Does anybody know of an easier way to make a one-shot in a DIP package?

Thanks-Simon

0 Avi Chami1 over 11 years ago

There are many ways to make a one shot, including using the old venerable 555... Do you mind to post your circuit?

Best regards,

Avi

0 simon christoforidis over 11 years ago

This is the hand-drawn circuit for the one-shot.Hope it helps.

Thanks-Simon

0 Avi Chami1 over 11 years ago in reply to simon christoforidis

http://www.electronics-tutorials.ws/waveforms/monostable.html

0 simon christoforidis over 11 years ago in reply to Avi Chami1

I found out why I'm having so much trouble with this circuit oscillating, is the fact that

Flip-Flops are ambigious (oscillate), when I try and set and reset at the same time!

As I mentioned before ,I'm looking for a shorter pulse than I originally put in, and so

far the only way to do it is to use an Op-Amp and set it to the narrow section of the

High-pass filter input ,therefore getting a Buffered output with enough current to

set a Programmable Unijuction Transistor.So far its the only narrow One-Shot I can

think of.

Thanks for your help

Simon

0 Andy Neil over 11 years ago in reply to simon christoforidis

Guru 35525 points

As already suggested, why not just use a 555 ??

0 Brian Boorman over 11 years ago in reply to simon christoforidis

Guru 25210 points

simon christoforidis said:

is the fact that

Flip-Flops are ambigious (oscillate), when I try and set and reset at the same time!

This is called meta-stability. It's why flip-flops have setup and hold time requirements.

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