modified 8 years ago

Flip flop SCHMITT TRIGGER needs sorting out -help seeked...

00:53:22

SCHMITT TRIGGER

I need a schmitt trigger made from discrete components because the use of 1/6 of one 74HC14,is absurd!

However this is the best I have been able to come up with even tho the input impedance is quite low compared to the chip versions.

It might work but it suffers from mark space ration problems, low input impedance and it doesn't quite square things up very well..

Can anyone provide insight ?

Obviously I do expect the trolling buggering slag-off attitudes that come from a few nasty minded personnel here at EC but it would be nice to think that one might get a real answer.

Actually its the first time I've asked for help directly!!!!!

73

published 8 years ago

Bushmills

8 years ago

Multivibrator style Schmitt triggers are characterized by resistors between transistor emitters and ground. Try EC search function, search for Schmitt trigger, there ought to be plenty discrete examples. I'd probably use an opamp with feedback on the non-inverting input for the hysteresis instead.

zorgrian

8 years ago

I wanted to avoid using integrated circuits

zorgrian

8 years ago

I cant see that multivibrator style Schmitt trigger circuits are characterized by resistors between transistor emitters and ground...?

roops1967

8 years ago

All you need is 6 fets for an inverting... http://everycircuit.com/circuit/6433203137282048

zorgrian

8 years ago

Yeah thanx but, in this case if possible im looking for a BJT implemented circuit that WILL run at 7 MHz and up... I have tried everything that appears on EC already. This flip flop circuit is the closest approximation to what i want. I remember seeing something with BJTs and diodes many years ago in a magazine. However, I've forgotten how that worked. Possible advancing years, failing eyesight and other personal problems... Who knows... I know there is a simple solution. Just can't remember it.

zorgrian

8 years ago

@bushmills, putting resistance between emitters and ground only degrade the wave shape at RF. Unless you can post a link to your idea i just don't get you...

zorgrian

8 years ago

If i put 6 fets in the mix, i may as well use a 74hc14

roops1967

8 years ago

Here's the raw component layout for the schmitt you're talking about. Now it's up to you to tweak the biasing an resistors...

roops1967

8 years ago

http://everycircuit.com/circuit/4896673175437312

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