Help, Schmitt trigger - Page 2 - Electronic Circuits Projects Diagrams Free

Roff · 28th January 2008, 10:08 PM

Quote:

Originally Posted by rngd

Actually, the main circuit is someone else's and I'm just trying to figure out how hysteresis adjustments are made.

OK sorry, forget the equations, can you just tell me what the reference voltage at the negative input does ?

When it is at the positive it affects the Vin, what about at the negative ? I cant find anything about it either online or in books...

I don't know why you say that. Vref does not affect Vin in either case. In fact, Vin is by definition a voltage source, so it can't be affected by Vref. Here are the equations for -in and +in Schmitt triggers.

rngd · 29th January 2008, 10:42 AM

Sorry, I meant it affects the input to the positive/the UTP value.

Ok, thanks very much for the analysis (again).

rngd · 29th January 2008, 06:32 PM

Ron, is there a typo for the +in calcs ? The second box, at first its Vutp then you change it to Vltp.

Roff · 29th January 2008, 06:37 PM

Quote:

Originally Posted by rngd

Ron, is there a typo for the +in calcs ? The second box, at first its Vutp then you change it to Vltp.

Nope, that's the way it works out when you switch from -in to +in. I ran simulations with an LM393 just to make sure my equations gave me the same answers as did the sims.

rngd · 29th January 2008, 07:23 PM

Weird though, in my circuit there is no Rth. Cannot be that the Vutp, Vltp and Vref are at the same voltage point .. ?

Roff · 29th January 2008, 08:10 PM

Quote:

Originally Posted by rngd

Weird though, in my circuit there is no Rth. Cannot be that the Vutp, Vltp and Vref are at the same voltage point .. ?

See the annotated schematic below. Note that Rth and Vref change when you change the pot setting.

rngd · 25th February 2008, 03:51 PM

heh, I got so busy I forgot to thank you for your help. Thanks very much Roff !

Roff · 25th February 2008, 04:09 PM

Quote:

Originally Posted by rngd

heh, I got so busy I forgot to thank you for your help. Thanks very much Roff !

You're welcome.

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29th January 2008, 10:42 AM	(permalink)
rngd	Sorry, I meant it affects the input to the positive/the UTP value. Ok, thanks very much for the analysis (again).

29th January 2008, 06:32 PM	(permalink)
rngd	Ron, is there a typo for the +in calcs ? The second box, at first its Vutp then you change it to Vltp.

25th February 2008, 03:51 PM	(permalink)
rngd	heh, I got so busy I forgot to thank you for your help. Thanks very much Roff !