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Electronics => Projects, Designs, and Technical Stuff => Topic started by: RawCode on March 31, 2022, 01:34:12 pm

Title: Varying open-drain pull-up voltage for pulse generator
Post by: RawCode on March 31, 2022, 01:34:12 pm

Hello everybody.

I would like to develop in my circuit a small variable pulse generator, with user-customizable pulse width and amplitude (say 1-100ns pulses over 0-5V).
The idea was to use the timer output (open-drain 5V tolerant) of an SMT32 to generate the pulse and then use the STM's DAC to set the pulse amplitude.
Here follows the circuit diagram that I was thinking of.

 [attach=1]

I tried to build this circuit on a breadboard, but once I connect the timer output (TIMOUT) to the voltage rail (BUFOUT) with a 100R resistor, both signals go to zero.

Probably I'm doing something wrong with my breadboard, but what do you think about this idea and this circuit?
Do you have any suggestions to improve this design?
Thanks :)

Title: Re: Varying open-drain pull-up voltage for pulse generator
Post by: jonpaul on March 31, 2022, 01:41:20 pm

C1 C2 short circuit output
Should be from Vcc to ground
j

Title: Re: Varying open-drain pull-up voltage for pulse generator
Post by: RawCode on March 31, 2022, 01:48:47 pm

Quote from: jonpaul on March 31, 2022, 01:41:20 pm

C1 C2 short circuit output
Should be from Vcc to ground
j

Sorry, probably I'm missing something, but I put C1 and C2 to have some sort of "storage" at the buffered DAC's output and make the pull-up voltage as stable and stiff as possible with such fast switching signal.
Why do you say that C1 and C2 short circuit the output?