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Please let me know your idea about this circuit

Masoud Torabi

Apr 17, 2015
18
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Apr 17, 2015
Messages
18
Hi every body.
dears I want to make a circuit that its input is TTL and its output alternate between zero and 24V. I make one but it doesn't work properly .
I attached it and its wave form. green wave is for V1 and blue is output(Q3's voltage ).Untitled5.jpg

please analyze it and let me know my mistake. I start to change the circuit but I like know why this circuit doesn't work. because I reach to desire wave form in simulation with orcad.
and if you have better idea let me be aware your idea.

Untitled4.jpg
 

duke37

Jan 9, 2011
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5,364
You have four waveforms on the scope, is this actual voltages or simulations.
The two pairs of waveforms have vastly different time bases, what is the red square?

The top waveforms look reasonable with the output sinking slowly, being pulled down by R4.

A simulation will assume that the supply is rigid at 24V, in practice the voltage will vary with current drawn. Good power supply bypassing is essential with fast pulse circuits.
 

Masoud Torabi

Apr 17, 2015
18
Joined
Apr 17, 2015
Messages
18
You have four waveforms on the scope, is this actual voltages or simulations.
The two pairs of waveforms have vastly different time bases, what is the red square?

The top waveforms look reasonable with the output sinking slowly, being pulled down by R4.

A simulation will assume that the supply is rigid at 24V, in practice the voltage will vary with current drawn. Good power supply bypassing is essential with fast pulse circuits.

it's the actual waveform by digital oscope. red square zoomed waveform that is located in down of image and shown it bigger in upper pair.
 

garry

Apr 18, 2015
5
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Apr 18, 2015
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5
It looks like the output voltage is not dropping fast enough. When Q1 turn off, V1 goes to 28V turning Q3 off. This should allow C1 to discharge through R4. The CR time for this should be about 0.2us, the scope trace show the CR time is much longer.

Try removing the capacitor and checking the components you have fitted for C1 and R4.

Let me know if my understanding of your circuit is correct.

By the why do you need C1? this will just slow the falling edge of the pulse.
 

BobK

Jan 5, 2010
7,682
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Jan 5, 2010
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7,682
I think the problem is that these transistors do not respond fast enough for 10nS pulses. Set it to 10uS and see if it improves.

Bob
 
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