Building a Pulse Generator
centage of time that Q2 remains at a high-level voltage). For the transistor shown, it will deliver 500 mA
at a 10 percent duty cycle with no degradation in
pulse specs. For an example, a 2N3904 would deliver 100 mA under the same conditions.
For U6 (CMOS to TTL translator), I used a hex
inverter only because it was handy. Any TTL gate
configuration is suitable; just make sure the output
remains non-inverted with respect to the input.
Upon completion, if you encounter problems,
start by checking the power supply sources (+ 15
and + 5 volts). Then look at rate generator U4 to
make sure it is running. U4 will run when U2a-P9
is positive and stop when it’s negative. Beyond
the generator and due to circuit simplicity, you can
go stage by stage using standard troubleshooting
techniques.
When you finish this project, you will have a source of
pulse generation capable of a wide range of outputs:
Figure 4. The power switch is located on the back of the case.
Trigger — continuous, single burst, internal or external
Output — adequate drive for virtually any circuitry (zero to
14 volts, peak)
Rate — continuously variable from two microseconds to
one second
Width — continuously variable from one microsecond to
one millisecond
Personally, this was an interesting and fun project to
build and has proved to be an essential piece of gear to my
test bench. Take your time building this, do a professional
job, and you will be as satisfied as I am. NV
APRIL 2005
Circle #135 on the Reader Service Card.
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