Simple Pulse Generator Has Low Parts Count

Abstract: With a few op amps and some external components, you can build a pulse generator with variable frequency and duty cycle.

The natural choice for generating a pulse of variable frequency and duty cycle is a good bench-top pulse generator. If you don’t have a generator or must build one into your system, however, you can do it with a few op amps and some external components (Figure 1).

U1 and Q1 form a voltage-controlled oscillator (VCO) with a square-wave output and a triangle-wave output. The square wave feeds back to control the charge and discharge of integrating capacitor C1, and is also useful as a sync-signal output. The triangle wave drives the non-inverting input of duty-cycle controller U2-2. R2 fully adjusts the output duty cycle (from 0% to 100%) by controlling U2-2′s inverting input. U2-2 generates the output signal directly.

U2-1 buffers R1′s wiper voltage, which controls the VCO frequency. A change in supply voltage (V+) varies the output swing without effecting the output frequency or duty cycle, and the circuit operates equally well with a single supply or with dual supplies. The frequency range shown is 20Hz to 13kHz, but you can modify that range by changing the value of C1. The dual op amps (designed for controlling power amplifiers) are chosen for their high output drive, rail-to-rail input and output capabilities, single-supply operation, and exceptional open-loop behavior.

This entry was posted on Tuesday, July 10th, 2007 at 9:28 am and is filed under oscillator generator. You can leave a response, or trackback from your own site.

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