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Square-wave generator.



This is a simple square-wave generator for measuring slew-rate on amplifiers.
It is built on a piece of strip-board and is powered from a 9 V battery.


Square-wave generator schematic.
Fig.1: Schematic.

U1 is a 5 V regulator.
U2 is an astable multivibrator built around a Schimdt-trigger.
U3 is a divide-by-2 that insures a 50% duty-cycle.
The inputs to the unused gates in U2 and U3 must be connected to GND/VDD as shown.
The 100 nF capacitors must be ceramic types. All other components are non-critical.
The output voltage between OUTA and GND or between OUTB and GND is 4.5 V-pp.
The output voltage between OUTA and OUTB is 9 V-pp.
If the output voltage is too high, reduce the values of R4 and R5.
The output frequency is approximately 0.6 / ( R1 * C6 ) ( 10 kHz with the values shown ).
The output rise/fall times is 35 ns with no load, but will increase with any real-world load.

Amplifier input example schematic.
Fig.2: Amplifier input example.

When driving an amplifier input as shown in fig.2, the rise/fall times measured between the IN and GND terminals are increased to 1.1 µs.
With an amplitude of 4.5 V-pp, this is a slew-rate of 3.3 V/µs ( 0.8 * 4.5 / 1.1 ).
If you need higher slew-rate, replace U3 with a CD74AC74 and reduce the values of R2 and R3.

Photo of finished circuit.
Fig.3: Photo of finished circuit.

Never apply high level square waves to multi-way loudspeakers. You will burn the tweeters.

Poul Petersen, C/Faya 14, 35120 Arguineguín, Las Palmas, Spain.
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