Power Chopper Tester

This little handy circuit produces pulse width modulated output according to the position of the potentiometer. It is great for testing the power chopper without having to rig the whole chain of transmitter, receiver and controller. 

It uses the 555 timer chip in the astable mode. When the output at pin 3 is high, C1 charges from the upper part of the pot.  When output goes low, C1 discharges through the lower part of the pot.  Current blocking is done by the diodes.  The duty cycle can be varied from very nearly 0% to nearly 100% with very little pull in frequency.  It can also accept voltages from about 5V up to 15V.  With the values of components as shown the rate is in the 10Khz to 15Khz.  This can be reduced by adding more capacitors in parallel with C1, or increasing the resistance of the pot. Higher rates can be achieved by using a smaller C1.

The actual output has been taken from pin 7 and this requires a pull up resistor. The output may be improved by adding a buffer, or by paralleling several CMOS buffer gates. Note that this circuit is intended to test only the power chopper part of a speed controller it cannot be used to test normal speed controllers as these expect to see pulses in the range of 1 to 2ms spaced by about 20ms.

When coupled with a power chopper, the circuit finds many applications where the speed of a DC motor, light intensity of lamps, heating elements etc, has to be adjusted manually.

Last modified on 25 May 2000