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Product Guides and Tutorials

Power Pulse ModulatorPower Pulse Modulators

This tutorial is for our dicontinued models and nolonger applies to models currently on sale

Adding Soft start and stop to your PWM

When switching on a motor, there is often a large 'kick' as it suddenly accelrates from a stationary position. One way to avoid this is to use what is known as a "soft start". This is where the output duty will gradually increase from 0% to whatever value you require over a predetermined time. Typicaly this time would be just a fraction of a second.

This article explains how you can add a couple of components to the connectors of our power pulse modulators so that you can achive a soft start and soft stop output.

Soft Start and Stop Connections

The diagram above represents the connections needed to set up a PWM-OCB with a soft start/stop switch. The usual connections to the power supply are not shown for simplicity. This can be done with any of our PWM models.

All that is needed is a resistor, capacitor, and a small toggle switch. The switch (SW1) is attatched in place of the jumper marked PWM so that switching it will make or break the connection between the jumper pins. The resistor (Rt) can be connected using the terminal connections at the end of the board and should connect between PWM and V+. The capacitor Ct should connect between PWM and GND.

The value of the capacitor and resistor will determine the speed of the soft start/stop function. The resistor should be at least 100k otherwise the output duty will not be able to reach 100%. A typical value for the capacitor Ct would be about 10uF.

Note that when you first apply power to the circuit, the duty will start at 100% and then settle to zero. Once settled, you can use the switch SW1 to switch the output on or off. The output will rise to whatever value is set by the duty control pot.

We suggest using a 10uF Electroyitic Capacitor and a 100k Resistor.

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