DC Motor Controller for PCB Drill

Published on June 09, 2016 . Updated on: -
This is a simple circuit that can be use to vary the speed of a DC motor. It is very useful for controlling a PCB drill, but it can be used for whatever applications you want. The speed can vary from full to complete stop. The circuit is versatile and can be used with motors of different currents and voltages.

This circuit is widespread on the internet. Here is an example. The PWM signal is generated by a 555 chip. The chip drives a MOS-FET transistor that will switch the motor on and off. The 555 is powered from a 7805 regulator. Therefore, the motor DC voltage can be between 8 and 35 V (the circuit can be powered by AC 7...26 V). The maximum current is limited by MOS-FET.

The circuit shown here is designed to be AC powered by a mains transformer. But you can power it from a DC adapter, battery or even a computer power supply if you remove the diode bridge and connect the power lines straight to ground and positive pads, where the output pins of the bridge would otherwise fit.

DC Motor Controller for PCB Drill 555

This is the schematic. Remember that you need to use a power source capable of supplying enough amps for the motor. If you will be using a transformer and a high current motor, change the diode bridge with a suitable one. Also use a MOS-FET with higher current rating.

DC Motor Controller for PCB Drill with 555 PWM schematic
DC Motor controller with 555 schematic
When the resistance between cursor of R3 potentiometer and D3 diode decreases, the duty factor of the PWM signal increases and motor speed increases. I used a 2SK2382 MOS-FET because I had it lying around, salvaged from an old computer monitor. This is an old model and although it can withstand 15A, there are newer types with better characteristics. Look for one with a drain-source voltage at least 2-3 times greater that the supply voltage of your motor. The same for amperage if you use a heatsink. Be sure it has a gate threshold voltage lower than 5 V.

The 7805 regulator doesn't need a heatsink. C4 should have at least 1000 uF and a correct voltage rating depending on the supply voltage. C1 value is not critical. Anything greater than 47 uF will be just fine.

555 PWM Output
Output PWM signal at different potentiometer values
Here are my PCB designs. The top photo shows a simpler version without D2 and C1. Don't forget there's a jumper below the IC!

555 Motor controller PCB
Motor controller PCB
The PCB size is 30 x 81 mm. The tracks that need to withstand higher currents are thicker.

Downloads: PCB as PDF.

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