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DC motor speed controling Answered

I'm trying to mod my Tascam cassette recorder. I want to be able control speed of the motor.
So I bought on ebay PWM controller and after installation thing don't run so smooth as I wish.
the problem is ... when pot is all the way down at 7 clock motor is off, when I turn it to 8 a clock motor starts spinning and reaches its full speed at 9 a clock. and from 9 a clock to 4 there is no effect on speed.
Please help me! .... my electronic skills are too weak to understand this.


it is 12v dc motor and there is link for the pwm I use.




Hi Josehf!

Thanks for this simple circuit. In your post you saying "there is little chance of burning out the motor" how big is this chance ?

Also I only have a933 and c1740 transistor, Can is use them?

Thanks for your help

Well the LM7812 is a 1 amp 12 volt regulator and the BC517 is a 1 amp NPN Darlington Transistor in that configuration it assures you get 12 volts but limits your amperage to control your motor speed.

The 2SA933 Is a PNP Transistor 0.15 amp so the motor cannot draw more than 0.15 amp and I think that motor draws 0.2 amps loaded.

You gave me the idea of trying that circuit with a PNP transistor.

The 2SC1740 is an NPN Transistor but it is also 0.15 amp and as I said the motor is 0.2 amp loaded.

A BC337, BC517, or a BC635, would be best, you might be able to get away with 2N3904, a 2N4401, or a 2N2222, as long as you don't exceed 0.6 amps.

You can get datasheets here:


And here you can get the datasheets with partial numbers:


Sorry missed the little chance.

If you lower the voltage to slow down a motor the current goes up and it is the current that burns out a motor.

In this circuit the voltage is fixed but the current is lowered to slow down the motor so burning out the motor is almost non existent.

Thanks for everything Josehf, it was very informative and helpful.

I'm not sure what current it draws... there is the specification of my motor

  • EG-530AD-2F 12V DC Motor
  • Voltage Range (VDC): 8.4-15
  • Current (Amps): 0.073
  • Rated Speed (RPM): 2400
  • Torque (g-cm):8
  • Part number : EG-530AD-2F ( EG530AD2F

Well it said 0.075 amps.

The 2SC1740 is 0.15 amps it should carry the motor.

Thank you


2 years ago

That control you bought is an overkill for a cassette recorder.

Joe has a simple analog control for you.