I want t build a DIY speed controller using a BD139 transistor. The motor needs to be powered by 3.7 V to operate. In some cases (youtube tutorial,) it can be used for 12 V DC motor. How can I build one for 3.7 V DC motor?

I'm newbie in electronics. I'm going to learn it from forums like this. This is a DIY ESC (electronic speed controller) project for my DIY Arduino drone. The output of the ESC is 3.7 V to power a 720 DC brushed motor (a kind of brushed motor from Syma X5C).

I already did one using a TIP122 + 10 kΩ resistor + 1N4007 diode, but the RPM ca not reach the real RPM as the datasheet. Besides, the speed is not stable.

I have triple check the software of the drone, the wiring and everything is okay.

enter image description here

Talking to many forums, the problem is the ESC. That's why I ask a question related to the title in this forum.

The point is: How can I build an ESC for a brushed DC 720 motor using a BD139? Are the components that I need the same as with the TIP122 above?

  • 1
    \$\begingroup\$ Where's the datasheet for the motor? What makes you think the BD139 is a suitable transistor? What input do you want to for the controller? What control do you want? how many speed levels do you want? do you want to control direction as well? What type of motor is it? We need a lot more information here. \$\endgroup\$
    – Puffafish
    Commented Aug 15, 2023 at 16:19
  • 5
    \$\begingroup\$ I suppose one could do that. But this is equivalent to asking "Build a car using this steering wheel". You haven't exactly given us a lot to go on here. \$\endgroup\$ Commented Aug 15, 2023 at 16:19
  • \$\begingroup\$ I want to build a diy esc for 3.7 volt. \$\endgroup\$
    – ArduJimmy
    Commented Aug 16, 2023 at 2:43
  • \$\begingroup\$ What is the motor rated for? \$\endgroup\$ Commented Aug 16, 2023 at 4:23

1 Answer 1



simulate this circuit – Schematic created using CircuitLab

ESC with BSS138

I simulated the motor with a 1 mH inductor (L1) and 20 ohm series resistance. Reliable switching requires at least 2.5-3 volts on the gate, for this MOSFET model.

There is also some considerable turn on/off time which will be important if you are using PWM.

I see that the TIP122 is actually a Darlington, which should switch OK with 3.7 volts on the base, but there will always be about 0.7 volts drop. This may be OK, depending on motor characteristics.

Here's a simulation using TIP122, with a 20 kHz PWM drive.


simulate this circuit



  • \$\begingroup\$ Thanks so much for your answer. I will try it first \$\endgroup\$
    – ArduJimmy
    Commented Aug 16, 2023 at 11:04
  • \$\begingroup\$ I still use TIP122 with in4001 (not in4007 as I did). YOU save me, brother. My drone finally flies after spending 3 years. \$\endgroup\$
    – ArduJimmy
    Commented Aug 16, 2023 at 22:01
  • \$\begingroup\$ Here's the demo to take off: youtube.com/shorts/Kc6fk2Emhc0 \$\endgroup\$
    – ArduJimmy
    Commented Oct 5, 2023 at 14:24

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