- Controlling a dc motor with 2n2222a transistor driver#
- Controlling a dc motor with 2n2222a transistor full#
I got a multi pack of rectifier diodes, a lower voltage motor, and picked up one of the reed relays erco mentioned. It it were me, I would use a FET instead of a transistor.Well I swung by the shack today and picked up some parts. However 350ma continuous through a 4401 without a heat sink is stretching the limits a bit. I have run a 2N2222 at 200 ma continuous (driving a brushless 12V computer fan motor) with no problems. This is why I suggested 5 seconds on and 5 seconds off. I would not reduce the resistor to less than about 120 Ohms.Īlan is correct about the heat dissipation in the Transistor. Keep reducing the resistor value and recalculating until you get to 12 to 15 ma.
You could then reduce the resistor to 220 ohms and measure and calculate again. For example, you measure the I/O Pin voltage to be 3.3 volts and you have a 330R resistor.ģ.3 Volts Volts divided by 330 Ohms means there is about 10ma of current through the transistor base. You can get a good idea of the base current by measuring the voltage at the I/O pin and using Ohms Law. If the motor still does not run after testing with the example circuit, you can reduce the base resistor to as low as about 180 ohms. The voltage always sags under a load and this affects current. The PIC/Picaxe does not lend itself to simple calculations for output pin current. However it may be a good idea to provide more current to assure that the transistor is fully on. With a worst case gain of 40 you will need a minimum of about 8.75 ma of current at the base to just barely get to 350ma. Per the spec sheet the motor is rated at 12V/350ma.
Controlling a dc motor with 2n2222a transistor driver#
That motor doesn't really look very suited to speed control, but perhaps something could be done with a PNP emitter follower (dissipating lots of power) or a PWM power supply configuration (requiring an additional inductor to maintain a dc voltage on the brushless driver circuit during the "flywheel", or energy recovery, phase). The maximim rating for that transistor (without a heastsink) at "room teperature" is only 0.625 watt, so it might not work for very long! But that gain is specified with two volts across the collector-emitter, which means that the transistor could be dissipating one watt. The (minimum) current gain of the 2N4401 is 40 at 500 mA so the (nearly) 10 mA through the resistor should be just about enough. However, Goeytex's configuration should at least work (if you haven't mis-wired and/or destroyed the transistor), but probably not very well. Some incorporate an H bridge which permits both foreword and reverse rotation.Ĭlick to expand.No, it's because you wired the transistor as an "emitter follower" which has unity voltage gain, so the motor would not "see" more than about 4 volts (at best) from the PICaxe. They take standard hobby servo inputs (see SERVO and SERVOPOS commands), and output PWM to the motor.
One easy way to implement DC (or even brushless) motor speed control is to use commonly available hobby type ESC's. The torque developed by the motor will reduce in proportion to current (PWM minimises this effect). The transistor will act like a resistor, so will get hot in proportion to the voltage drop x current Motor speed can certainly be controlled by controlling current using a transistor. PWM can be very easily implemented using a Picaxe. Selecting an appropriate FET and driver is a whole new ball-game. A transistor drive can also be used, but will have a small voltage drop (around 0.6V) when fully on. A dedicated chip to drive the FET gate is often used to deliver the high instantaneous currents needed to quickly turn the FET fully on and off.
Controlling a dc motor with 2n2222a transistor full#
A FET is often used as the driver since their on resistance is low, and they can deliver very close to full supply voltage. The duty cycle of the pulses (on time to off time ratio) controls the motor speed. The motor is fed with the full voltage pulsed at a frequency typically 500 to 3000 Hz. The most common method of controlling DC brushed motors is by using Pulse Width Modulation (PWM).
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