I am attaching a motor to an ATmega32 chip. I want to build an H-bridge but before doing that, I want to control the motor using the chip. I bought few NPN Transistors from RadioShack. I have 5V running though the breadboard. I attached Vcc to the Collector, Base to the Pin, and Emitter to the motor. And other wire of motor is hooked up to Ground. Unfortunately, the power coming out of the transistor is too low, the motor is barely moving (As opposed to when I hook up my motor straight to 5V). What is wrong? Do I need a different transistor or is my setup wrong? If it is the transistor, can you please recommend the right one, I am not too good at those.
Electronic – Using a transistor as a switch
atmegaavrbreadboardtransistors
Related Solutions
As Matt says, the first thing that jumps out is more capacitance needed.
Breadboards are terrible for stray inductance/capacitance so you really need to try and keep wires as short as possible, keep sensitive signals away from higher current/voltage/fast changing signals, and add plenty of bypass and bulk capacitance around the circuit.
I would start with a couple of >100uF electrolytics on each power rail and near the FET, with a few 100nF or higher ceramic caps on the power pins of the ICs.
Another thing to look at is using a separate rail for the relay, and routing the ground return separately from the uC's ground. Of course they need to be tied together, but you can ensure the high current return does not flow through the uC board's ground this way.
The two leads of the motor are shorted together so no matter the state of the transistors, the current will always flow around the motor instead of through it.
For example, if the "Switch Motor" signal is pulled HIGH, then the current completely bypasses the motor as shown below:
When the "Switch Motor" signal is pulled low, nothing happens. The base of the upper transistor is reverse biased, so it is in the OFF state and no current flows. Unless you meant for that transistor to be a PNP instead of an NPN, then current would flow from 5V to GND but it would still bypass the motor. Either way, the result is no motion from the motor.
I recommend studying how a classic H-bridge functions. They're relatively simple circuits, and doing so will also teach you about flyback diodes to protect your circuit. Here's a good explanation.
Best Answer
As already noted, the direct connection of a NPN BJT (or N-channel Mosfet) in high-side configuration is not suitable (emitter follower no saturates with equal voltages Vb and Vc). A proper driver is required. For example these ones on figure below (B, instead uses a PNP):
(A) Input Low -> load On; Input High -> Load Off
(B) Input Low -> load Off; Input High -> Load On
The problem with (A) is the initial state under power-on or reset by watchdog activation. Maybe, in some application, can be a bonus.