Driving a 12v DC motor

[foTONICS]

So I was trying to build an hbridge for a 12v dc motor using 2n3055's and was having issues so I decided to break it in pieces and do some testing. Attached is the circuit I tried and it doesn't do anything. Someone told me that I need a high side driver to get it to work. Am I right when I think that only 4.3V is being dropped across the motor? Would I need a base voltage of 12.7V for this to operate correctly? Could I get around using a high side driver circuit by using a darlington transistor or is it a voltage problem?

 

[foTONICS]

Just thought of something, wouldn't 12.7V make the collector base bias wrong?

 

[BobK]

1. That is not an H-bridge.
2. There is no reason to have a transistor or each side of the motor.
3. There needs to be a current limiting resistor between 5V and the base(s)
4. The emitter of the transistor on the left will be at about 4.3V, dropping most of your 12V supply and giving the motor about 4V.

What is it you are trying to do?

Bob

 

[foTONICS]

I know it's not an H-bridge, I was having issues getting the full H-bridge working so I took it apart to see if I could get parts of it working but still no success. Since then I have figured out to get the motor the 12V I need a high side driver.

I looked up the values of hfe of the mje3055t and the specs varied greatly (between 20 and 70) for base currents under 4A (which I will be using). So when selecting the resistors that will be driving the transistors should I value them for the lowest hfe to ensure full saturation or should I shoot for an average value?