trouble with bipolar transistor h-bridge

Development Boards Arduino
1

I’m trying to drive a motor using a bipolar transistor H-birdge (built according to the schematic at http://www.robotroom.com/BipolarHBridge.html.

I don’t have any specs on the motor. Instead of the motor turning, one of the transistors just gets hot. I have tried changing the base resistor values around and so far all it has done is change how quickly the transistor gets hot.

Any suggestions?

2

any suggestions?

Yes, give more details. What type transistors? Double, triple checked the circuit? Voltage applied? Resistance of the motor coil? How are you controlling the transistors?
3

Perhaps you are turning on the two right or left side transistors causing a short? As #5 said “Need Input”.

4

The polarity of R2 and R4 in that diagram are also reversed - to turn them on set the output to LOW. R1 and R3 are turned on by setting to HIGH.

If the supply voltage is too high, it’s not possible to turn off the PNP transistors because the voltage difference between the emitter and base is high enough to keep it on. Normally, the PNPs are driven by NPNs to avoid that problem.

5

Sorry for not providing more detail. Like I said, I have it wired up just like the linked article shows (and have verified this multiple times). I am using +5v (regulated from an Arduino) to power the rails on my breadboard. The transistors I am using are basic 2N2222As and 2N2907s from RadioShack. I don’t have any details on the motor at them moment, but can check after work. At the moment I am directly applying +5v to R3 and GND to R2 from the respective rails on the breadboard to try and get it to work.

I know for sure the motor itself will run off +5v and is not bad, although I do not know the resistance; I will check that as soon as I can. I am able to drive the motor either by connecting it directly to +5v and GND or by using a 2N2222A on the ground to control it with the transistor (either by a switch or with the Arduino).

6

Are you sure that the diodes are good, and installed the right way around?

Which transistor gets hot?

7

I measured the resistance of the motor (straight across the leads with a multimeter, right?) and it read about 27ohms.

I also just finished pulling the whole breadboard setup apart again and redoing it EXACTLY like it is in the article (down to the pin spacing). This time, it worked. I guess I must have been missing something the past few gos. :oops:

Thanks for the help, folks! (I promise, that isn’t sarcasm… I just figure it could come off that way by mistake.)