H-bridge problem with TIP122.

arduinoh-bridge

I tried to make H-bridge by TIP 122 transistor.
I used 9V for a VCC. I used push button to control H-bridge, and it's fine.
Then I used Arduino 2560 with two digital pins for driving H-bridge. But the output voltage was only 5V. And also, I tried with VCC= 15V, output still be 5V.

Could you please give me an advice?
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Best Answer

The upper TIP122's are wired as emitter-followers, so their output voltage can never be higher than their input (base) voltage. (In fact it will be ~ 2 x 0.6V lower.)

When you fed the inputs with the full Vcc that was not much of a problem, but when you feed it with the 5V Arduino outputs you will get no more than 5V from the outputs.

One solution is to put a level shifter between the Arduino outputs and the H-bridge. But it will still be a crappy H-bridge. (Do you realize what will happen when you make BOTH inputs high?)

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