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? enter image description here enter image description here

  • \$\begingroup\$ Read this answer and this question. There I present a link to a better BJT bridge that is able to handle 5A (with proper heatsinks) and does not allow the user to short the power supply (like Wouter implied). \$\endgroup\$
    – Ricardo
    Feb 27 '15 at 13:37

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?)

  • \$\begingroup\$ I haven't tried with both HIGH inputs. Why output voltage cannot be higher than input voltage? \$\endgroup\$
    – Thanawin
    Feb 27 '15 at 15:43
  • \$\begingroup\$ a) don't, just try to reason what will happen. b) google and read "emitter follower" \$\endgroup\$ Feb 27 '15 at 15:49

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