H-bridge Problem

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ahmad-al3omar

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dear all;
i have power transistors (tip122 -npn- ) and (tip126 -pnp-) in order to make a high rating H-Bridge i tried to use the four npn transistors in one design and to use two npn and two pnp in another one but there allot of problems , the motor rotates in a very low speed and on of transistor burned how can i come over these problems without using a single H-Bridge chip .
thank you
 

hi,
Post the design for 2*npn and 2*pnp version so that we can check the circuit.
 
ahmad-al3omar said:
View attachment 19002

this is the siple circuit
Click to expand...

hi,
The diagram shows -12V as the supply to the bridge, is that correct.? EDITED:

Also, what are the signal levels at 'A and B'.?

EDIT: If I magnify the drawing I can just see the +12V, in normal viewing it looks like a minus sign.!
 
Last edited:
Your transistors would probably benefit by adding a schottky diode to their outputs. While it won't help any speed issues you may be having, it will more than likely extend their life.
 
ericgibbs said:
hi,
The diagram shows -12V as the supply to the bridge, is that correct.? EDITED:

Also, what are the signal levels at 'A and B'.?

EDIT: If I magnify the drawing I can just see the +12V, in normal viewing it looks like a minus sign.!
Click to expand...
the signal 5v with 20mA current and the motors operates at +12 volts and 1A current
 
ahmad-al3omar said:
the signal 5v with 20mA current and the motors operates at +12 volts and 1A current
Click to expand...

hi,
When 'A' is high [+5v] the motor will only have about 3 or 4V across it.

Added protection diodes to the circuit.

EDIT: updated drawing showing some approximate voltages.
 
Last edited:
You show each leg as a class B output stage, like in an amplifier. Classic H bridge designs have the pnp on the highside, and npn on the lowside. I would actually trash this whole design and go with mosfets. Use a p channel on the highside and n channel on the low side to avoid using a charge pump. You did not mention the amount of current needed.
 
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