H-bridge Problem - Electronic Circuits Projects Diagrams Free

ahmad-al3omar · 29th April 2008, 07:34 AM

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

ericgibbs · 29th April 2008, 07:40 AM

Quote:

Originally Posted by ahmad-al3omar

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 · 29th April 2008, 08:17 AM

Quote:

Originally Posted by ericgibbs

hi,
Post the design for 2*npn and 2*pnp version so that we can check the circuit.

DESIGN.jpg

this is the siple circuit

ericgibbs · 29th April 2008, 08:29 AM

Quote:

Originally Posted by ahmad-al3omar

Attachment 19002

this is the siple circuit

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.!

positronicle · 29th April 2008, 08:39 AM

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.

ahmad-al3omar · 29th April 2008, 08:45 AM

Quote:

Originally Posted by ericgibbs

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.!

the signal 5v with 20mA current and the motors operates at +12 volts and 1A current

ericgibbs · 29th April 2008, 08:55 AM

Quote:

Originally Posted by ahmad-al3omar

the signal 5v with 20mA current and the motors operates at +12 volts and 1A current

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.

Analog · 29th April 2008, 12:12 PM

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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29th April 2008, 07:34 AM	(permalink)
ahmad-al3omar	H-bridge Problem 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

29th April 2008, 08:39 AM	(permalink)
positronicle	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.

29th April 2008, 12:12 PM	(permalink)
Analog	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. __________________ "Everything that is done in the world is done by hope." -Martin Luther "There are two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."-Albert Einstein