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H-bridge driving problem

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ZynT

ZynT

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Hi there;

I've designed an h-bridge.
It is normal when i use for only one direction unless connect the other port.
This means that when i connect the IC to only R2, (R1 is not connected)
when this port is +5V, motor runs.
when this is 0V, motor stops. There is no problem.

Problem is that while connect other port and it is reverse of the other.
situation is this:
to R2 is +5V, to R1 0V. Motor doesn't turn. (or vice versa)
Also, R3 and R4 heat up.

I couldnt see how current flows. Can anybody do?

Circuit is driven L297.

**broken link removed**
 

Just try this driver circute it works fine.
 

Well let's just go ahead and see the problem to your circute,you mention R3 and R4 heat up when you reverse the input? What is the value of R3 and R4 you used and I dont think you need 0v in your circute therefore the two diode you used is not necessary.
 

Your transistors have 18v power supply in the collector but they can only output 4.3v in the emitter
because you drive them with 5v in an emitter follower configuration so the emitter will be 0.6v-0.7v lower than the base voltage.
The 4.3v going to the gate is very low.

Alex

---------- Post added at 00:33 ---------- Previous post was at 00:18 ----------

Also the two diodes in the input seem to short-circuit the output of the transistors (emitter) to the 0v (gnd)
or is that connection something else.
Why do you have 0v and gnd separately drawn?
If you drive the transistors with a higher voltage the circuit will work but if you drive both transistors at the same time you will have a short-circuit in the mosfets so be careful.
Or use something like PocketMagic » A simple H-Bridge design with transistors

Alex
 
Last edited:

That's right alex,when ever H-bridge arrangement is used in a circute, the high side gate voltage is always higher than the low side gate voltage,and if you apply the same voltage to the gate, the high side will over heat and even burnt.
 

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