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tilden h-bridge with current sense, input protection needed?


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Hello,

 

I have to control a small DC motor with no limit switches on the end positions, so I have to stop it when I detect a current surge.

It's a 12V motor, when running it uses about 15-20mA, and when stalled it goes to 300mA.

Since I don't have an h-bridge available but I have lots of transistors, for such a small motor I though I could use a tilden h-bridge, adding a small resistor on the low side and connect it to an analog input on the msp430.

I simulated the circuit on circuitlab (OK, a resistor is not a motor but I thought that in a pinch it would do) and I see that with a 5 Ohm resistor I see 112mV with the motor running (600 Ohm resistor) and ~900mV with the motor stalled (40 Ohm). I even tried with a 0 Ohm resistor and I see no more than 976mV, so well below the limit, but I'm not sure the simulation is right.

Do you think it should be safe or should I add some more protection? How?

TIA

 

Edit: on circuitlab I used 2N3904/2N3906 because that's what they have, I'm going to use BC327/BC337, I think it shouldn't make a big difference, am I right?

 

Edit2: here's a copy of the circuit, in case you don't want to go to circuitlab:

540x405

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