# Help! H-bridge

Discussion in 'The Projects Forum' started by ericyeoh, Jul 11, 2010.

1. ### ericyeoh Thread Starter Active Member

Aug 2, 2009
58
0
Hai, If i wanna design a H-bridge with the supply voltage of 80V by using the diagram below, can the circuit withstand?
If the controller signal is only 5V, TR1=TR3=TP147(darlington PNP), TR2=TR4=TP142(darlington NPN), N1=N2=2n2222N, P1=P2=2N2907

i know the duty circle and the switching speed for mosfet would be better compare to the BJT however our experiment is only required to use BJT and not going for MOSFET.

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2. ### windoze killa AAC Fanatic!

Feb 23, 2006
605
24
I can't see any reason why it wouldn't work. The cct you show has a rail of +12V, if you want to use 80V then you will have to look at the resistors to ensure you don't over drive the transistors. You will also need to consider the current draw of the motor. Without checking the datasheets I believe the TIP darlingtons will handle the voltages. Just have to check the current.

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3. ### hgmjr Moderator

Jan 28, 2005
9,030
214
The only concern I would have is that the two PNP transistors TR1 and TR3 may not turn off very fast when you need them to. This could be improved by putting base-return resistors on them. Each base would have a resistor from it to the +power rail. That way when you turn them off, there would be a resistor to pull current out of the base.

hgmjr

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4. ### hgmjr Moderator

Jan 28, 2005
9,030
214
I just took a glance at the 2N2222 data sheet and noticed that it has a maximum Vceo of 30 volts. You will need to find you a transistor that withstand Vceo somewhere in the 90 to 100 volt if you intend to operate the motor at 80 volts.

hgmjr

5. ### SgtWookie Expert

Jul 17, 2007
22,182
1,728
You might use 43k base return resistors to get under 2mA current, and then you can use 1/4W rated resistors.

MJD112/MJD117 complementary transistors are rated for 100v with a 2A max collector current, but are rather overkill.

MPSA42 or MPSA43 would work for the NPN, MPSA92 or MPSA93 would work for the PNP, as long as you didn't sink much current from those voltages. These MPSAxx are all in TO-92 packages.

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