Transforming/translating circuit of some switching bipolar transistors to MOSFETs

Thread Starter

abdulbadii

Joined Aug 30, 2017
84
How do we transform/translate circuit in which configuration of the bipolar transistors as switching used, to MOSFET ones?

Such 12-24 V max 4 A load/motor in either of the BJT type H bridge circuit:
enter image description here
 

crutschow

Joined Mar 14, 2008
32,899
You would use the left circuit with P-MOSFETs on the top and N-MOSFETs on the bottom.
Using all N-MOSFETs, as the right circuit would require, would not sufficiently turn on the top transistors.

Note that, for the left circuit, add 1kΩ pullup resistors from each gate connection to V+.
You will need protection circuitry for the gate voltages to keep their Vgs below about 15V for typical MOSFETs (see data sheet), if the total V+ and V- voltages total more than 15V.
This can be as simple as some added voltage divider resistors at the gate to source of each transistor.
 

sarahMCML

Joined May 11, 2019
269
How do we transform/translate circuit in which configuration of the bipolar transistors as switching used, to MOSFET ones?

Such 12-24 V max 4 A load/motor in either of the BJT type H bridge circuit:
enter image description here
Incidentally, neither of these circuits will work, since in both cases the base of a lower transistor is connected to the base of an opposite side upper transistor. In the left circuit this clamps the base of the lower transistor to V+ - 0.7V, and for the right circuit its upper transistor's base to +0.7V.
 

Thread Starter

abdulbadii

Joined Aug 30, 2017
84
You would use the left circuit with P-MOSFETs on the top and N-MOSFETs on the bottom.
Using all N-MOSFETs, as the right circuit would require, would not sufficiently turn on the top transistors.

Note that, for the left circuit, add 1kΩ pullup resistors from each gate connection to V+.
You will need protection circuitry for the gate voltages to keep their Vgs below about 15V for typical MOSFETs (see data sheet), if the total V+ and V- voltages total more than 15V.
This can be as simple as some added voltage divider resistors at the gate to source of each transistor.
Is this correcting ?
Screenshot-2023-04-05-15-03-39.jpg
 

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sarahMCML

Joined May 11, 2019
269
No, I'm afraid not.
Although the new lower left NPN base, and therefore its emitter can now be pulled high, this does nothing to allow the lower left PNP transistor's emitter to be pulled low. Remove BOTH the "R_Small_US" resistors and place a separate one in each NPN base, up to the switch. Try 2K2 ohms. You don't need any for the upper transistors!
You should also have a resistor between the base and emitter of each transistor. Try about 220 ohms for the PNP's, and 1K for the smaller NPN's. These are to ensure that they turn off properly.
Please do number every transistor, it make referring to parts of the circuit so much easier!

The other circuit with opposite polarity transistors will be just the same, but in reverse.
 
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