Ok,
Looks like for this application, (simple mobile robot vehicle), I can use the H-bridge I designed a while back, I am now using a 9volt battery for the logics unit, and 2 AA batteries for the H-bridge drive voltage, the motor I'm using is a small 5volt, hacked servo motor.

I have built and run extensive tests on this and I am satisfied that this will work for THIS application.

The reason for extrememly high resistanace is to not load the battery so much.

First here is the data I gathered during the test run.



Here is the original schematic
the motor is run off of 2 AA batteries, and the logic is run off of 9 volt battery.



here is the unit breadboarded for one motor only.



Here is the dynamic test applying a squarewave signal to the unit.
I had to use a resistive dummy load so as to check the switching ability of circuit.

100 hZ.



200 Hz.



and 400 Hz.



This unit will only be switching during sensor inputs (no need for fast switching), such as bumper switches and infra-red obststacle avoidance, most of the time the motor will be in continuous run mode.

After an hour the mosfets were still cool to the touch.


Thanks everyoe for the info on my last thread I appreciate the time you took to exoplain things.

 

A real marvel, hobbyist! What, may I ask, is the signifance of having those diodes at the bases of your transistors?

 

A real marvel, hobbyist! What, may I ask, is the signifance of having those diodes at the bases of your transistors?

They are used to keep the bases isolated from each other, otherwise problems could arise as current through the bases interact with each other.

As well as kepping base currents away from the sensor circuits, this way the sensor circuits will have the full drive, and not interact with the base currents.

 

I am afraid you may have a problem turning on the upper two MOSFET transistors. The problem is that the gate on these two FETs has to go 5 to 10 volts higher than the source. Since your gate driver for these two devices can not go more positive than the positive supply, you will not be able to turn these devices on.

There are available high-side drivers made for the express purpose of driving these gates to voltage greater than the positive supply just for this purpose.

An alternative would be to use P-channel Mosfets in the two upper switching devices. You will need to change the gate driver circuit to accommodate the p-channel mosfets.

hgmjr

 

I am afraid you may have a problem turning on the upper two MOSFET transistors. The problem is that the gate on these two FETs has to go 5 to 10 volts higher than the source. Since your gate driver for these two devices can not go more positive than the positive supply, you will not be able to turn these devices on.

There are available high-side drivers made for the express purpose of driving these gates to voltage greater than the positive supply just for this purpose.

An alternative would be to use P-channel Mosfets in the two upper switching devices. You will need to change the gate driver circuit to accommodate the p-channel mosfets.

hgmjr

Sorry my fault on the schematic. I used the old drawing with the old supplies.

My new drawing should have 3 volts, for the motor, and 9 volts for the logic circuits.

 

The old IRF610 is for high voltage and low current. But your requirements are the opposite.
If its gate is at +9V then it might not supply any current to the motor since its gate-source turn on voltage is 10V. For its source voltage to the motor to be +3V then its gate voltage must be +13V.

 

This is the 2 H-Bridges been built into PC Boards. So far.



after loading.


closeup both PC boards.




size reference using a 9 volt battery.


The 5 headers at the bottom row are for
sensor inputs.

1. side bumper switch.
2. fromt bumper switch.
3. Infra-Red detector.
4. Aux. 1
5. Aux. 2.