This is a double H-bridge that can be used with PWM to control the output current. It uses some NAND logic to make sure there will be no shoot-through shortening the supply voltage by opening both high-side and low-side MOSFET’s at the same time.
I started out this design actually using an extra voltage source (battery) for driving the high side MOSFET’s. Then R24, R25 R26 and R27 had 9V extra voltage than the MOSFETS.
I didn’t like that solution, and just removed the battery. And the design still worked. A drawback with poorly driven high-side FET’s is that the will produce some heat. About 6W with 12V supply. The second drawback is that the voltage across the motor will drop by 3V. So if you have 12V power supply, the motor only get about 9V.
My intension for this H-bridge was to use it for an 50V driver for bipolar stepper motor. And if you supply 50V, the motor will get 47V. So who cares if there is some heat generated. It’s easyer to put on a heat sink, than creating an extra powersupply feeding the upper FET’s. The current would anyhow be limited by the PWM.
I did use this with an Arduino, and it worked well. It’s not that great with stepper motors, because you can’t use chop to boost the performance without risking to burn the motor.
The design of the NAND-gates are described in a previous article: How to design a circuit from NAND-gates only,using a truth-table
The diodes would be better to change to some fast schottky ones for better performance.
I’ve used the IRLU120N’s for small-signal as well, because they are cheap and logic level. They are rated at 100V 10A, but only 48W. So the current will be limited at higher voltages. You also need som bigger heat sink at higher voltages.
I have only tested this design for 20V and about 1.5A
I used FreePCB to create the PCB layout:
1200 DPI PCB-files can be downloaded from the link in the bottom of this article.
The finished board:
The heat sink MUST be isolated from the FET’s, so you have to use some isolating heat transferring film, between the FET’s and the heat sink. Shown in the picture below.
The finished board with heat sink: