This is a motor driver board that can drive 2 DC motors in Forward or Reverse with full speed control (using an external PWM signal). It can handle at least 25 amps per channel continuously at 24vdc. I designed it using a basic H-bridge with 4 switches, 1 switch going to positive (+) and 1 switch going to negative (-) for each motor terminal. By switching 2 of the switches simultaneously (1 positive and 1 negative), you can change the polarity that is going to the motor which will in turn switch the direction.
This board uses Mosfets for the switches because of their high-speed and low-loss capability and their ease of use. I used P-channel mosfets for the high-side (positive) switches and N-channel mosfets for the low-side (negative) switches. With mosfets, you can use 1 and operate it at it's rated current (in this case 50amps) or you can put multiple mosfets with their like-terminals tied together and multiply the amount of current the total circuit can handle, also allowing for more heat to be dissipated. So instead of using only the 4 mosfets needed to complete an H-bridge, I used 3 mosfets per leg of the H-bridge (3 mosfets per leg x 4 legs = 12 mosfets per H-bridge). Also, this board is a dual H-bridge, meaning there are 2 complete H-bridges, so it has 24 mosfets total on the board.
I etched the board using 2oz. copper clad from digikey. I used resistor networks instead of single resistors for each of the mosfets (they are the yellow things that look like mini-school busses below the mosfets). All the files you might want to see to make one yourself are included here. You will need Eagle Cad to print the files.
FQP47P06 P-channel Mosfet - Digikey - $1.73 ea. (x 12)
FQP50N06-L Logic level N-channel Mosfet - Digikey - $0.99 (x12)
47 ohm SIP-6 bussed resistor network - Digikey - $0.50 (x8)
2n7000 N-channel logic level Mosfet - Digikey - $0.45 (x4)
10k 1/8watt pull-up/down resistors - Digikey - $1.50 for 50pk (you only need 24)
2-position 5.04mm spacing terminal blocks - Radio Shack or Digikey - $2 for 2pk (x6 or (3) 2-packs)
80mm 12v PC fan - Newegg - $2
various bolts and nuts 8mm
1 sided copper-clad 3"x5" 2oz.
Steps to build:
Step 2: Open the .brd file and print only the bottom layer. Use the "black" and "solid" options if not already selected.
Step 3: Prepare the copper clad by scrubbing it with a Scotch brite pad and cleaning it very throroughly with Acetone and paper towels (clean with acetone several times).
Step 3: Turn your iron on HIGH.
Step 4: Place the print face down on the copper clad board and place iron on top. Apply pressure and heat for about 3 minutes, moving every 30 seconds.
Step 5: Let copper board sit for a few minutes before placing it in a bowl of warm soapy water for 30 minutes.
Step 6: Rub the paper off with your thumb until there is only black toner traces left.
Step 7: Mix an etchant solution using 2 parts Hydrogen Peroxide with 1 part Muriatic Acid. BE CAREFUL and wear gloves and safety goggles. This will take about 10 minutes.
Step 8: Drill all holes (preferrably with a drill press).
Step 9: Place components and solder. Solder Mosfets last.
Here are some pics: