I saw previous postings about h-bridges, but they didn't seem to really help my problem. I am building a robot with a team of other students at school. As of right now, what the theoretical operation was supposed to be that when the remote control circuit wished to turn a motor on, the receiver would output a logical 1 +5VDC on that particular channel output. My job was to take that +5VDC and switch on 12VDC to that particular DC motor. After someone's recommendation, I went with the NDP6060L. It is a mosfet that can take a +5V TTL signal at the gate input and switch on +V from the drain through to the source at upwards of 48A.

My problem obviously has to deal with polarity. I attempted to hook up 4 of these mosfets together to form an H-bridge. I tied the gates between high-left and low-right, as well as tied the gates between high-right and low-left. In theory, I thought that when 1 channel went high, the current went from the drain to the source of the first FET, then go through the load (motor), after that it would go through the drain & source of the second FET to ground.

The motor does actually spin in either direction with this setup, however, instead of the motor pulling .6A like it normally does, it only pulls .1A

If need be, I could put some schematics of what I was trying to do, in case I'm not making any sense at all.

any input would be helpful. I'm trying to keep the size of the circuit down, while still being able to switch the 10A+ that I need for this rather heavy robot.

Thank you for your help.

 

Are you using an H-bridge driver? A FET turns on when the gate is so many volts above the source - 5 in your case. The high side FET has significant voltage on the source, though, and so the gate has to be maintained above the source voltage. A drive chip uses a charge pump to keep the gate voltage properly above that of the source.

 

i i'm not mistaken, there is this h-bridge driver in an ic. maybe you can google that.

 

I think beenthere has hit on the explanation to your problem.

It would be helpful if you would post your schematic so that we can take a closer look at what other issues you may have with your circuit.

hgmjr

 

there is this h-bridge driver in an ic

HIP4081A, MAX620 and IR2111 are some common ones.