Hybrid H bridge single relay configuration
November 12, 2010
So I have been brainstorming H-bridge designs for a 5V motor with 5A stall current. I want max speed from the motor off 4xAA batteries, so I am considering using a high side relay vs a high side transistor. I would like the H bridge to:
- Have minimal voltage loss, to get motor voltage as close to Vcc as possible
- Be small enough to hopefully fit on top of a small RC car chassis such that the body fits over it
- Handle currents up to at least 10A
- Be fairly inexpensive
- Be suitable for PWM
- Obviously prevent shoot through and overheating
I like the small Rds(on) value of the IRFZ44 and current capability. If a relay is used on the high side then at 5A the voltage loss should be less than 100mV. Relays tend to be bulky so I am thinking maybe I can get away with only using one. I've drawn out a couple of basic configurations using a single relay as the high side of a bridge.
The schematic with a SPDT relay has three control lines to be used with an AVR uC:
- Direction: selects which way the motor turns
- CW PWM: motor logic for clockwise direction
- CCW PWM: motor logic for counter clockwise direction
I don't know how safe this configuration is, as if the relay doesn't switch as expected then shoot through will occur.
The second schematic might be the solution to this, which uses a DPDT relay to disable shoot through. I am also considering using an AND MOSFET driver such as the TC4468 in this configuration.
Please feel free to point out any schematic design flaws, ideas for better configurations, or your thoughts on the pros and cons. I am just starting to come around to discrete H bridges since a single L298 is not cutting it.
Thanks in advance.