Trouble with NMIH-0050 H-Bridge

[DSandberg]

Hello,

I am using a NMIH 0050 to power a electronic dog door. I'm using a Basic Stamp 2 to drive it.

When the motor is running in clockwise, the yellow error LED flickers constantly. The motor runs slower than in the counter clockwise direction. The error light does not illuminate in the counter clockwise direction once it has reached full speed.

Also I use PWM to start the motor to take slack out of the gears and cables. During this power up stage, the error LED is on constantly in both directions.

I've checked current draw and it's 2.6 amps in the CW direction and 2.4 in the CCW direction.

Voltage is constant at 10.3 volts.

I've checked for short circuits at the motor circuit and can find none.

Any suggestions would be helpful.

Thank you for your help.

Daryl

[Dave]

Hey Daryl,

It sounds like the h-bridge is going into overcurrent shutdown, but just barely. You state you're measuring 2.4 amps one direction, and 2.6 the other way, but perhaps this is only filtered "meter" reading. If measuring on a scope, there might be substanitially higher current spikes seen. What is the stall current of this motor? The description makes it seem like the protection of the chip is further slowing the motor, to get away from any current spikes, then because it was only a minor spike switching back on again after the PWM signal changes. If the current jumps to over 6 Amps, then drops to nothing in shutdown, it could be showing that average of 2.4 to 2.6 A.

[RMDumse]

The same thing might be happening with voltage shut down. I've seen an average reading over 6V, but the yellow light flickering on when the load would draw down below 5.3V. You couldn't see the drop on a meter, but a scope showed the rail wasn't strong enough to hold the motor up above cutout underload.

[DSandberg]

It turns out my power supply just didn't have enough horsepower to get the job done. I was using three 1.2 amp transformers in parallel to drive the motor. Not enough. The voltage would drop enough for the h-bridge to kick out.

Thank you for your help.