Transistor h-bridge VS driver IC chip (L293D)

Mar 7, 2009
Category:Arduino Electronics 

As mentioned in an earlier post, I suggested the motor driver IC would be preferable over four transistors and lots of wire due to it's small and neat package! However I have just realised something that may sway me in the other direction...

I was running my Arduino on battery, trying to prototype a simple vehicle, and after being distracted for some time came back to find a very flat battery, even though none of the motors were doing anything.

After recharging the battery, the first thing I did was grab my multimeter and measure how much current my circuit was drawing whilst in its idle state. It came in at about 45mA, and considering my battery only has a capacity of 170mAh, this gives an idle battery life of about 3.5 hours.

To reduce this current drain slightly, I found that by disabling the h-bridge that I was not using, by pulling the enable pin low, I could save on 15mA. As this is a dual h-bridge, if I disabled the other one I could save on another 15mA, but as this was the one I was using I had to wire that enable pin to an output of the Arduino, so it could enable it as and when it needed it.

This got the overall quiescent current down to about 15mA, which gives a much better battery life of about 11 hours, however I wondered how this would compare to my transistor h-bridge.

So for a quick test I rebuilt my transistor h-bridge, and measured the current drawn whilst it was doing nothing, and it barely registered, good enough to call 0mA.

So for battery-powered applications, the transistors may be preferable. I have looked at a couple of other motor driver chips, and they all seem to use a small quiescent supply current, one I saw used about half that of this chip.