Electronic – DC motor driving

Yes, you can definitely parallel the two outputs of an L293D. I made a few stepper drivers based on L293D with parallel outputs and had no problems.

As this application note from ST Microelectronics (APPLICATIONS OF MONOLITHIC BRIDGE DRIVERS) states:

Higher output currents can be obtained by paralleling the outputs of both bridges. For example, the outputs of an L298N can be connected in parallel to make a single 3.5 A bridge. To ensure that the current is fairly divided between the bridges they must be connected as shown in figure 2. In other words, channel one should be paralleled with channel four and channel two paralleled with channel three. Apart from this rule the connection is very straightforward - the inputs, enables, outputs and emitters are simply connected together. The outputs of an L293 or L293E can also be paralleled - in this case too, channel 1 must be paralleled with channel 4 and channel 2 with channel 3.

But you should be aware that the total current capability of the parallel outputs would be less than the sum of the two channels (< 1200 mA).

EDIT: The only differences between the L293/L293E and the L293D are that:

• the L239D has internal clamp diodes included

• the L293/L293E has higher output current capabilities.

Maximum power dissipation of the L293D is far less than 5W. The N type package will warm up 67 degC per watt dissipated (pg 4 of data sheet) and 2.5W would likely push it past the limit of 150 degC stated on page 4 also.

It's hardly ever good news with the L293D (and its near-identical twin the SN754410). These are poor choices for H bridges if you are pushing the current over 0.5A and by the sound of it you are. There is also a suspicion that an RC motor probably isn't rated at 12V but somewhat less so you are probably pushing this just too far. Most RC batteries I've seen are about 7.5V.

Back to the L293D (aka SN754410).... When driving a load it doesn't act like a relay contact - it loses about 1.2V on the lower transistor and 1.4V on the upper transistor - take half an amp or so and the power dissipated is already 1.3 watts and has taken the N package device up 87.1 degC above ambient. That's quite hot in an ambient of 25.

Not a good choice of H bridge but, to be honest I'm yet to hear of an application when the L293D (SN754410) is a good choice. I'd look into the DRV8837 from TI. It has a combined high and low side mosfet on resistance of 0.28 ohms meaning, at 0.5 A the total volt drop is 0.14 volts and the internal power dissipated is 70mW. Maximum motor voltage is 11V but, I suspect you may be over-powering your motor anyway. There are probably others from TI that have a higher voltage rating.