I am wanting to make a motor driver using a SN754410 Quadruple Half-H Driver IC.

The SN754410 requires external flyback diodes. Here is an example circuit:

enter image description here

My question is, how do I choose which diodes to use? Two popular choices seem to be the 1N5819 and the 1N4007, but I don't know why.

What factors are involved in choosing suitable flyback diodes?

I'll speculate:

  1. Cost
  2. Current rating (motor operating current, or higher?)
  3. Voltage rating (motor operating voltage, or higher?)
  4. Switching time (does this matter with flyback diodes?)

The H bridge chip you are using has 1 amp capability (2 A non-repetitive). If you are using it correctly i.e. within spec then the diode you need has only to be rated about 1 amp. A 1N4007 is rated at 1 amp continuous and 30A non-repetitive so on the face of it it fits the bill.

As for your choice of H bridge, there are far better choices (dependant on the voltage supply). See this.

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When choosing a diode for the configuration you described, you are primarily concearned by the severity of the voltage pulse you will get when you turn your inductive load OFF.

This is governed by the inductance of the motor, if there are already some snubbing circuits on it, the motor current, frequency of operation etc.

Generally speaking, you need a good enough I2t for the diode forward current and for some application you would also need fast switching diodes.

But in general almost any diode will do the job as long as it can carry enough current.

Can you tell us more about the application?

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  • \$\begingroup\$ Not only carry enough current, but have a high enough voltage rating for the given supply PLUS any regenerative energy that might come back as the motor decelerates. For lower voltages Schottkys have no reverse recovery, which is good. For higher voltages if the PWM frequency is high enough you would certainly want to consider fast or ultra-fast recovery diodes. \$\endgroup\$ – John D Jan 2 '15 at 20:43

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