Created on 2010-07-20 17:39:00

Question:

Is it recommended to use a flyback diode to protect the APx Aux Control Out when driving a relay?

Answer:

It is common practice to put a reverse connected diode or alternative suppression circuit across the coil of a relay, to protect the driving circuit from the high voltage spike emitted when the relay is turned off. However, you can generally use the Aux Control Out on the APX to drive relays without needing an external flyback diode. The auxiliary outputs are driven with a TI TPIC6273 relay driver, which has built-in voltage clamps on the outputs for inductive transient protection. Also there’s a 10k pullup to +5 V (and 100pF/25V to ground).