Zener diode across servo rails on Pixhawk2/pixracer

It is recommended to add a zener diode ( IN5339) to condition the power across the servo rails in Pixhawk. Is it recommended for Pixhawk2 and pixracer also?

not sure why zener diode should be there, as a voltage limiter we need a serial resistor too, so … if a power supply for the servo rail push more voltage as expected, there will be something wrong with regulator, so … this Zener can’t help with power failure

the short answer is NO for Pixhawk 2,
On Pixhawk 2, the servo rail is NOT used as a power input source.

However, if you wish to connect the servo rail into the system as a backup power source. connect the servo rail power (5.6v max) to the power input 2 (NOT 1)

Power input 2 is fitted with the zener diode, and some more logic to protect the system.

@bluuu, the purpose of the zener is to protect the system from power spikes above 5.6v. Many servos, especially the digital ones, will have back emf over 11v, which due to the design of the system, would disqualify the servo rail as a power input source (Max 5.7v)

As these spikes are very low energy, and very short in duration, a simple zener is enough to clamp the voltage to 5.6, and therfore allow this to be used for the rest of the system.

so… regarding Pixracer, @pkocmoud may be able to answer you better, as it is his board, but I cannot see any harm in it, however, I am not aware of how or if the servo rail power ties into the system.

@proficnc, ok, you are right with strong servos, it makes sense

1 Like