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PS Protector

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 Robot Power Products 

Power Supply Protection 


Scorpion Nano

The PS Protector family is a range of related products offered by Robot Power for the protection of AC/DC power supplies used to power motors and motor controllers.  The function of the PS Protector family of products is to protect this type of power supply from reverse current flow generated by electric motor Back-EMF.  Battery power supplies can generally just absorb a brief amount of reverse current without issues.


PS Protector Inline Medium

·       Voltage: 6V - 48V

·       Current: 20A-30A continuous, 60A peak

·       Size: 2.95" x 1.35" x .55"

·       Weight: 14g

·       Ideal diode function

·       Reverse current flow protection

·       Reverse input polarity protection

·       Inductive kickback spike protection

·       Optional plastic enclosure


PS Protector Inline Small

·       Voltage: 6V - 36V

·       Current 8A-12A continuous, 25A peak

·       1.8" x 1.3" x 0.5"

·       Weight: 8g

·       Ideal Diode function

·       Reverse current flow protection

·       Reverse input polarity protection

·       Inductive kickback spike protection

·       Mounts to ServoCity® Actobotics™ 1.50" pattern mounting system


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·       PS Protector Small drawing

·       PS Protector Medium drawing

·       PS Protector Inline Hookup Guide

·       PS Protector Medium enclosure drawing

How it works

Due to the nature of electric motors, a rotating motor generates a voltage of reverse polarity to that applied by the driving motor controller. If this "Back-EMF" voltage is higher than that applied to the motor by the motor controller it can cause a reverse current flow from the motor to the power supply.  The most common scenario for this to occur is when the motor is operating near full speed and the motor controller rapidly commands a lower power level.  At full speed the motor is generating Back-EMF nearly equal to the power supply voltage less losses such as the load and friction.

When a sudden lower voltage is applied to the rotating motor by the motor controller the driving voltage seen by the motor is reduced before the mechanical motor rotation can catch up.  This leaves the motor generating the Back-EMF of its current rotation speed while the driving voltage from the motor controller is at a lower level.  This causes current to flow from the higher voltage potential generated by the motor to the lower applied by the motor controller i.e. back from the motor into the motor controller and hence back into the power supply.

Due to the nature of the output regulation circuits in the vast majority of AC/DC power supplies, attempted reverse current flow causes the power supply to increase its output voltage to maintain current flow out of the power supply.  The resulting voltage spike may be large enough to exceed the maximum ratings of voltage sensitive circuits such as the power supply output regulation circuit or the motor controller circuits.  This can lead to the destruction of the power supply or the motor controller or both.

The PS Protector family acts as an "Ideal Diode" by using a low-resistance MOSFET to pass current in the forward direction with very low losses but to instantly (a few nanoseconds) switch off the MOSFET to block reverse current.  As soon as the output voltage level is lower than its input the PS Protector turns the MOSFET on to allow normal current flow again.

A second function of the PS Protector family is to allow multiple power supplies or battery supplies to power a load or for multiple loads to use one power supply without interfering with each other.  Scenarios such as hot swapping batteries or power supplies or seamless failover are also supported by the PS Protector.

Scorpion Nano


Robot Power offers the PS Protector products fully assembled and ready to use. Check the Web store to purchase them.

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