Reversed DC Polarity Protector

The Idea of Reversed DC Polarity Protector came to me when a Cousin of mine burnt the main board of a DC powered TV. This happened when he wrongly connected (plugged) DC source plug into the TV’s DC input jack – socket. The fuse was overrated and could not blow up (on time) to break the circuit. This brought about an idea of this article.

Is it necessary for my project or device using DC supply? Is that your question? The fact is that, SOME of these devices or probably your projects are not reversed DC polarity protected. Also, the fuse might have been overrated. Therefore, even if you are building an electronic device or project as your hobby, you will need this in case of reversed power polarity. Except your device, project, or circuit automatically switches to adopt reversed DC supply, you need this reversed DC polarity protector. Otherwise, powering these devices with a reversed DC polarity especially powerful circuit causes damages to the circuit. Hence, there is necessity for a protective circuit like this.

It is a simple circuit which doesn’t need much effort to build. It also comprises of very few and cheap components to get it ready! Adding this simple circuit to your DC especially Battery or AC to DC adapter powered electronic design or device will help in terms of reversed polarity mistake.

Anyways, this article is important for every DC powered projects or circuits. This is because, it adds more protection to your precious electronic or project.

The components you will need

You will need these components to build this reversed DC polarity protector. They are cheap and easy to obtain which you may even find in your bin.

  • LEDs – 2
  • Dual Power Diode – 1
  • Fixed Resistors – 2
  • Push to reset button overload circuit breaker or fuse – 1
Reversed DC Polarity Protector Circuit 1


reversed dc polarity protector 1

Values of the components
  • LED1 = Red LED
  • LED2 = Green LED
  • R1 and R2 = 390 Ohms
  • D = MUR3040 Dual Diode. You can use two power diodes in parallel if you can’t get the dual power diode
  • CKT BKR = Push to reset button overload circuit breaker. The rating that is; Voltage (V) and current (A) of this circuit breaker depends on the power your device or project consumes. You can use a right rated fuse in place of the circuit breaker.
How the circuit above works

LED1 that is the red LED lits only if the polarity is reversed. The diode (D) senses a reversed polarity thereby acting in forward direction and the circuit becomes short circuit right from the diode’s point. This sends back high current to the circuit breaker or fuse. If the circuit breaker senses this current as overloaded current, it opens the circuit. Also, if it is a fuse, it blows off thereby, opening the circuit.

LED2 which is the green LED always lits only if the polarity is correctly connected. This indicates right polarity source from the input.

However, this circuit works perfectly for powerful projects or circuits especially those ones that are rated 12W and above. Meanwhile, below are the other types which can be used for low power projects.

Reversed DC Polarity Protector Circuit 2

reversed dc polarity protector 2

Values of the components
  • LED1 = Red LED
  • LED2 = Green LED
  • R1 and R2 = 390 Ohms
  • D = MUR3040 Dual Diode. You can use two power diodes in parallel if you can’t get the dual power diode

The second circuit above does not use circuit breaker or fuse. When the input DC is reversed, LED1 lits indicating that the supply polarity is reversed. Because the diode D in the circuit above is in forward bias connection, it blocks the supply from passing. Thus at this point, the LED2 does not lit. However, when the DC input is correctly applied, the LED1 goes OFF and because diode D is in forward bias now, it allows power to pass to the output. At this point, LED2 lits indicating correct polarity DC supply.

Reversed DC Polarity Protector Circuit 3

circuit 3


The circuit above uses bridge rectifiers diode. This circuit tolerate both forward DC supply or reversed supply. Anyhow the DC supply is applied, it corrects to forward form.

2 thoughts on “Reversed DC Polarity Protector”

  1. Ngenda mwangana

    This is a great invention, you really opened my mind and I will no longer have worries about reversed polarity
    Keep it up!

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