Sunday, 8 September 2013

Reverse polarity protection (reverse protection) simulation and schematic.

This post will provide a tutorial of how to protect your circuit from reverse voltage (Reverse Polarity). In this post I will simulate it with details at every step to make you understand. You may download the Proteus simulation or schematic from the download section at the bottom of this page. Sometime we often put a battery inside an electronic equipment in a reverse polarity this causes it to burn. So as a good design engineer your circuit design should have a protection to maximum possible reasons that causes complete failure to your device operation. Your product should be reliable.

There are many possible ways to protect your circuit from reverse polarity. This is the simplest way to achieve protection as well as it requires least components. The benefit of using this technique is this makes your circuit working in any polarity. So you don’t need to worry about polarity just put battery in any configuration. But this circuit has one tradeoff which I will explain later in this post.

Proteus Simulation:

In the following figure 1. An animation shows how your circuit is protected against reverse polarity and also how it works in any configuration of battery. The red tracks represents positive tracks and blue tracks represents ground tracks. Whereas the arrows shows the direction of flow of current.

Figure 1. Proteus Simulation.

Detail description:

In the following figure 2. We have a small setup to simulate reverse protection circuit. We have two batteries BT1 and BT2 where BT2 is in reverse polarity. We have a DPDT switch which I used to simulate the reverse polarity. When I switch it up it will connect the battery BT1 to load and when I switch it down it will connect BT2 to load which is in reverse polarity. We have a bridge or you may use four diodes connected in bridge configuration. I labeled them as 1, 2, 3 and 4 for explaining simulation. And at the end we have a dummy load. Your circuit should be connected here. A voltmeter is connected in parallel with the load. I will explain the purpose of this later in this post. So using this circuit before your circuit design makes your circuit working of the polarity of connected battery.

Figure 2. Schematic for simulation.

In the following figure 3. We have a simulation picture. In this picture I first connected the battery in right polarity to the load as you can see the switch SW1 is up. And the current is flowing from the battery BT1. In this case as you can see the arrows shows the direction of current. The current goes from Diode 1 towards the load whereas diode 4 is in reverse biased. As current passes from the load it goes from the second diode 3 (Forward biased) where diode 2 is also reverse biased. Hence your circuit gets a positive current cycle when the battery polarity is right.

Figure 3. Battery BT1 Simulation.

Now the case in which battery is connected in reverse polarity (switch SW1 is down). The BT2 is connected to the load which is in reverse polarity as shown in following figure 4. This time the current flows from diode 2 (forward biased) whereas diode 3 is in reverse biased. This current after passing through the load passes through diode 4 (forward biased this time) towards the negative terminal of the battery whereas diode 1 is in reverse polarity. So in this way your circuit is protected and as well as works in any configuration of battery polarity. We can say that our circuit is independent from battery polarity.

Figure 4. Battery BT2 Simulation.


            The tradeoff of this circuit is, it adds two diodes in series with the load. This creating it to have a voltage drop of 1.4V on diodes and load always gets battery voltage – 1.4VDC on its terminals as you have seen on voltmeter. For 12VDC battery we have 10.6VDC at load. But this voltage drop can be down to 0.6VDC to 0.8VDC by using schottky diodes. In case of schokkty diodes we have battery voltage – 0.8VDC at terminals of load. Which is not bad, to protect a circuit. Or you may increase the input voltage to compensate this drop of voltage according to your application requirement.


You can download Code (Schematic and Proteus simulation). Click here

Reading Suggestions:
·         Over Voltage Protection
·         AC Voltmeter RMS + Peak voltage 

For all topics Click here:

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