ESD Protection and Reverse polarity protection

Introduction

Quite often, when we develop our PCBs, we only care about the circuit components that are essential for our projects, such as microcontrollers, LDOs, battery managers, LEDs, sensors, etc. Forgetting about the protection circuits which are very important to ensure the correct functioning of our project. Especially if we are using expensive components in our project.

But what do we need to protect our circuits from?

Answering this question is not easy because it depends on the project you are carrying out. In this post, we will see how to protect our circuits from two specific events that could compromise your PCBs. I'm talking about ESD(Electrostatic Discharge) and Reverse Polarity.

ESD Protection

The problem of electrostatic discharges is much underestimated by novices. It is very important to have a good knowledge of ESD as it helps prevent damage to our PCBs.

So how to prevent ESD problems?

Here's what you need to do:

• When designing your PCBs, insert components that protect your circuit from ESD. It is usually a good idea to add ESD protection to the input of a USB connector or other connectors that must be protected by the ESD. So for example you can use TVS Diodes to protect against ESD.
• During PCB assembly and testing, it is good practice to use anti-ESD bracelets to handle the PCB and components in total safety.

ESD protection positioned between USB-C and serial bridge:

A TVS diode therefore as soon as it is crossed by an excessive current diverts it to the ground.

So for the next project that you will carry out pay close attention to the problems that ESD can cause, and be concerned about preventing these malfunctions that could compromise the hours spent working on that project and also the economic impact it can have.

Reverse polarity protection

Now let's look at another problem that can damage our PCBs. Let's talk about reverse polarity. As the same word says, if we reverse the polarity of the power supply what happens to our circuit? What is the maximum voltage value that our circuit can withstand?

So, reverse polarity protection is an internal circuit that ensures that the device is not damaged if the power supply polarity is reversed. To prevent reverse polarity problems different components can be used, for example (add a simple diode or a Zener diode). The reverse polarity protection circuit cuts off power to the sensitive electronic circuits.

Example of Reverse polarity circuits:

• Schottky: Simplest but higher loss. Limited to low current.
• PFET is inferior that NFETs and costs more. Need external circuit(Zener clamp and resistors).
• Smart diodes: simplicity combined with the superior performance of NFET.

Obviously, the choice of the type of protection circuit to use depends a lot on the project. So the choice remains up to you when designing the PCB.

ESD protection and reverse polarity protection in one circuit.

It is possible to solve the problem of ESD and polarity inversion with a simple and practical circuit that you can use for your projects. Obviously, this solution that I propose to you is not suitable for all projects. It also leaves the choice of components to you to decide the maximum input voltage and other important variables that affect the effectiveness of the protection circuit.

Conclusion

Using ESD and reverse polarity protection circuits ensures greater reliability in your projects. I hope this post has been useful for you to develop your projects. If you have any questions, don't hesitate to ask.