What is Hysteresis in Electronic Circuits

You might have searched regarding what is hysteresis a number of times through many different posts on different websites, but to no avail.

You might have also tried to find a comprehensive as well as an easy explanation regarding the same through various websites.

However, the explanations provided over these websites are pretty long and difficult to grasp.

Let’s try to learn through a simple example, what exactly hysteresis in an electronic circuit means.

How Hysteresis Works

The behavior of a relay towards a continuously applied variable voltage can be used to explain hysteresis concisely. Let's learn it through the following experiment:

1. Take a 12 volt relay, connect a variable power supply to it and gradually increase the voltage from zero to 12.
2. You will find that the relay activates at about 11 volts. Logically, if now the voltage is reduced below this level, the relay should deactivate.
3. However, that does not happen. Practically it will be seen that the relay deactivates only after the voltage is reduced well below 9 volts.
4. This voltage lag between the activation and deactivation thresholds can be defined and understood as the hysteresis; in this case it is for the relay.

Similarly, all electronic circuits especially in single BJT circuit you will find this small disadvantage, which may pose difficulty in maintaining fixed thresholds levels.

In efficient electronic circuits the level of hysteresis is kept to the minimum. If you have more doubts regarding what is hysteresis, do feel free to respond with your comments.

Hysteresis in Opamp

On the contrary, opamps circuits tend to be very sharp and effectively avoid hysteresis while handling a specified operation.

You might have come across many opamp based battery charger circuits, wherein the absence of a hysteresis actually becomes a disadvantage and we have to force hysteresis by adding a feedback resistor across the output and one of the input pins of the opamp to enable the hysteresis effect.

Therefore hysteresis in electronic circuits can be sometimes beneficial and sometimes a disadvantage depending on the application specifications of the circuit.