What are the common types of linear power supply overvoltage protection?
The power supply may malfunction in multiple ways, and a particularly concerning possibility is that the series adjustment components of the linear power supply (i.e., the main transfer transistor or FET) may experience a short circuit.
If this situation occurs, a very large voltage, commonly known as overvoltage, may appear on the circuit being powered, causing catastrophic damage to the entire device.
By adding additional protective circuits in the form of overvoltage protection during the electronic circuit design phase, this unlikely but catastrophic possibility can be prevented.
Most power supplies designed for highly reliable operation of high-value devices incorporate some form of overvoltage protection in their electronic circuit design to ensure that any power failure does not cause damage to the power supply equipment. This applies to both linear power supplies and switch mode power supplies.
Some power supplies may not have overvoltage protection and should not be used to power expensive devices - some electronic circuit design can be done to develop a small overvoltage protection circuit and add it as an additional item.
Basic knowledge of overvoltage protection
There are many ways of power failure. However, to gain a better understanding of overvoltage protection and electronic circuit design issues, it is easy to give a simple example of a linear regulator using a very simple Zener diode and series transfer transistor.
Although more complex power supplies can provide better performance, they also rely on series transistors to deliver output current. The main difference lies in the way the voltage regulator is applied to the base of the transistor.
Usually, the input voltage causes the voltage across the series regulator components to drop by several volts. This enables the series transfer transistor to fully regulate the output voltage.
Usually, the voltage drop across series transmission transistors is relatively high - for a 12 volt power supply, the input may be 18 volts higher to provide the required regulation and ripple suppression.
This means that there may be a significant amount of heat dissipation in the regulator components, coupled with any transient spikes that may occur at the input, which means there is always a possibility of failure.
