Over Voltage Protection In LED Power Supply

1. What is over voltage protection(OVP)?

Over-Voltage Protect (OVP) circuits are mainly used at the input terminals that require rated voltage power supplies to prevent circuit system components or associated accidents caused by excessive input voltage!

Any electronic component has a maximum rated working voltage that it can withstand. Once the maximum withstand voltage range is exceeded, it is likely to be damaged. This is roughly the same as the consequences of excessive pressure on a person.

For example, if the voltage across the aluminum electrolytic capacitor exceeds the rated value, there may be a risk of explosion, as shown in the figure below: (from VISHAY Aluminum Electrolytic Capacitor 038 RSU data sheet)

2. What are the forms of over voltage protection circuits？

There are many specific forms of over voltage protection circuits, such as using comparators, ADCs, special chips, etc., which are nothing more than the idea of sampling, comparing, and controlling the input voltage. These are not explained too much. We only discuss voltage regulation. Application of diodes in over voltage protection circuits.

First, let’s take the simplest one, which is a Zener diode and a blowing fuse, as shown in the figure below:

When the voltage is too high, causing reverse breakdown of the Zener diode, it forms a low-resistance loop with fuse F1, and the current rises sharply and blows the fuse.

It should be noted that the zener diode D1 should be selected with a higher power, otherwise when the current rises, instead of burning out the fuse, it will explode. Dangerous actions, please operate under the guidance of professionals.

The following introduces an overvoltage protection circuit commonly used in actual work, as shown in the figure below:

Assume that the upper voltage limit of the protection is 24V (select the Zener diode D1 corresponding to the voltage regulation value). When the input voltage Ui is lower than 24V, the Zener diode D1 does not break down and is in a cut-off state. Therefore, the base of the transistor Q1 passes through the resistor. R1 and R2 are pulled up to the power supply Ui. The transistor Q1 is in a cut-off state because the base-emitter is at the same potential. The field-effect transistor Q2 is turned on because the resistors R3 and R4 divide the input voltage Ui to meet the gate-source turn-on voltage VGS. As shown below:

When the input voltage Ui is greater than 24V, the zener diode D1 is reversely broken down and the cathode is stabilized at 24V. Once the base-to-emitter voltage of the transistor Q1 is greater than the threshold voltage, it begins to conduct, which is equivalent to turning the field effect tube on. The gate G and the source S are short-circuited, which in turn causes the field effect transistor Q2 to be cut off, and the output voltage Uo is not output, as shown in the following figure:

Some engineers also connect a voltage stabilizing diode D2 in reverse parallel to the base-emitter of transistor Q1, in order to limit the base-emitter voltage of transistor Q1 beyond the limit value, and its voltage stabilization value is lower than what the three-pole sweet B-E junction can withstand. Voltage range, as shown in the figure below:

Do you think this Zener diode D2 can play a protective role?

3. OVP Application examples

Over voltage protection(OVP) circuits are widely used in various electronic equipment, such as power supply circuits, motor drive circuits, automotive electronics, aerospace electronics, etc.

Here are some specific application examples:

Over voltage protection on LED lighting

In led power supply circuits, over voltage protection circuits can protect the load at the output end of the power supply from over voltage damage.

For example: a government street lighting project bidding requirement requires that the power supply requires over voltage protection(OVP) of 265V and under voltage protection(UVP) of 90V. Then when the voltage exceeds 265V or falls below 90V, the power supply will cut off power to the street light and stop output. Beon has a driving power supply with this design.

The picture below is the test report of our engineering department. It can be clearly seen that the results of various parameters of the 7033-50W power supply under different voltage tests: Power (W), In Current (A), PF, THD, Output Voltage, Out Current (A), Efficiency, Ripple current, No-load V & No-load P.

If you also need OVP design LED driver, welcome to contact us. Our R&D team have enough experiences to support it.