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Overvoltage Protection(LM317)

2016-09-11 12:52  
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This article describes the Overvoltage Protection (LM317). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: LM317.

The circuit diagram shows the over voltage protection as a feature of LM317 linear voltage regulator.

Over voltages come from several source or factors which are usually in the form of transients. Transients are represented in spikes which are short and fast disturbance or change in the voltage and current component.

It only occurs in circuits containing conductance and capacitance. The causes are typically from power outages, short circuits, tripped circuit breakers, lightning spikes, inductive spikes and other malfunctions from power company.

Figure:1 Circuit Diagram

Figure 1 Circuit Diagram

As an example using a 12V battery source, the LM317 voltage regulator can be used to obtain 6 Volts. To protect any device from over voltage, there are ways such as adding relays or a zener diode. A relay switch functions by opening or closing under the command of another circuit. But finding a relay that would limit the output from 6 V to 12 V is not easy.

Fortunately, zener diodes are more abundant. A 6.2V zener diode rating can be used to surpass any excessive voltage set by the voltage regulator, to prevent more damage to the circuit. The components will be as follows:

ZD1 – 6.2 Volts
R1 – 1K ohms
R2 – 1K ohms
T1 –NPNTransistor (low power)
T2 –NPNTransistor (acts as a switch)

Every circuit design needs to be tested carefully as to avoid further damage to the equipment that will be connected. The trial can be done by using a multimeter, and gradually increasing the circuit voltage. Once the circuit turns off the supplied voltage, take note of the reading which will signify the threshold voltage of the zener diode.



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