protection


Using LM317 with Overvoltage Protection

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 […]


Logic PSU With Over-Voltage Protection

A simple 5 Volt regulated PSU featuring overvoltage protection. The 5 volt regulated power supply for TTL and 74LS series integrated circuits, has to be very precise and tolerant of voltage transients. These IC’s are easily damaged by short voltage spikes. A fuse will blow when its current rating is exceeded, but requires several hundred […]


Reverse Polarity Protector

A series diode is often used as a means of protecting equipment from accidental power supply reversal, particularly in battery-powered equipment. Due to forward voltage losses, this is sometimes impractical. One solution is to use an enhancement mode P-channel power Mosfet (Q1) in series with the positive supply rail. A device with low drain-source “on” […]


DMM Fuse Protector

Typically the input protection fuse of your DMM will blow in the middle of a demonstration or an exciting phase of your construction work. Spare fuses are always hard to find, and if available take a lot of time to install. This circuit replaces the fuse by a 500 mA current limiter. When resistor R1 […]


Overvoltage Protection

When a sensitive circuit must under no circumstances have too high a supply voltage applied, then some means of disconnecting the supply must be provided. One way to achieve this is to trigger a thyristor to blow a fuse. A less destructive alternative possibility is to use a MOSFET to disconnect the supply. An over-voltage […]


Short-Circuit Protection With A MOSFET

If you have an application in which a MOSFET is already used to switch a load, it is relatively easy to add short-circuit or overload protection. Here we make use of the internal resistance RDS, which produces a voltage drop that depends on the amount of current flowing through the MOSFET. The voltage across the […]



8V DC Power Supply With Over-Voltage Protection

This 8V DC power supply was designed for use with an expensive piece of electronic equipment. It features full over-voltage protection as a precaution against regulator failure, either in the supply itself or inside the equipment it is powering. The circuit uses a conventional full-wave rectifier, followed by a 3-terminal voltage regulator (REG1) with appropriate […]


8V DC Power Supply With Over-Voltage Protection

This 8V DC power supply was designed for use with an expensive piece of electronic equipment. It features full over-voltage protection as a precaution against regulator failure, either in the supply itself or inside the equipment it is powering. The circuit uses a conventional full-wave rectifier, followed by a 3-terminal voltage regulator (REG1) with appropriate […]


Short Circuit Protection For Balanced Supply Rails

This circuit was designed to protect a dual rail power supply from shorts across the two rails. It uses an optocoupler to monitor each supply rail, with the internal LEDs powered from ZD2 and ZD3 and the associated resistors. While the LEDs are on, the optocoupler’s internal transistors are both turned on which ensures that […]