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Circuit diagram without relay protection

A circuit without relay protection uses solid-state components like transistors or op-amps to provide short-circuit or overload protection without mechanical relays.Overview

Circuits without relay protection replace electromechanical relays with fully electronic components to detect faults and control outputs. These designs are faster, more compact, and more reliable because they avoid mechanical wear and contact bounce. Common applications include bench power supplies, transformerless power supplies, and low-current electronic devices.

Key Components and Operation
  1. Transistor-Based Protection
    • Two transistors can be connected in an anti-parallel configuration to act as switches.
    • Under normal operation, one transistor conducts, allowing the green LED to indicate normal status.
    • During a short circuit, the conduction state switches, activating a red LED and buzzer to alert the user ( ).
  2. Op-Amp Comparator Circuits
    • An operational amplifier (op-amp) like the LM358 can be configured as a comparator.
    • A low-value series resistor senses the output current.
    • When the voltage drop across the resistor exceeds a threshold, the op-amp output changes state, signaling an overload or short circuit ( ).
    • This method allows precise electronic control without mechanical relays.
  3. Transformerless Power Supplies
    • Capacitive reactance is used to drop AC mains voltage without a transformer.
    • A high-voltage capacitor limits current, and a zener diode stabilizes the output voltage.
    • While this design does not include relay protection, it can be combined with transistor or op-amp circuits for electronic fault detection ( ).
Advantages
  • Faster response to faults compared to mechanical relays.
  • Compact and lightweight, suitable for small electronic devices.
  • No mechanical wear, increasing reliability and lifespan.
  • Visual and audible alerts can be integrated easily using LEDs and buzzers.
Example Applications
  • Bench power supplies with short-circuit detection.
  • Low-power transformerless DC supplies.
  • Electronic devices requiring overload or fault indication without bulky relays. By using transistors, op-amps, and resistive sensing, circuits can safely detect and respond to faults without relying on relays, making them ideal for modern compact electronics ( ).
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