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# Relay Fuse Schematic Circuit Diagram

#### Absence of Current Limiter in Basic Chargers and Power Supplies

Relay Fuse: Typically, basic battery chargers and power supplies lack a current limiter feature. However, in numerous scenarios, incorporating a safeguard against short-circuits would be beneficial. The diagram illustrates an electro-mechanical fuse designed to fulfill this function, presenting an add-on solution for improved safety. Two variations are available—one tailored for power supplies (a) and the other for battery chargers (b). The subsequent description focuses on the power supply version (a).

#### Electro-Mechanical Fuse Design for Power Supplies

The circuitry details a practical solution for enhancing safety in power supplies. The electro-mechanical fuse, outlined in the diagram, acts as a protective measure against short-circuits. The circuit’s functionality and components are elucidated in the following description, providing insights into its implementation for added safety in power supply units.

When power is switched on, the relay gets a short, energizing pulse of current via C1. Since the relay contacts then change over, the relay remains energized. When a short-circuit occurs at the output terminals of the power supply, the relay is deenergized, and the connection between input and output is broken. The relay is re-energized by a new pulse of current via C2 after the short-circuit has been removed and Si is pressed briefly. Capacitor C2 also prevents an overload if S1 is pressed while the short-circuit persists. The capacitor is discharged via R1 when S1 is opened. Diode D1 (biased via R2) shows when the circuit is off.

#### Battery Charger Circuit Variation: Power-On Relay Activation

In contrast to the previously described battery charger, a key distinction exists in the diagram. During power-on, the relay’s activation doesn’t rely on a capacitor but is initiated by the charging battery through D4. Should the battery reach a critically low state, rendering it incapable of providing sufficient current to trigger the relay, an alternative method involves energizing the relay briefly by pressing S2, utilizing the C3-R4 combination.

#### Adjusting Bias Resistor Values and Relay Voltage

The values assigned to bias resistors R2 and R3 hinge on the specific LED in use and the prevailing supply voltage. Additionally, it is imperative that the relay voltage align appropriately with the overall supply voltage for optimal functionality. Careful consideration of these parameters ensures the proper operation of the battery charger circuit.

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