555 timer ic

PC Power Saver Schematic Circuit Diagram

Minimizing PC Power Consumption: 555 Timer and Relay Circuit

This circuit is meticulously designed to reduce the quiescent power consumption of PCs and notebooks, employing the trusty 555 timer and a relay as its core components. During operation (when the connected PC is powered on), the circuit itself dissipates around 0.5 W. Remarkably, when switched off (with the relay de-energized), the total power draw reduces to zero, ensuring optimal energy efficiency. To employ this circuit, a PC or notebook with a USB or PS/2 keyboard socket is essential; this socket must only receive power when the PC is active.

The power saver unit can effectively control PCs or even entire multi-way extension blocks. Conveniently, the unit can be housed within a standard AC power adaptor (with an earth pin), as demonstrated in the author’s prototype photograph. The PC is plugged into the output socket of the power saver, with an additional connection established between the unit’s control input and a PS/2 (keyboard or mouse) socket or USB port. Only the 5 V supply line of the interface is utilized. Pressing button S1 on the power saver activates the unit, triggering the monostable circuit formed by the 555 timer through the network composed of R4 and C7.

PC Power Saver Schematic Circuit Diagram

Relay Activation and PC Power Management

Upon activation, the relay RE1 is engaged, closing its contacts. During this period, the PC receives tentative power through the relay, regulated by the duration set by P1 (approximately 5 s to 10 s). If the PC fails to provide the necessary 5 V signal from its USB or PS/2 connector within this interval, indicating it is powered on, the monostable timer will expire. Consequently, the relay will deactivate, cutting power to any connected device. No further current will be drawn from the supply, and the PC cannot be turned on without pressing the button on the power saver beforehand. However, if the PC delivers 5 V to optocoupler IC2 within the given timeframe, indicating it’s switched on, the monostable remains triggered. The relay stays energized until the PC is powered down and the 5 V supply vanishes from its USB or PS/2 interface.

Automatic Power Disconnect: Seamless Shutdown Process

After the monostable timer lapses, the relay deactivates, disconnecting the power saver from the AC source. There’s no need to manually switch off other components; shutting down the system suffices, and the power saver will handle the rest. Even during software updates or when the system is in idle mode, the power saver operates efficiently after the PC shuts down.

Safe Power Supply and Component Protection

Power for the unit is secured through a basic supply circuit utilizing a miniature transformer. Alternatively, a 12 V AC power adapter can be used, provided a relay with a 12 V coil voltage is employed for RE1. Careful consideration should be given to components’ ratings. If necessary, P1’s adjustment range can be extended by using a larger capacitor at C6. The relay requires at least two normally open (or changeover) contacts rated at a minimum of 8 A. S1 must be rated for 230 VAC (or 120 VAC in the US) operation. Proper isolation and safety precautions are vital; components connected to the mains voltage must be well-insulated. Special attention is needed to maintain a minimum 6 mm gap between components associated with the PC and those connected to the AC line potential, ensuring safe operation.

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