Security & SafteySensors - Tranducers Circuits

Slave Mains On-Off Control Schematic Circuit Diagram

Synchronizing Mains-Powered Equipment: Control Purpose and Applications

This control system is designed to synchronize the activation and deactivation of mains-powered equipment in harmony with a master control unit. Its practical application is notably valuable in audio racks, where signal sources such as cassette decks, CD players, tape recorders, tuners, and the like are coordinated to power on and off alongside the power amplifier, ensuring seamless operation.

Current Monitoring and Optoisolator Integration: Efficient Sensitivity Control

The circuit effectively supervises the master unit’s current consumption through the optoisolator IC1, utilizing relay K2 for this purpose. By adjusting P1 to maximum sensitivity, corresponding to the highest resistance value, a mere few milliamperes prove adequate for triggering the activation of connected slave units through K3. It’s crucial, however, to exercise caution with the maximum sensitivity setting, reserving its use for exceptional cases. This caution is necessary to accommodate potential leakage and quiescent currents in the master unit, ensuring the control system’s reliability.

Slave mains on-off control Schematic diagram

Master Unit Control Logic: Triggering Load Activation

When the current draw of the master unit surpasses the predetermined trigger level, the transistor within IC1 initiates conduction, causing the output of IC2 to shift low. Consequently, T1 conducts, activating the load (the slave) through relay Rel. Following the master unit’s shutdown, capacitor C2 undergoes charging via R5. Once C2 reaches a specific voltage threshold, the comparator toggles, subsequently deactivating the slave through Ti and Re after approximately 500 ms.

Visual Indicators and Load Capacities: Status LEDs and Maximum Loads

The control’s operational status is visually indicated by two LEDs: D5 serves as the on/off indicator for the control mechanism, while D6 displays the on/off state of the slave unit. Notably, the master and slave outputs can handle maximum loads of 500 W and 750 W, respectively.

Safe Construction and Earth Track Strengthening: PCB Design Considerations

To ensure optimal performance and safety, constructing the control circuit on the provided PCB (depicted in Fig. 2) is highly recommended. Key connections are established through three 3-way PCB terminal blocks. For enhanced safety measures, reinforcing the earth track on the board is crucial. This reinforcement is achieved by incorporating a copper wire with a cross-sectional area of 2.5 mm² or larger, enhancing the board’s grounding reliability.


Slave mains on-off control Schematic diagram
WARNING. Since the board carries dangerous voltages at a number of points, it is essential that proper electrical insulation be applied. Never work on the board when the mains are connected to it. Make sure that no part can be touched when it is being adjusted or used

Parts list

  • R1 = 120 Ω
  • R2, R5, R11 = 10 kΩ
  • R3, R10 = 1 kΩ
  • R4=33 Ω
  • R6= 68 Ω
  • R7 = 270 kΩ
  • R8, R9 = 47 kΩ
  • R12 = 2.2 kΩ
  • R13 = 220 Ω. 1 W
  • C1 = 470 μF, 25 V
  • C2 = 47 μF, 25 V
  • C3 = 150 nF, 630 V
  • C4 = 10 μF, 25 V
  • D1-D4 = 1N5408
  • D5 = LED, red
  • D6 = LED, green
  • D7 = 1N4148
  • B1 = 840C1500
  • T1 = BC327

Slave mains on-off control Schematic diagram

Slave mains on-off control Schematic diagram

Slave mains on-off control Schematic diagram

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