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LAMP BURNING WHEN PHONE CALLS MOC3020 BT137 Schematic Circuit Diagram

Upon connecting the illustrated circuit to the telephone line, the lamp illuminates upon receiving an incoming call. The circuit is divided into two parts, each isolated from the other through the MOC3020 optocoupler. This optocoupler is a component that enables the control of high voltages and currents using low voltages without direct electrical connections. The initial circuit, located in the lower segment, is linked to the telephone line.

Let me explain the components and their functions in this circuit:

1. MOC3020 Optocoupler:

The MOC3020 is an optocoupler, also known as an opto-isolator. It consists of an LED (Light Emitting Diode) and a phototransistor inside a single package. Optocouplers are used to transfer electrical signals between two isolated circuits by using light waves to transmit the signal. In this case, it allows the low voltage circuit connected to the phone line to control a high voltage circuit without direct electrical connection.

2. BT137 Triac:

The BT137 is a type of semiconductor device known as a triac. A triac is similar to a transistor but is capable of conducting in both directions when triggered. It is commonly used for switching AC loads. In this circuit, the triac is used to control the lamp based on the signal received from the optocoupler.

3. Lamp:

The lamp is the output device in this circuit. When the MOC3020 is triggered by the phone line, it activates the triac, allowing current to flow through the lamp and illuminate it.

Working Principle:

When there is an incoming call, the voltage on the phone line triggers the LED inside the MOC3020 optocoupler. The light emitted by the LED activates the phototransistor, which in turn triggers the gate of the BT137 triac. Once the triac is triggered, it allows current to flow through the lamp, lighting it up.

During any incoming call on the telephone line, the voltage reaches an AC value of 75V. This voltage passes through components R1 and C1 before entering a bridge diode composed of 4 1N4007 diodes. Afterward, it is rectified and regulated into a direct current by the circuit. In every phone call, this section is stabilized at 33V by the DZ1 signal, ensuring protection for the optocoupler.

The second part of the circuit is the upper segment, controlled by the local power network. This portion comprises R1, R2, C4, TRC1, BT137 triac, and a 220V lamp. Upon receiving a phone call, the gate end of the BT137 is triggered via the photo triac of the optocoupler, causing the lamp to illuminate. This illumination continues until the power supply is disconnected from the mains.

MOC3020 Pinout BT137 Pinout

An optocoupler (also called optoisolator) is a semiconductor device that allows an electrical signal to be transmitted between two isolated circuits.
Optocouplers can either be used on their own as a switching device or used with other electronic devices to provide isolation between low and high-voltage circuits. You’ll typically find these devices being used for Microprocessor input/output switching. DC and AC power control.
The MOC301XM and MOC302XM series are optically isolated triac driver devices. These devices contain a GaAs infrared emitting diode and a light-activated silicon bilateral switch, which functions like a triac. They are designed for interfacing between electronic controls and power triacs to control resistive and inductive loads for 115 VAC operations.

Note:

  • The specific values of resistors, capacitors, and other components in the circuit, as well as the connection details, would depend on the exact requirements and the characteristics of the components used.
  • It’s crucial to ensure proper isolation and safety measures, especially when working with components connected to the phone line, to prevent damage to the equipment and ensure user safety.

Please keep in mind that working with high voltages can be dangerous. If you’re not experienced with working on such circuits, it’s advisable to seek assistance from someone with expertise in electronics.

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