How to see the relay circuit diagram

The design and type of Relay switch circuits are very large, but many small electronic projects use transistors and mosfets as their main switching devices, because the Transistor can provide fast DC switching (ON-OFF) control of the relay coil from various input sources. So this is a small part of some of the more commonly used relay switching methods.

(NPN Darlington relay switch circuit/Transistor relay drive circuit/photocoupler drive relay circuit)

The design and type of relay switch circuits are very large, but many small electronic projects use transistors and MOSFETs as their main switching devices, because the transistor can provide fast DC switching (ON-OFF) control of the relay coil from various input sources. So this is a small part of some of the more commonly used relay switching methods.

1. NPN Darlington relay switch circuit

How to see the relay circuit diagram

Two NPN transistors are connected as shown, so that the emitter current of the first transistor TR1 becomes the base current of the second transistor TR2. Applying a positive base current to TR1 will automatically turn on the switching transistor TR2.

If two separate transistors are configured as a Darlington switch pair, a small Resistor (100 to 1,000Ω) is usually placed between the base and emitter of the main switching transistor TR2 to ensure that it is completely turned off. Similarly, use a freewheeling diode to protect TR2 from the back electromotive force generated when the relay coil is de-energized.

2. Transistor relay drive circuit

How to see the relay circuit diagram

When transistors are used to drive relays, NPN transistors are recommended. The specific circuit is as follows:

When the input is high, the transistor T1 is saturated and turned on, the relay coil is energized, and the contact is closed.

When the low level is input, the transistor T1 is cut off, the relay coil is de-energized, and the contact is disconnected.

The role of each component in the circuit: the transistor T1 is a control switch; the resistor R1 mainly acts as a current limiter to reduce the power consumption of the transistor T1; the resistor R2 makes the transistor T1 reliably cut off; the diode D1 reverses the freewheeling, and the transistor turns from on to off When it is off, it provides a bleeder path for the relay coil and clamps its voltage to +12V.

3. Optocoupler drive relay circuit

How to see the relay circuit diagram

As shown in the figure: 1U1-1 pin can be connected to 12V or 5V, 1U1 is on, 1Q1 is on, 1Q1-3=0V, and the voltage across the coil is 11.7V.

Pin 1U1-1 is not connected or grounded, 1U1 is blocked, 1Q1 is cut off, 1Q1-3=11.9V, and the voltage across the coil is 0V.

(NPN Darlington relay switch circuit/transistor relay drive circuit/photocoupler drive relay circuit)

The design and type of relay switch circuits are very large, but many small electronic projects use transistors and MOSFETs as their main switching devices, because the transistor can provide fast DC switching (ON-OFF) control of the relay coil from various input sources. So this is a small part of some of the more commonly used relay switching methods.

1. NPN Darlington relay switch circuit

How to see the relay circuit diagram

Two NPN transistors are connected as shown, so that the emitter current of the first transistor TR1 becomes the base current of the second transistor TR2. Applying a positive base current to TR1 will automatically turn on the switching transistor TR2.

If two separate transistors are configured as a Darlington switch pair, a small resistor (100 to 1,000Ω) is usually placed between the base and emitter of the main switching transistor TR2 to ensure that it is completely turned off. Similarly, use a freewheeling diode to protect TR2 from the back electromotive force generated when the relay coil is de-energized.

2. Transistor relay drive circuit

How to see the relay circuit diagram

When transistors are used to drive relays, NPN transistors are recommended. The specific circuit is as follows:

When the input is high, the transistor T1 is saturated and turned on, the relay coil is energized, and the contact is closed.

When the low level is input, the transistor T1 is cut off, the relay coil is de-energized, and the contact is disconnected.

The role of each component in the circuit: the transistor T1 is a control switch; the resistor R1 mainly acts as a current limiter to reduce the power consumption of the transistor T1; the resistor R2 makes the transistor T1 reliably cut off; the diode D1 reverses the freewheeling, and the transistor turns from on to off When it is off, it provides a bleeder path for the relay coil and clamps its voltage to +12V.

3. Optocoupler drive relay circuit

How to see the relay circuit diagram

As shown in the figure: 1U1-1 pin can be connected to 12V or 5V, 1U1 is on, 1Q1 is on, 1Q1-3=0V, and the voltage across the coil is 11.7V.

1U1-1 pin is not connected or grounded, 1U1 is blocked, 1Q1 is cut off, 1Q1-3=11.9V, and the voltage across the coil is 0V.