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Dual Relay Driver: Boost Sensitivity with BC547 Circuit
Description
This straightforward and practical solution offers a seamless method for connecting two relays within your project. The relay driver leverages a standard BC547 NPN transistor (or an equivalent) to enhance the input impedance. This is a frequently utilized design. It is capable of controlling a diverse range of relays, including reed relays. Transistors Q1 and Q2 form a basic common-emitter amplifier, significantly amplifying the effective sensitivity of the 12-volt relay coil approximately 100 times. Consequently, the current gain for this circuit is 100. Employing this configuration minimizes the relay’s sensitivity to a few volts. Resistors R3 and R4 limit the input current flowing into transistors Q1 and Q2 to a safe level. Diodes D3 and D4 function as EMF dampers, suppressing any arcing that might occur when the relay de-energizes.
Picture of the project:
Circuit diagram:
Parts:
- R1-R2 = 1K
- R3-R4 = 5.6K
- C1-C2 = 100nF-63V
- D1-D2 = Red LED
- D3-D4 = 1N4001
- L1-L2 = 12V Relay
- Q1-Q2 = BC547
Specification:
- Input - 12 VDC @ 84 mA
- Output - two SPDT relay
- Relay specification - 5 A @ 230 VAC
- Trigger level-2~5VDC
- Berg pins for connecting power and trigger voltage
- LED on each channel indicates relay status
More about components
The BC547 integrated circuit, a fundamental NPN bipolar junction transistor, is employed in this circuit. This versatile component facilitates amplification of small electrical signals and is commonly utilized in switching and amplification applications. The BC547 is a general-purpose transistor featuring a moderate gain and low saturation voltage, making it suitable for a wide variety of low-power circuits. Its availability and relative ease of use contribute to its widespread adoption.