![]() ![]() This circuit does not require a resistor-R. Therefore, we will have voltage across the relay coil about 12V-0.7V = 11.3V, etc. Which has value about 0.7 volts.įor example input from the pulse output digital pulse of 12 volts to drive to the transistor. By has various resistor-R limit proper current for circuit.įigure 3 is the driver relay circuit by use input voltage to feed to the relay coil but has some voltage junction base and emitter lead of transistor. ![]() Table 1 shows size of input voltage of various digital ICs and the relay coil need. Then, Look at Table: 1 The table input voltage, output current ICs, coil current, and limiting current resistor. For example, 2N3053, 2N2222 transistor, etc. There are a lot of transistors that have the hFE gain is more than 50. It is enough to the needs of the relay coil. So, get current out of the output is about 100 mA (2×50 = 100). Suppose the transistor has a currents Gain (hFE) about 50 times. In the circuit above, Here is how you can choose a proper number. VBE is a voltage across at base-emitter of a transistor. Vin = 5V, VBE of a silicon transistor is about 0.7V, Iin = 2 mA For example, input voltage of 5V, Current of 2 mA approximately. You can calculate a limiting resistors-R from the input voltage and current. And, the input current at output of a normal digital circuit is about 2 mA. The coil of relay needs a current about 100 mA. In the circuit below is most transistor relay driver circuit. So you need a helper, use a transistor to switch high current to drive the coil instead. To control relay to works.īut the most, its output is low current. Using the output pulse from a microcontroller or digital gate ICs. Sometimes you may use the relay with a digital circuit. To connect the voltage-V2 provides a high current (I2) to Load as we need. It makes the contact of relay connect together as a switch is closed. Thus, when the current flows through the coil. ![]()
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