Astable Multivibrator with 2 Transistors

Posted on Nov 10, 2012

This circuit is basically simple and easy to build, it uses two transistors as active components and a few passive components like resistors, capacitors and two LEDs. The circuit makes use of the MPS2222 transistor. You can use any NPN type transistor as the basis of your circuit provided that, the transistors Emitter-Base Voltage is less than 12V and has a maximum value of 5V.

Astable Multivibrator with 2 Transistors - image 1
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This is to ensure that the circuit will work under a 9V Battery power supply. The circuit generates a H(HIGH) to L(LOW) level and L to H level transition. This H to L or L to H transition is generated by capacitors C1 and C2 and resistors R1 and R2, the LEDs acts as output loads to the circuit and the other resistors serves as current limiting resistors for the protection of the LED diodes. Taking one-half of the circuit we can calculate the time period which makes the high or low transitions for a single transistor. Thus, the time constant can be calculated as: t = 0.693 RC The transition frequency from HIGH to LOW state can be computed as:

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