Inverters

Friday, May 2, 2008

Multivibrator

A-stable multivibrator(TR type)
I will introduce the a-stable multivibrator circuit which used two transistors.The a-stable multivibrator is the circuit which repeats the high level (H) condition and the low level (L) condition alternately.‚hIn case of the transistor type, the voltage (Vcc) of the power supply can be comparatively freely set compared with the IC type. Also, it is possible to assemble compactly compared with the IC type when considering the power circuit and so on, too.However, because VEB is a maximum of 5V in the case of a transistor called 2SC1815 used this time, as supply voltage, it's to 5V. For details, please look at circuit explanation.


Calculation of the blink periodfor A-stable multivibrator (TR type)
The period which repeats a blink is fixed by the value of capacitor (Cx) and resistor (Rx), and capacitor (Cy) and resistor (Ry). The half period time (t) is possible to calculate by the following formula. The half period is the time which is made H condition or an L condition.It uses a calculation formula on the side of TR1 as an example.t : second, Cx : Farad, Rx : ohmA repeat period is decided by the combination of Cx and Rx, and Cy and Ry.In case of Cx, Cy=47 µF, Rx, Ry=22 k-ohm, it is as follows.
The time that TR1 becomes OFF condition (t1)
t1= 0.69 * Cx * Rx= 0.69 * 47 * 10-6 * 22 * 103= 0.713 secondsTR2(t2) is similar. The frequency (f)
F= 1 / ( t1+t2 ) = 1 / ( 0.7 + 0.7 )= 0.71 Hz
The measurement frequency of the circuit which was made this time was to 0.78 Hz be.The error with the calculation value is for the error of the part and the characteristic of the transistor and so on. The measurement value of Cx, Cy was to approximately 47 µF be. The measurement value of Rx and Ry was to about 20 k-ohm be. When calculating with this value, the frequency becomes about 0.77 Hz. The calculation value and the measurement value are an near value.Don't expect a correct period with this circuit. The period changes with the temperature around. So, this circuit isn't possible to use for the circuit with strict period.

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