555 Timer Oscillator

Posted on Feb 6, 2014

As discussed in previous blog posts, pin 5 terminal is voltage control terminal and its function is to control the threshold and trigger levels. Normally, the control voltage is +2/3VCC because of the internal voltage divider. However, an external voltage can be applied to thisterminal directly or through a pot, as illustrated in figure, and by a

555 Timer Oscillator
Click here to download the full size of the above Circuit.

djusting the pot, control voltage can be varied. Voltage across the timing capacitor is depicted in figure, which varies between +Vcontrol and ½ Vcontrol. If control voltage is increased, the capacitor takes a longer to charge and discharge; the frequency, therefore, decreases. Thus the fre ­quency can be changed by changing the control volt ­age. Incidentally, the control voltage may be made available through a pot, or it may be output of a transistor circuit, op-amp, or some other device.

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