555 Timer Oscillator

  
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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 - schematic

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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