555 Timer Oscillator
A voltage-controlled oscillator (VCO) using the timer 555 is shown in figure.
The circuit is sometimes called a voltage-to-frequency converter because the output frequency can be changed by changing the input voltage.
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 this terminal directly or through a
pot, as illustrated in figure, and by adjusting 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 frequency
can be changed by changing the control voltage. 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.
Thank you
1 comment:
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