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Sawtooth wave generator Click here for the circuit diagram
Sawtooth wave generators using
opamp are very common. But the disadvantage is that it requires a bipolar power
A sawtooth wave generator can
be built using a simple 555 timer IC and a transistor as shown in the circuit
The working of the circuit can
be explained as follows:
The part of the circuit consisting of the capacitor
C, transistor,zener diode and the resistors form a constant current source to
charge the capacitor. Initially assume the capacitor is fully discharged. The
voltage across it is zero and hence the internal comparators inside the 555
connected to pin 2 causes the 555's output to go high and the internal transistor
of 555 shorting the capacitor C to ground opens and the capacitor starts charging
to the supply voltage. As it charges, when its voltage increases above 2/3rd
the supply voltage, the 555's output goes low, and shorts the C to ground, thus
discharging it. Again the 555's output goes high when the voltage across C decreases
below 1/3rd supply. Hence the capacitor charges and discharges between 2/3rd
and 1/3rd supply.
Note that the output is taken
across the capacitor. The 1N4001 diode makes the voltage across the capacitor
go to ground level (almost).
The frequency of the circuit is
f = (Vcc-2.7)/(R*C*Vpp)
Vcc= Supply voltage.
Peak to peak voltage of the output required.
Choose proper R,C,Vpp
and Vcc values to get the required 'f' value.
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