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555 Voltage-controlled Oscillator with an Adjustable Duty Cy

2015-01-30 01:38  
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555 Voltage-controlled Oscillator with an Adjustable Duty Cycle Period
The voltage-controlled oscillation circuit has been shown in picture3-19. 555, R1, R2, C1~C3 and VT1 constitute a voltage-controlled multi-vibrator. As a voltage-controlled resistance, JFET can change the impedance between D/S. The coupling capacitance of D and S is used to eliminate the effect of other direct voltage on JFET. Timing capacitance of C1 and C2 should be selected as large as 10 times of C3. Advantage of this circuit is that, an adjustable and changeable resistance can be formed by changing VGS, so as to obtain a large duty cycle and a changeable period.