Therefore, the oscillation frequency depends on the value of R 1, R 2, R 3, and C 1. Similarly, the threshold voltage is higher the charging time is slower. Suppose the threshold voltage is lower, the charging time is faster. Because these resistors will decide the threshold voltage of the capacitor, and the capacitor will charge up to this voltage level. Similarly, a smaller value of R 1 and C 1 causes higher frequency oscillation.īut, in the calculation of frequency, resistor R 2 and R 3 also play a vital role. And for a long time of charging and discharging, we need to set a more significant R 1 and C 1. Therefore, for lower frequency oscillation, we need a longer time for charging and discharging the capacitor. In the Op-Amp relaxation oscillator, the R 1 and C 1 contribute to the frequency of oscillation. Frequency of Op-Amp Relaxation Oscillator In the RC circuit, the charging and discharging time decides by the time constant. The frequency of the Relaxation Oscillator depends on the charging and discharging time of the capacitor. UJT Relaxation Oscillator Waveform Relaxation Oscillator Frequency The voltage waveform across the capacitor and resistor R 2 is shown in the figure below. And the voltage appears across the resistor R 2 during discharging of the capacitor and remains zero during charging of the capacitor. Hence, the process of charging and discharging the capacitor generates a saw-tooth waveform across the capacitor. After that, the UJT turned OFF and started the capacitor charging. The capacitor continues to discharge until the capacitor voltage reaches the valley voltage (V V) of UJT. Then the capacitor stops charging and starts discharging through the resistor R 1. When the voltage across the capacitor is greater than the supplied voltage, it enables the UJT turned ON. The capacitor continues to charge until it reaches the maximum supplied voltage V BB. And the capacitor starts charging through the resistor R by the equation below. We assume that initially the capacitor is discharged. The emitter terminal of UJT is connected with a resistor and a capacitor.
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