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Sine wave oscillator low frequency-constant amplitude

2015-01-01 00:00  
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In the Sine wave oscillator circuit often to be use the thermistor and Incandescent lamp,
for upset the output of circuit has fixed value,
the resistance of the thermistor dependent on temperature and as a result to voltage drop across of it.

From the slow response of the thermistor make to properties of temperature against resistance is not linear like with that do not distortion value in this oscillator circuit.

In this circuit, we use a zener diode in performs this function instead by is used to limit a voltage. Then, the bridge circuit consisting of R1, R2 and C1, C2 are defined the frequency of the generator. And, the active devices in the circuit, Q1, Q2 will need to has a gain ratio nearly three times so will be completed produce the frequency.

When the output is reached to the maximum value. The ZD1 will start to conduct current and reduce the rate increase of the amplifier section come down, with this damping, The sine wave signal has likely to decrease. to prevent ZD1 limited to the output signal too early, then to add the resistor R5 series with ZD1 and all parallel with R4.
when the voltage drops across the ZD1 to threshold level, the impedance of this network will be gradually reduced to the sine wave is stable very great. Although there is limiting the sine wave positive phase, but the peak negative signal, it is limited to by automatic.
The VR1 should be adjusted carefully, to avoid having to trim the output signal. Half-wave portion negative of output signal will be very linear, But a half-wave positive is distortion slightly, because it be limited.


However is not in applications because some job do not to need the completion of the sine wave such as : the vibrato of the instrument.
The output voltage of this sine wave oscillator circuit can adjust by the potentiometer VR2 during 0 to 4 Vp-p

The section frequency is given by the formula:
f = (1/2) 3.14 R1 C1
(R1=R2 ; C1 = C2)

from value is set in the circuit will have the frequency 6Hz, and If use the value in parentheses will has frequency about 0.01 Hz. The R1 and R2 should be several hundred kilo-ohm. If the value is too low to cause the load to the amplifier at low frequencies. The portion negative of the output signal may has been trimmed, Causing the distortion. Elements the DCV of the output will be filtered out by connection the capacitor electrolytic high value the serial output..

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