Friday, January 22, 2010

Rangkaian Osilator Gelombang Sinus Variabel.

Osilator Gelombang Sinus Variabel (15 to 150kHz)

This is a circuit of sine wave oscillators covering a frequency range of 15 to 150kHz in four switched steps. Two conditions exist for a sinusoidal oscillator. Regenerative or positive feedback, and a closed loop gain of unity. The losses in the wien feedback circuit, are such that the open-loop gain of the amplifier must also exceed 3.

rangkaian osilator sinus variabelSkema rangkaian osilator sinus variabel

The circuit gain is provided by a FET type op-amp (LF351), but LF351 may be difficult to obtain, for a replacement you can use TL071CN or TL081CN. The Maplin order codes are RA67X and RA70M respectively. The wien network is a parallel combination of resistors and capacitors, in series with a series RC network. Regenerative feedback is applied from the op-amp output, to the serail RC input and continues. Stabilization is required to prevent the otherwise Uncontrolled oscillation from building up and becoming unstable.

There are two common methods of stabilizing a wien oscillator type. A thermistor with a NTC in the series leg of the feedback loop or an incandescent lamp (with a positive temperature coefficient) in the shunt leg of the feedback loop. The bulb used here is a 6V 60mA type Maplin code BT99H. A 12 Volt bulb rated 60mA or 40mA will also work. The feedback arrangement works as follows. As a bulb filament heats up its resistance increases. This will decrease the overall gain of the amplifier, as the output signal is fed back to the input.Similarly, if the output of the signal amplitude decreased Appearing at the bulb would be less, its filament resistance would drop and the gain would be increased. Therefore a stable output amplitude is produced. The 1k preset is adjusted for minimum distortion. Note that split supplies are used and a ganged 10k Potentiometer controls with a 10:1 frequency range.

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