LC multivibrator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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Figure 1 shows a diagram of the generator. When the power is turned on through the resistor R1, the capacitor C3 begins to charge, as the voltage on C3 increases, the logic elements go into an unstable state, an oscillatory process begins, the frequency of which is determined by the parameters of the series circuits C1L1 and C2L2.
In steady state, at C1=C2 and L1=L2, the voltage at C3 corresponds to half the supply voltage, and there is a meander at the outputs DD1.1 and DD1.2. If the parameters of the frequency-setting elements change, then the duty cycle of the signal will also change. The inputs of the elements DD1.1 and DD1.2 contain protective diodes that shunt the LC circuit, so it is recommended to connect the inputs DD1.1 and DD1.2 to the LC circuits through resistors with a resistance of 10K ... 100K.
Ris.1
The duty cycle of the signal can be converted into voltage; for this, integrators are connected to the generator through buffers DD1.3 and DD1.4 (Fig. 2). Such a circuit can be used to measure the parameters of capacitors or inductors. The change in voltage at the output of the op-amp will be proportional to the change in parameters C or L.
Ris.2
This generator was used as a small displacement meter, while the frequency-setting circuits had the following parameters С1=С2=680pf, coils L1 and L2 were wound on frames with a diameter of 8 mm with ferrite trimmers, and contained 40 turns of PEL-0.3 wire, the trimmer of one from coils, freely moving in the frame, operating frequency - about 1 MHz, supply voltage 12V. If you move both trimmers, you get a differential sensor.
Ris.3
A varicap can be connected to the output of the operational amplifier (Fig. 3), included in one of the LC circuits so that negative feedback would form - a circuit with automatic adjustment will be obtained, the mismatch signal is removed from the output of the op-amp.
Author: Dr.Mabuzu; Publication: N. Bolshakov, rf.atnn.ru
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