Photo Optical Modulator: Photo Optical Modulator – The principle of an optical dc chopper is illustrated in Fig. 14.42. Devices of this type have been used widely in infrared signal detectors, whose output is a slowly varying dc product. The properties of the parallel connected photo resistor are such that the device produces a decrease …
Solid State Modulator/Demodulator Circuit: A solid state modulator/demodulator circuit is shown in Fig. 14.41. The transformer T is driven by an ac source and couples each secondary connected to the two transistor pairs, Q1 – Q2 and Q3 – Q4. During the first half cycle, point X is positive with respect to point Y. This …
Synchronous Vibrator and Synchronous Chopper: Low dc current may be transformed into a high voltage dc by simple chopper action. Although an inductive type transformation process is required, the output dc may be obtained without rectifying devices. Figure 14.39 shows a circuit function of a synchronous vibrator. Contacts a and b connect the input dc …
Varactor Diode Symbol: A specially processed junction diode that assumes the properties of a variable capacitor (about 5 – 250 pf) when its dc reverse voltage is varied is called a Varactor Diode shown in Fig. 14.37. This unique behavior can be used in special modulator circuits designed to turn a low voltage dc signal …
Transistor Chopper Circuit: Transistor Chopper Circuit – A single transistor used as a dynamic switch to convert low level dc signal to an ac waveform is shown in Fig. 14.34. If the voltage applied to the transistor base is negative (in the case of a PNP transistor), both emitter and collector diodes are shorted, and …
Diode Bridge Type Modulator with Transformer Coupling: Diode Bridge Type Modulator – Figure 14.33 shows a silicon diode ring modulator with an associated ac coupled dc amplifier. The amplifier itself has a gain of 65 db and a flat response within ± 1 db, from 8 Hz to 80 kHz. Precautions are taken to safeguard …
Diode Bridge Type Modulator with Transformer Coupling Read More »
Magnetic Modulator: The most reliable substitutes for electromechanical choppers are magnetic modulators. These devices reach a null stability as low as 10 μV, but their response time is often less than 2 Hz and the ambient temperature range is restricted. The 3-leg saturable reactor, shown in Fig. 14.32 falls within the category of magnetic modulator …
Self Oscillating Converter (Transistorized Chopper Circuit): Self Oscillating Converter (Transistorized Chopper Circuit) – A Transistorized dc to ac converter suitable for low level dc signal is illustrated in Fig. 14.30. The unique property of this assembly is that it starts to oscillate vigorously at very low levels of dc collector voltages at only a few …
Self Oscillating Converter (Transistorized Chopper Circuit) Read More »
What is Electromechanical Chopper?: Electromechanical Chopper – An ac amplifier must see ac in order to perform useful work. A fair number of chopping and modulation techniques are available to change direct current, or to change very slowly varying signals into square waves (or pulses). Associated circuitry, inserted at the amplification system common output, may …
Chopper Type DC Amplifier: A simple ac amplifier Transformer may be used to amplify a dc input through the use of additional circuit component known as chopper. In this circuit, the dc signal is first converted into an ac signal, amplified by a standard amplifier, and finally converted back to a dc signal. The chopper …