دارات التحكم الإلكترونية .. كتاب التلفزيون الملون والعادي

17-19 Electronic Control Circuits:

Figure (19-25) shows the typical circuit for ultrasonic control circuits in the receiver. The input signal comes from the amplifier and is given instantaneously to a number of tuned circuits. The figure shows only two circuits. The bases of the transistors are grounded in the file L1 and L2, and there is no base bias in DC, and when the transistor is not forward biased, it is in the cut-off state, so all transistors on this line are naturally in the cut-off state. So if we assume that a signal at the entrance has a frequency of (37) kHz. The resonant circuit in the base of 02, tuned at this frequency, responds and passes the signal to the base of the transistor. When the signal goes in the positive direction, the base is forward biased and the transistor becomes conductive. The output of the transistor is a series of pulses smoothed by the capacitor C and the relay coil. The relay works and closes its contacts, which completes the motor circuit or the step switch circuit.

Electronic remote control circuit system:

The Quasar type remote control system, which we will explain here, is a solid state system - and the only electromechanical elements are the on and off relay for the current source, the relay and the channel selector motor, and the transmitted part in this type is shown in the figure shown previously - either In a television set, the electrical signal coming from the transmitter is fed to a three-stage preamplifier, and the preamplifier feeds the stimulus of the overall signals shown in Figure
(19-26) The overall signal waveform, in turn, drives the output stage and the channel selector coil discriminator. The output stage has a tuned input amplifier that accepts signals with a frequency range between (355 - 44.5 kHz) - and above this range, the response is broadband. As for the so-called function discriminator, its function is only to respond to a specific frequency, and reject any other frequencies. Thus, it distinguishes the appropriate frequency, so it is highly sensitive to this frequency only and neglects other frequencies.

His work in Function dis_criminators:

The output circuit feeds the function discriminator, and the word discriminator has no association or similarity with the discriminant used in FM modulation detection. But as mentioned above, it is limited. Acceptance of a certain frequency and rejection of other frequencies.

The function discriminator consists of three pairs of coils and two binaries. Each controller has its own files. These six files form the sequential loads for the output assembly of the control functions. Figure (19-26) shows a distinctive circuit to control the sound and the on and off with the diodes installed for the memory board and we will explain it later, and each of these six files has a frequency bandwidth between 500 to 1000 Hz, and this is what makes the file as an actual short circuit except when the frequency of the incoming signal It is the resonant frequency of this file, and at the resonant frequency, the file shows a maximum AC voltage, and this current is carried out in one of the diodes.

​In the previous scheme, if an amplified signal with a frequency of (38.5 kHz) is fed to coil 1 L, it will pass, because this high specification coil is tuned at a resonant frequency of 44.5 kHz, and a maximum voltage is generated on L2, which is tuned to
​​​​​​(38.5 kHz). The AC voltage coming from L2 is half-wave. Thus, the positive voltage appears on the dual-installation of the memory board. The work of this system after this circuit depends on the work of three memory boards, for sound - lighting and colors.

Memory Modules: The diagram (19-27) shows a simplified circuit of a memory board consisting of a neon bottle, a low leakage capacitor, and a MOSFET transistor.

Since the input impedance of the (Mosfet) transistor is very high and is of the order of (110) ohms. Neon is not connected in the bottle until the voltage on both ends reaches the ionization potential. The two elements appear as an open circuit. When the memory capacitor is charged - and remains so for a long period of more than 1000 hours. The charged capacitor fixes the voltage on the gate of the transistor (MOSFET), and so the current of the bank and the source remains constant. As for the efforts used for control purposes in the later stages, they are taken from a resistance value of (10,000 ohms).

The charging current of the capacitor passes through the neon bottle. The voltage applied to the neon is fixed to the diodes that are located outside the board - if the function signal exceeds (100 volts), then the voltage of the stabilization diode is 100 volts DC connected and the applied voltage is determined to (+ 100 volts DC) and since the ionization voltage of the bottle is (80 volts) approximately, the remaining voltage It is (20) volts used to charge the memory capacitor, and the stabilized voltage (80 volts) works in the same way, except that the current passes in the opposite direction, and the negative stabilization is lower than the positive stabilization, so the MOSFET gate voltage will not exceed the cut-off voltage.