دارة التنظيم الترانزستورية .. كتاب التلفزيون الملون والعادي

7-12 Transistor regulation circuit:

The zener diode regulation circuit is simple and easy, but it highlights the following defects:
1 - A large loss of power through the series and diode resistance

2- The voltage at both ends of the zener changes with a change in its current strength by a weak percentage

3- The output current is limited.

4- The zener diode circuit does not provide any filtering for large current zigzags, and these defects can be avoided by the transistor regulation circuit.
Figure (A-11-12) shows the box diagram of the transistor regulation circuit and the complete diagram of it in Figure (B-11-12).

Circuit working principle:

The regulation circuit includes a series transistor that protects the circuit from overcurrent and protects the load in the event of a short circuit in transistor Q.

The transistor Q2 is the error amplifier - the Zener diode CR provides the constant reference voltage for the circuit, and the two resistors R - R3 make it possible to adjust the output voltage, by changing its resistance that changes in Q2.

The transistor: adjusts and stabilizes the constant output voltage - by changing the voltage between the collector and the emitter (VCE). These changes add or subtract from the input voltage (7) as required to keep the output voltage 75. Changes in VCE are caused by a change in the emitter base voltage of the transistor: (VBE). .

The output voltage tends to rise when the continuous input voltage (V) DC increases or when the load current decreases or the load resistance (RL) decreases, and in both cases the voltage of 70 will rise, which is the (base) - emitter (VBE2) voltage of transistor 2 and increases Collector current Q2 via: R. This causes a decrease in the voltage between the base and the emitter (VBE) of the transistor, and in turn it decreases the current of the emitter - the collector of it - and this increases the voltage drop of the (VCE) and the output voltage is within its nominal value - and the output voltage tends to decrease due to a decrease in the input voltage 7 or due to an increase in The load current or the decrease in the value of the load resistance (RL) and here it will decrease to 70, i.e. (VBE2). The output current passing through Q2 and the resistor R due to the increase in voltage (VBE1) will in turn increase through the series pass transistor: this will reduce the voltage drop across the VCE (Q), and the output voltage 5 will increase to its nominal value.

And when the load current passes through: Q1 - this transistor must dissipate a significant amount of energy - so Q1 must be installed on a heat radiator.

circuit protection:

This circuit has two types of protection:

1- Protection from the dangers of short circuiting Q1 on the load


2- Protect transistor Q1 from malfunctioning if the load current is exceeded.

When one of the two cases occurs, the transistor 23 exhibits greater resistance - and this is what reduces the voltage of the output current except for the correct and safe value. It is noted that the capacitor does not work except when one of the two previous cases occurs - and in the normal case, Q is in the state of saturation due to the resistance RS, and so on, the resistance of the emitter - the collector practically = zero. This makes 03 unaffected by the circuit regulation in the normal case. When a short circuit occurs in the serial Q, the output voltage 75 and the load current (IL) will rise, so the current in R6 as well as the voltage on both ends will rise. In the normal state, the diode It does not conduct, due to its reverse voltage barrier. and he About (0.7 volts) However, increasing the current through R6 due to a short circuit will increase the voltage across R6 enough to break through the voltage barrier - and now: connect through RS and reduce the base voltage and current in Q3, thus taking Q out of saturation - and as a result the resistance (radiator - collector) at Q will increase, and the supply current and voltage will decrease to the safe value, which guarantees protection of the load from damage.

The resistance R is set and calibrated so that if a short circuit occurs in 21 or the load increases greatly, then D: becomes conductive, and due to the increase in the resistance (the emitter - the collector) of the transistor Q - and this of course will determine the output current and its voltage to the safe value.

Reducing aliasing: since the circuit contains two amplification components, which are (Q2, Q1), the circuit will be more sensitive to changes in the input voltage than the zener diode regulator circuit, as the irregular continuous voltage squiggles at the entrance to the circuit represent a rapid change in the value of the input voltage (50- 100 Hz) Therefore, the circuit elements treat these zigzags as any change in the input voltage and try to cancel it. Although aliasing is not completely eliminated, it is significantly reduced - which reduces the need to use regulated output filtering elements.

8-12 Three-way Voltage Regulator:

​​​​​​​It is a single piece composed of an integrated circuit silicon chip - (IC) that has only three terminals - terminal (1) is the input, terminal (2) is the output, and the third terminal (3) is the ground (Figure (12) 12).

This circuit contains all the elements necessary for voltage regulation and overload protection and also includes a large gain error amplifier, current limiting transistors and resistors with a reference voltage for series bypass transistors, and a common output voltage of 5 - 6 - 8 - 12 - 15 - 18 - 24 volts. It is used to feed individual integrated circuits. The load current may exceed 3 A.

The ground end is usually connected to the body of the device (chassis), and therefore it is not necessary to isolate the integrated circuit from the metal body - for the metal body to absorb the heat of the circuit directly - and this integrated circuit can be used as a control and tuning element in a transistor regulation circuit with high currents . The three-part regulation circuit is covered with a plastic or metal cover, as shown in the figure.