Series DC regulated power supply circuit schematic diagram

Series DC regulated power supply circuit principle

The structure of a series DC regulated power supply is shown in the figure below (a). It can be seen that a series DC regulated power supply usually consists of six parts: transformer, rectifier filter, adjustment device, comparison amplifier, reference power supply and sampling. Some regulated power supplies also have overload or short-circuit protection devices.

As can be seen from the following figure b), the circuit uses transformer T to reduce 220V to 10V, and then through VD1~VD4 bridge rectification, the AC 10V is converted into pulsating DC, which is filtered by capacitor C1, and then goes through voltage stabilization, amplification, and sampling to make the adjustment tube VT2 work, and the output DC Uo is 6V. By adjusting the size of the sampling resistor RP, the output voltage U0 can be changed within 6V, and the output current of the circuit is 200mA.

Its voltage stabilization process is: when the output voltage changes, the amplifier amplifies the error signal through the "sampling" of the resistor divider and compares it with the reference power supply, and sends it to the base of the adjustment tube to adjust its tube voltage drop to achieve the purpose of stabilizing the output voltage. Generally speaking, the greater the amplification factor of the amplification link, the higher the stability.

The following is an analysis of the series DC regulated power supply block diagram shown in Figure a) above:

1. Reference power supply, reference voltage

The reference voltage should be a DC voltage with high stability. Otherwise, if the reference voltage value changes, even if the input remains unchanged, it will cause the output voltage to change, affecting the stability of the output voltage.

At present, the reference voltage is often obtained by using a silicon Zener diode VS and R5, as shown in Figure b) above. The key to the Zener diode circuit is to select a current-limiting resistor, the resistance of which should ensure that when the input voltage is minimum, the current flowing through the Zener diode is not less than the minimum current to maintain a stable voltage; and when the input voltage reaches its maximum value, it should ensure that the current flowing through the Zener diode is not greater than its maximum allowable current.

2. Sampling

The sampling link is a resistor voltage divider, which consists of R1, R2, and RP, as shown in Figure b) above. The task of the sampling link is to take out a part of the output voltage, add it to the comparison amplifier, and compare it with the reference voltage to detect the change value of the output voltage, and then control the adjustment link after amplification.

3. Comparator Amplifier

The comparison amplifier compares the voltage obtained by the sampling circuit with the reference voltage, then amplifies the difference between the two and controls the adjustment tube to stabilize the output voltage. It should be pointed out that the gain of the comparison amplifier will directly affect the quality index of the voltage-stabilized power supply. The simplest comparison amplifier is a single-stage DC amplifier, as shown in Figure b) above, VT1 constitutes a single-stage DC amplifier as the comparison amplifier link.

4. Adjustment

The adjustment link is the core link of the voltage-stabilized power supply, because the output voltage ultimately depends on the regulation of the adjustment link to achieve stability, and the maximum current that the voltage-stabilized power supply can output also mainly depends on the adjustment link.

The adjustment link is composed of the adjustment tube VT2 working in the linear region, and its base current is controlled by the output signal of the comparison amplifier. Since the output current of the regulated power supply must all pass through the adjustment tube, it should be ensured that the selected adjustment tube has sufficient power consumption and collector current.

Series DC regulated power supply circuit diagram

The series voltage regulator circuit is a type of DC voltage regulator. In fact, it was a commonly used DC power supply method before the emergence of the three-terminal voltage regulator. Before the emergence of the three-terminal voltage regulator, the series voltage regulator usually had an OP amplifier and a zener diode to form an error detection circuit, as shown in the figure below. In this circuit, the reverse input terminal of the OP amplifier is connected to the detection signal of the output voltage, and the forward input terminal is connected to the reference voltage Vref, Vs=Vout*R2/(R1+R2).

Since the amplified signal ΔVs is negative, the base voltage of the control transistor decreases, so the output voltage decreases. Under normal circumstances, Vref=Vs=Vout*R2/(R1+R2). The required output voltage value can be set by adjusting the ratio of R1 and R2.

The basic principle of the three-terminal voltage regulator is that the load size can be adjusted by replacing the transistor with a Darlington tube, etc. This type of series voltage regulator circuit can easily cause oscillations if the DC voltage regulated power supply is not handled properly.

Nowadays, engineers who do not have a certain level of analog skills generally do not use this method. Instead, they directly use an integrated three-terminal voltage regulator circuit to use the DC/DC conversion circuit.

The voltage regulator circuit of the Zener diode has a simple circuit structure, but has poor load capacity and low output power. It generally only provides a reference voltage for the chip and is not used as a power supply.

When selecting a Zener diode, it can generally be estimated according to the following formula: (1) Uz=Vout; (2) Izmax=()ILmax (3) Vin=（2-3）Vout This circuit has a simple structure and can suppress input voltage disturbances, but it is limited by the maximum operating current of the Zener diode and the output voltage cannot be adjusted arbitrarily. Therefore, this circuit is suitable for occasions where the output voltage does not need to be adjusted, the load current is small, and the requirements are not high. This circuit is often used to power chips that do not have high requirements for the supply voltage.

10 rules 3: Reference voltage source chip voltage regulator circuit

Another form of voltage stabilization circuit, some chips have relatively high requirements for the supply voltage, such as the reference voltage of AD DA chips, etc. At this time, some commonly used voltage reference chips are TL431, MC1403, REF02, etc. TL431 is the most commonly used reference source chip, a three-terminal adjustable shunt reference voltage source with good thermal stability.

Its output voltage can be arbitrarily set to any value within the range from Vref () to 36V using two resistors. The most commonly used circuit application is shown in the figure below, where Vo = (1 + R1/R2) Vref.

By choosing different values ​​of R1 and R2, any voltage output in the range of 1V to 36V can be obtained. In particular, when R1=R2, Vo=5V.