Practical Technology of Integrated Voltage Regulator

    Abstract: In recent years, with the rapid development of integrated circuit technology, the development of integrated voltage regulators has also accelerated, resulting in the rapid development of power supply technology design technology, and thus integrated voltage regulators have been widely used. This article introduces several common and practical application methods of integrated voltage regulators, and gives a detailed description of the issues that should be paid attention to in the selection and design of their devices.

    Keywords: Integrated voltage regulator, voltage source, adjustable output

At present, integrated voltage regulators have developed to hundreds of varieties and many types. According to its different classification methods, it can be divided into series type, parallel type and switching type according to the structure; it can be divided into fixed type and adjustable type according to the output voltage type; it can be divided into three-terminal integrated voltage regulator according to the pin connection method. and multi-terminal voltage regulators; according to the manufacturing process, they can be divided into semiconductor integrated voltage regulators, thin film hybrid integrated voltage regulators and deposited film hybrid integrated voltage regulators; according to the working mode of the circuit, they can be divided into linear integrated voltage regulators and switch integrated voltage regulators. Stabilizer.

1 Commonly used integrated voltage regulators

1.1 Multi-terminal debugable integrated voltage regulator

The sampling resistor and protection circuit components of this kind of voltage regulator need to be connected externally, and there are many external terminals, so it is suitable for different usage situations. Its output voltage can meet the requirements of different output voltages. Most of the products currently produced in China are of this type.

1.2 Three-terminal integrated voltage regulator

This type of voltage regulator has three terminals: input, output, and common ground (or adjustment terminal), and comes in two types: fixed and adjustable. In addition, it is divided into positive voltage and negative voltage output types. For example, the CW7800 series is a three-terminal fixed positive voltage output integrated voltage regulator. Its output voltage has 7 levels of 5, 6, 9, 12, 15, 18, and 24V. The maximum output current of this series of products can reach 1.5A. Similar products include the CW78M00 and CW78L00 series. In addition, the CW7900 (CW79M00, CW79L00) series is a two-terminal fixed negative voltage output integrated voltage regulator. Its output voltage series value and output current are the same as the CW7800 (CW78M00, CW79L00) series. This type of product has the advantages of easy use, stable performance, and low price, so it has been widely used and has basically replaced the voltage stabilizing circuit composed of discrete components.

The CW117 series (including CW117, CW217, and CW317) are three-terminal adjustable positive voltage output integrated voltage regulators, while the CW137 (including CW137, CW237, and CW337) are three-terminal adjustable negative voltage output integrated voltage regulators. The voltage regulation and load regulation indicators of this type of integrated voltage regulator are better than those of fixed integrated voltage regulators, and they also have overheating, current limiting and safe operating area protection functions. Its main performance is as follows:

●Output voltage adjustable range: 1.2~37V;

●Maximum output current: 1.5A;

●Voltage regulation rate: 0.01%/V;

●Load regulation rate: 0.1%;

●Allowable range of output and input voltage difference: 3~40V.

1.3 Tracking integrated voltage regulator (positive and negative voltage integrated voltage regulator)

There are many circuits that use positive and negative power supplies (such as operational amplifiers). They usually use a positive voltage regulator and a negative voltage regulator to form a positive and negative power supply. However, using a tracking integrated voltage regulator to form a positive and negative power supply is effective. It is more ideal, because the tracking voltage regulator can not only ensure that the positive and negative output voltages are always balanced, and the center point is always the ground potential, but also has automatic tracking capabilities.

2 applications

2.1 Fixed output voltage source

A fixed-output regulated power supply can be easily formed by using a three-terminal fixed output integrated voltage regulator. The voltage regulator model can be determined based on the required output fixed voltage value and maximum output current. For example, if you need a regulated power supply with an output voltage of 15V and a maximum output current of 1A, you can choose the CW7815 device.

The design circuit of a fixed positive voltage output regulated power supply is shown in Figure 1. In the figure, UI is the DC input voltage obtained after rectification and filtering, and U0 is the output voltage of the regulated power supply. In order to improve the ripple voltage and suppress the instantaneous overvoltage of the input, a capacitor CI is connected to the input end. Generally, the capacity of CI is 0.33 μF . At the same time, capacitor C0 is connected to the output terminal to improve the transient response of the load. The capacity of C0 is generally 0.1 μF . In order to reduce the output ripple voltage, a large-capacity electrolytic capacitor can be connected to the output end, so that once a short circuit occurs at the input end, the internal circuit adjustment tube of the integrated voltage regulator can be discharged in time. In order to prevent damage, a diode should be connected across the input and output to provide a shunt path for the discharge of the output capacitor, which can effectively protect the adjustment tube inside the integrated voltage regulator.

If you need to output negative voltage, just replace the CW7800 in Figure 1 with the CW7900. Pay attention to the polarity of the power supply to get a negative voltage power supply. The CW7800 and CW7900 series can also be used to form a regulated power supply with positive and negative symmetrical outputs.

2.2 Expand the output current and voltage source

The output current of the three-terminal integrated voltage regulator has certain limits (such as 1.5A, 0.5A, or 0.1A, etc.). If you want to expand the output current, you can achieve it by connecting an external high-power transistor. The circuit connection method as shown in picture 2.

RS and VT2 in Figure 2 are short circuit protection links. Under normal load, Ic1Rs is less than the turn-on voltage of VT2, and VT2 is cut off. At this time, I0=I0xx+Ic1. When overloaded or short-circuited, the Ic1Rs value is greater than the turn-on voltage of VT2, VT2 turns on, UCE2=Ic1Rs+UBE1, when IC1 increases, UBE2 decreases causing UBE1 to decrease, thus limiting the The current of T1 tube plays an overcurrent protection role. Since the circuit uses an external triode to expand the current, it will have a certain impact on the voltage stabilization accuracy of the integrated voltage regulator, so care should be taken during use.

2.3 Increase the output voltage voltage source

If a higher output voltage is required in actual work, it can also be improved based on the output voltage of the original three-terminal fixed integrated voltage regulator. The circuit is shown in Figure 3 (a) (b).

Figure 3(a) The circuit uses the voltage regulator VDZ to increase the output voltage. (The diode VD at the output end is a protection diode) and its output voltage is U0=U0'+Uz.

Figure 3(b) The circuit uses resistors to increase the output voltage, and its output voltage is U0=(1+R2/R1)U0'

The above two circuits for increasing the output voltage are relatively simple, but the voltage stabilization performance may be reduced.

a. Adjustable power supply composed of fixed integrated voltage regulator

The output voltage of a three-terminal fixed output voltage integrated voltage regulator is usually not changeable, but under certain circumstances, the output voltage value can be changed through an external circuit. The specific circuit is shown in Figure 4. Its output voltage is:

U0=U0' ×R3/(R3+R4) ×(1+R2/R1)

If the resistor R1+R2=R3+R4 in the figure, and R3=1k Ω, R4=9kΩ , then U0=(R3/R1)×U0'

When R2=0, the circuit output voltage can be adjusted starting from 0.1U0'. The smaller the starting voltage, the wider the output voltage adjustment range.

b. Adjustable power supply composed of adjustable integrated voltage regulator

The adjustable voltage stabilizing circuit composed of an adjustable integrated voltage stabilizer is shown in Figure 5. In order to ensure that the voltage stabilizer can work normally when no load is applied, the current flowing through the current R1 cannot be too small. Generally, IR1=5~10mA, so R1 should be 120~240 Ω . As can be seen from the figure, the output voltage is

U0=UREF(1+RW/R1)+IARW

Its UREF is the reference voltage (UREF=1.25V) between the output terminal (3) and the adjustment terminal (2), and IA represents the current flowing out from the adjustment (IA=50 μA ). Adjusting RW can change the output voltage. Capacitor C1 in the circuit can be used to improve the ripple suppression ratio, and VD1 and VD2 play a protective role.

3 Selection of integrated voltage regulator

When selecting an integrated voltage regulator, several factors such as its performance, usage and price should be taken into consideration. Currently, there are four types of integrated voltage regulators on the market: three-terminal fixed output voltage type, three-terminal adjustable output voltage type, multi-terminal adjustable output voltage type and switching type.

When the output voltage is required to be a fixed standard series value and the technical performance requirements are not high, a three-terminal fixed output voltage integrated voltage regulator can be selected. The CW7800 series should be selected for the positive output voltage, and the CW7900 series should be selected for the negative output voltage. Since the three-terminal fixed integrated voltage regulator is simple to use, does not require any adjustments and is relatively low-priced, it has a wide range of applications.

When high voltage stabilization accuracy is required and the output voltage can be adjusted within a certain range, a three-terminal adjustable output voltage integrated voltage regulator can be selected. This voltage regulator also has positive and negative output voltages and output currents. Choose Attention should be paid to the electrical parameter characteristics of each series of integrated voltage regulators.

For multi-terminal adjustable output voltage integrated voltage regulators, such as five-terminal adjustable integrated voltage regulators, because it has a special current limiting function, it can be used to form a voltage stabilizing source and a stabilizing current source with control functions. This is an integrated voltage regulator with higher performance and cheaper price.

An important advantage of the monolithic switching integrated voltage regulator is its high power utilization rate. The CW1524, CW2524, and CW3524 series currently produced in China are integrated pulse width modulation voltage regulators, which can be used to form a switching regulated power supply. .

4 Precautions when using

Integrated voltage regulators have been widely used in power supplies. In order to better utilize its advantages, you should pay attention to the following issues when using them:

First: Don’t connect the wrong pins. For multi-terminal voltage regulators, connecting the wrong leads will cause permanent damage; for three-terminal voltage regulators, if the input and output are connected reversely, when the voltage at both ends exceeds 7 volts, the voltage regulator may be damaged.

Second: the input voltage U1 cannot be too low or too high. If the voltage is too low, the performance of the voltage regulator will be reduced and the ripple will increase; while if the voltage is too high, it will easily cause damage to the integrated voltage regulator.

Third: Do not exceed the rated power consumption. For multi-terminal voltage regulators, when the output voltage is adjusted to a lower level, it can prevent the voltage drop on the adjustment tube from being too large and exceeding the rated power consumption. Therefore, when outputting a low voltage It is better to reduce its input voltage at the same time.

Fourth: To ensure safe use, a protection circuit should be added to prevent instantaneous overvoltage, input short circuit, and load short circuit. For large current voltage regulators, attention should be paid to shortening the connecting wires and installing sufficient heat dissipation equipment.

5 Summary

Using an integrated voltage regulator simplifies the power supply circuit and improves the resulting performance. As long as you choose the appropriate integrated voltage regulator and pay attention to its usage, you can form a practical circuit that meets various requirements. It can be seen that the use of integrated voltage regulators in power supplies will become more and more widespread.