LM358 Circuit: Linear DC Regulated Power Supply (With Example)

Introduction

In today's society, people enjoy the great convenience brought by electronic equipment. And everyone knows that electronic equipment has a common circuit - power circuit. The requirement of electronic equipment for power supply circuit is to be able to provide continuous and stable electric energy to meet the load requirements. And it is usually required to provide stable DC power. The power supply that provides this kind of stable DC power is the DC stabilized power supply. At the same time, protection is also an important part. Therefore, leakage protection device is also an inevitable circuit demand. Leakage protection device is a kind of grounding protection device which is used to prevent accidents caused by electric shock and electric leakage. When the leakage current of the circuit or electrical equipment is greater than the set value of the device, or people and animals get electric shock, it can quickly cut off the accident power supply. It can avoid the expansion of the accident scope, and ensure the safety of people and equipment. Therefore, this article uses LM358, field-effect transistor, and operational amplifier to design and produce a low dropout, wide range linear DC power supply.

Catalog

I Design Scheme

This system is mainly composed of DC voltage regulator module, leakage detection module, turn off protection module, etc.

1.1 Regulated Power Supply Circuit

As shown in Figure 1, this circuit module uses LM358 as a stable amplifier, and uses P-channel MOS tube. LM358 consists of two independent, high gain, internally frequency compensated operational amplifiers, which can stabilize the output at 5 ± 0.05 v when the input voltage changes from 5.5 V to 25 V.

Figure 1. circuit of regulated power supply

1.2 Leakage Detection Circuit

The device of leakage protection requires that when the input voltage is 5V, the output voltage is not less than 4.6V. The maximum voltage at both ends of resistor R1 is 0.4V. The current of the leakage protection circuit works at 250mV. It is calculated that R1 resistance should not be greater than 1.6Ω, so we choose 1Ω resistance as the detection resistance. As Figure 2 shows, connect a 1 Ω resistor in the circuit. The current can be calculated by detecting the voltage change at both ends of the resistor. A subtraction circuit is used to amplify the voltage because it is too small. The amplified signal is much larger than the input offset voltage. Then use a voltage comparator to determine the leakage current. This circuit is stable and reliable. After testing, it has reached a high accuracy of voltage detection.

Figure 2. circuit of Leakage Detection

1.3 Protective Shut-off Circuit

R1 is the detection resistance and adjust its value slightly. When the leakage current of the circuit is 30mA, the voltage difference between the two ends of R1 is amplified and sent to the base of triode. The triode is turned on; the relay K1 is closed, the load supply is disconnected. When the leakage fault is eliminated, press the reset button S1, and the circuit will return to the initial state.

Figure 3. Protective Shut-off Circuit

II System Analysis and Test

2.1 How to test regulated power supply circuit?

Load R is 5Ω. When the input voltage changes from 5.5 to 25V, record and measure the output voltage, and observe whether the result changes in the range of 5± 0.05V. Calculate the voltage regulation rate. Su=|Uo2一Uo1|/Uo2×100 (Uo1 is the output voltage when the input voltage is 5.5V, and Uo2 is the output voltage when the input voltage is 25V)

2.2 How to test Leakage protection circuit?

The regulated power supply removes the 5Ω load and switches to the leakage protection file. At this time, the working voltage is 5V. Then connect a 20Ω load and connect a 330Ω adjustable resistor in the analog branch. To observe the reliability and sensitivity of the leakage protection circuit, connect a digital multimeter in series to monitor the analog leakage branch current.

III Results and Analysis

The test results of voltage regulation rate are shown in the table below.

Result Analysis:

According to the test, when the branch current reaches 29.6 mA, the relay will pull in and self lock, and disconnect the load. Adjust the branch current to 26mA, then press the reset button, and the circuit will return to normal detection state. After repeated tests, the circuit is reliable and stable, and meets the requirements of safe use. The error absolute value of action current = | 30-29.6l/30 × 100% = 1.3%.

IV Conclusion

This article summarizes the design of a DC stabilized power supply and leakage protection system based on LM358. After repeated debugging, the experimental results show that the data error is within ±0.002v, which is far less than the allowable error of other regulated power supply on the market, and meets the design requirements. The system is stable and reliable, which can meet the various needs of users.

Component Datasheet

LM358 Datasheet

FAQ