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May 27 2019

Principle and Application of DC Regulated Power Supply

Introduction

This article mainly introduces how does the DC regulated power supply work, how to use it and some knowledge of maintenance. Let's take a look at this article.


Article Core



Principle,application and maintenance



Purpose


Introduce how does the DC regulated power supply work, how to use it and some knowledge of maintenance



Application


Scientific research, production, teaching and maintenance departments.



Keywords


Principle, Application, DC Regulated Power Supply, Circuit




This video shows how to use a power supply


Almost all electronic circuits need a stable DC power supply. In the verification and maintenance of the indicator instrument, in addition to the appropriate standard instrument, there must also be a suitable DC power supply and regulating device. When supplied by the AC power grid, it is necessary to convert the AC power supplied by the power grid into stable DC power. After rectification and filtering, AC becomes DC. Although it can be used as DC power supply, however, due to the fluctuation of grid voltage, the DC voltage output after rectification will also fluctuate. At the same time, the load current in use is also constantly changing, some of which vary greatly. When it flows through the internal resistance of the rectifier, it will produce a fluctuating voltage drop on the internal resistance, so that the output voltage will fluctuate with the fluctuation of the load current. If the load current is small, the output voltage is high, the load current is large, and the output voltage is low. The voltage fluctuation of DC power supply will cause the instability of circuit work. For precise measuring instruments, automatic control or electronic computing devices, it will cause measurement and calculation errors, and even affects the normal operation. Therefore, a voltage stable DC power supply is usually needed.

Transistor DC regulated power supply can be used as DC power supply for all kinds of transistor instruments, electronic computers, automatic control systems and equipment. Precise voltage-regulated and current-regulated power supply can also be used as a voltage-regulated and current-regulated power supply for the verification of some electrical instruments. Therefore, transistor DC regulated power supply is a necessary instrument commonly used in scientific research, production, teaching and maintenance departments.

I Principle of DC Regulated Power Supply

1.1 Block Diagram and Working Principle

The typical circuit block diagram of transistor series DC regulated power supply is shown in figure 1. It consists of rectifier filter circuit, series voltage regulated circuit, auxiliary power supply and protection circuit.

II Application of DC Regulated Power Supply

The use of DC regulated power supply is very simple. When it is in use, attention should be paid to the polarity of the required DC voltage. If a positive voltage needs to be output, the output end of the DC voltage regulated power supply "-"  connects with the "ground" end of the electrical equipment, and the terminal "+" should be connected to the required positive voltage terminal. If you need to output negative voltage, you need to reverse the above wiring method. Before electrifying, measure it with a multimeter to check whether the output voltage meets the requirements, so as to avoid excessive voltage damage to the electrical equipment.

In order to make the electrical equipment work properly and not to affect the stable and reliable operation of the electrical equipment because of the poor performance of the DC power supply, it is best to test it simply before acting on the regulated power supply. The main contents of the test are: the regulation range of the output voltage, the stability degree, the ripple voltage and the overcurrent protection and so on.


III Maintenance of DC Regulated Power Supply

3.1 Maintenance Procedures

3.1.1 Preliminary Surface Examination 

All kinds of voltage regulated power supplies are generally equipped with overload or short circuit protection fuses and input and output terminals. You should first check if the fuses are fused or loose, whether the terminals are loose or short-circuited to the ground, and whether the gauge needle of the voltage indicator is jammed. Then open the casing cover to see if the power transformer has scorched taste or mildew, and whether the resistance and capacitance have obvious damage phenomena, such as scorching, mold breaking, liquid leakage, cracking and so on.


3.1.2 Measurement of Rectifier Output Voltage 

In all kinds of regulated power supply, there is one or more groups of rectified output voltage. If these rectified output voltage has a group of abnormal, then the regulated power supply will have a variety of faults. Therefore, when overhauling, it is necessary to first measure whether the rectified output voltage is normal or not.


3.1.3 Test Electronic Device 

If the output of the rectifier voltage is normal and the output voltage stabilization is abnormal, it is necessary to further test whether the performance of the adjusting tube, amplifying tube, etc., is good, whether the capacitance has breakdown, a short circuit or an open circuit. If a device with damaged or variable value is found, normally the regulated power supply can be restored to normal after updating.


3.1.4 Check the Working Point of the Circuit 

If the rectifier voltage output and related electronic devices are normal, the operating point of the circuit should be further checked. For the transistor, there should be a certain working voltage between the collector and the emitter, and the bias voltage between the base and the emitter should meet the requirements and ensure that it works in the amplification area.


3.1.5 Analysis of Circuit Principle 

If the voltage of an operating point of a transistor is found to be abnormal, there are two possibilities: one is that the transistor is damaged; the other is caused by the damage of other components in the circuit. At this time, it is necessary to carefully analyze the causes of the problems according to the circuit schematic diagram, and further identify the damaged and variable components.

3.2 Common Examples of Troubleshooting of Voltage Regulated Power Supply

3.2.1 There is voltage stabilization but no voltage regulation 

When using a regulated power supply, it is usually to start preheating, then adjust the output voltage "rough adjustment" potentiometer, observe whether the voltage regulation function and adjustment range are normal, and finally adjust to the required power supply voltage value, and connect to the load. If the voltage is normal when there is no load, but after the load is connected, the output voltage decreases. If the possibility of external circuit fault is eliminated, the fault is that the voltage regulated power supply has no voltage regulated effect.

During maintenance, the on-off condition between the collector and the emitter of the high-power adjusting tube can be measured by a multimeter. If no problem is found, the rectifier diode can be further inspected for damage. As long as a rectifier tube is damaged, the full-wave rectifier becomes a half-wave rectifier. When there is no load, the large capacity filter capacitor can still provide enough rectifier output voltage to ensure the voltage regulation function of the stable voltage output. After connecting to the load, the rectified output voltage immediately decreases, and the voltage at the stable voltage output terminal also decreases and lose the function of stabilizing the voltage.


3.2.2 The output voltage is too high, and there is no function of voltage regulation and voltage stabilization 

Under the condition of no load, the output voltage of transistor DC regulated power supply is larger than the specified value, and there is no voltage regulation and voltage stabilization, the fault may occur because of the following reasons:

— The collector and emitter of one of the composite adjustment tubes is breakdown or short-circuited, and the rectifier output voltage is directly added to the voltage regulation output through the short circuit transistor, and is not controlled by voltage regulation and voltage stabilization.

— The collector or emitter of the sampling amplifier tube is on or off, and the composite adjusting tube is directly under the negative voltage of the auxiliary power supply Dz, and the base current is very large, so that the internal resistance between the emitter and the collector of the adjusting tube becomes very small. The voltage of the rectifier output is added directly to the stable voltage output terminal.


3.2.3 The voltage output of each gear is very small and there is no voltage regulating effect 

The failure may occur because of the following reasons:

— There is no rectifying voltage output from the main rectifier

— The voltage of the auxiliary power supply Dz is zero, resulting in the adjustment tube not working.

— The c-e of the sampling amplifier tube breaks through the short circuit in reverse, resulting in the adjustment tube not working.


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