DC stabilized power supply
The DC stabilized power supply is mainly composed of four parts: power transformer, rectifier circuit, filter circuit and voltage regulator circuit.
Power transformer
The power transformer is a soft magnetic electromagnetic component whose functions are power transmission, voltage conversion and insulation isolation. It is widely used in power supply technology and power electronics technology.
2. Rectifier circuit
A "rectifying circuit" is a circuit that converts alternating current electrical energy into direct current electrical energy. Most rectifier circuits consist of a transformer, a rectifier main circuit, and a filter. It is widely used in the field of DC motor speed regulation, generator excitation regulation, electrolysis, electroplating and other fields. The rectifier circuit usually consists of a main circuit, a filter, and a transformer. After the 1970s, the main circuit was composed of silicon rectifier diodes and thyristors. The filter is connected between the main circuit and the load to filter out the AC component of the pulsating DC voltage. Whether the transformer is set or not depends on the specific situation. The role of the transformer is to achieve a match between the AC input voltage and the DC output voltage and electrical isolation between the AC grid and the rectifier circuit.
The function of the rectifier circuit is to convert the AC voltage outputted by the AC step-down circuit into a unidirectional pulsating DC power. This is the rectification process of the AC power, and the rectifier circuit is mainly composed of a rectifier diode. The voltage after the rectification circuit is no longer an alternating voltage, but a mixed voltage containing a direct current voltage and an alternating current voltage. It is customary to call a one-way pulsating DC voltage.
3. Filter circuit
The filter circuit is often used to filter out the ripple in the rectified output voltage. It is usually composed of reactive components, such as a capacitor C connected across the load resistor, or a series inductor L with a load, and various complexes composed of capacitors and inductors. Filter circuit.
4. Voltage regulator circuit
A voltage regulator circuit is a circuit that maintains a constant output voltage when input voltage, load, ambient temperature, and circuit parameters change. This circuit provides a stable DC power supply and is widely used in a variety of electronic devices.
　 Main technical indicators of DC stabilized power supply
The technical specifications of DC stabilized power supply can be divided into two categories: one is the characteristic index, which reflects the inherent characteristics of DC stabilized power supply, such as input voltage, output voltage, output current, and output voltage adjustment range; the other is quality indicator. Reflects the advantages and disadvantages of DC regulated power supply, including stability, equivalent internal resistance (output resistance), ripple voltage and temperature coefficient.
1. Characteristic index
(1) Output voltage range
The output voltage range that can work normally under the conditions of DC regulated power supply operating conditions. The upper limit of this indicator is specified by the maximum input voltage and the minimum input-output voltage difference, and the lower limit is determined by the reference voltage value inside the DC regulated power supply.
(2) Maximum input-output voltage difference
This index characterizes the maximum allowable input-output voltage difference under normal operating conditions of the DC regulated power supply. The value depends mainly on the withstand voltage specification of the internal regulator of the DC regulated power supply.
(3) Minimum input-output voltage difference
This indicator characterizes the voltage difference between the minimum input-output required to ensure proper operation of the DC regulated power supply.
(4) Output load current range
The output load current range is also known as the output current range. In this current range, the DC regulated power supply should be able to meet the specifications given in the specification.
2, quality indicators
(1) Voltage regulation rate SV
The voltage regulation rate is an important indicator to characterize the performance of the DC stabilized power supply. It is also called the voltage regulation coefficient or the stability factor. It is used to characterize the stability of the output voltage VO of the DC stabilized power supply when the input voltage VI changes. The percentage change in the relative change in input and output voltage at unit output voltage.
(2) Current regulation rate SI
The current regulation rate is a major self-indicator that reflects the load capacity of the DC stabilized power supply, also known as the current stability factor. It characterization of the ability of the DC stabilized power supply to suppress the fluctuation of the output voltage due to the change of the load current (output current) when the input voltage is constant. Under the condition of the specified load current, it is usually measured at the unit output voltage. The percentage of the output voltage change value indicates the current regulation rate of the DC stabilized power supply.
(3) Ripple suppression ratio SR
The ripple rejection ratio reflects the suppression of the mains voltage introduced by the DC regulated power supply at the input. When the input and output conditions of the DC regulated power supply remain unchanged, the ripple rejection ratio is often the peak-to-peak value of the input ripple voltage. The peak-to-peak ratio of the output ripple voltage is expressed in decibels, but it can sometimes be expressed as a percentage or directly in the ratio of the two.
(4) Temperature stability K
The temperature stability of the integrated DC stabilized power supply is a percentage value of the relative change of the output voltage of the DC stabilized power supply within the maximum variation range of the operating temperature of the DC regulated power supply (Tmin ≤ Ti ≤ Tmax).
　 Five DC stabilized power supply circuit diagram
Circuit diagram 1:
The whole circuit is controlled by the single-chip microcomputer (AT89C51). The data port of P0 port and DAC0832 is directly connected. The CS and WR1 of DA are connected to P26, and WR2 and XFER are grounded, so that DA works in single buffer mode. The 11 pin of DA is connected to the reference voltage. By adjusting the adjustable resistor, the output voltage of the LM336 is 5.12V, so the resolution of the output voltage of the 8-pin of the DAC is 5.12V/256=0.02V, which means that the DA input data terminal Increase by 1, the voltage increases by 0.02V.
Circuit diagram 2:
Capacitor step-down 5V DC regulated power supply, the following power supply, can provide up to about 55mA current:
Capacitor step-down 5V DC regulated power supply below this power supply, can provide up to about 120mA current:
0-300v adjustable output circuit, this circuit in order to isolate from the mains plus a 1:1 transformer, you can directly enter the mains without this transformer, of course, the safety will be reduced, but does not affect the use.
Circuit diagram three:
Circuit operation principle: C1 and C2 and power supply filter TLP form a TI-type low-pass power supply filter circuit to eliminate power frequency interference. The pre-regulation of the pre-stage uses a three-terminal regulator 7818. Two large electrolytic capacitors C7.C9 are connected to the input and output terminals of the 7818 to obtain a DC voltage with a small ripple, and also two small-capacity Electrolytic capacitors C8 and C10 are used to improve the load transient response and suppress the high frequency self-excitation caused by the external circuit of the device itself. The post-stage voltage regulation includes a precision voltage source composed of LM399, an error voltage amplifier composed of a general-purpose operational amplifier LM741, and an amplification buffer voltage regulating circuit composed of transistors V1 and V2. The temperature stabilizer of the LM399 is powered by a +18V power supply. The voltage reference voltage is 6.95V, the dynamic internal resistance is 0.52, the noise voltage is less than 0.7uV, the temperature coefficient is 0.000000 3/*C. The long-term working stability is 20PPM/th. hour. From the circuit diagram. As can be seen, the LM741 is connected to a high gain DC differential amplifier circuit with negative feedback. R4 and R5 form a voltage sampling loop, and the sampling signal VG is sent to the reverse input end of the LM741, and compared with the reference voltage signal VREF of the non-inverting input terminal, the generated error control signal is outputted by the sixth pin and buffered by the transistor V2. The adjustment tube V1 is driven to dynamically change the tube voltage drop of V1 to obtain a stable voltage output. The RP is a WXD] precision wirewound potentiometer that rotates the position of the RP center tap to continuously adjust the output voltage of the regulated power supply. Under the parameters in the figure, the output voltage range is 1.0-15V, and the output current is less than or equal to 500mA. When the external circuit voltage is changed from 156 to 260V, the change of only 1LSB is measured with a 51/2 digit digital multimeter , and the ripple voltage is less than 0.2mV.
Circuit diagram four:
The circuit is shown in Figure 1 (click here to download the schematic). Since the maximum output current of the LM317 is 1.5A, and the power consumption is excessive when the voltage difference between the input and output terminals is too large, the Q1 high-power transistor is used to expand the output current. RP is a wirewound potentiometer, which can precisely adjust the output voltage. Q2 is set to avoid the RP contact poor contact, which causes the output voltage to be higher than the set voltage. In general, Q2 is cut off. Once the RP contact is open, Q2 is turned on by the bias voltage supplied from the RP, causing the voltage at the regulation terminal to drop, thereby making the output voltage low. R1, R2, R3, Q3 and K2 form a current range detection circuit. When the load current reaches a voltage drop of 0.3V on the resistor R1 or R2 or R3, Q3 is turned on, so that Q4 is turned on, JK is pulled, and the output is output. When it is cut off, LED2 goes out and LED1 turns on, indicating that it is in the overcurrent limit state. Pressing K1 can restore the normal output state, and the C6 of the thyristor G pole acts as an anti-drying effect, which can reduce the false trigger of the thyristor.
In addition to the working status indication, LED2 is also the load when the power supply is unloaded, so that the output voltage is not much different between the load and the no load. The voltmeter in the circuit can be replaced with a multimeter.
The component type and value of the power supply are marked in the figure and can be used without adjustment after assembly. It should be noted that Q1 should be equipped with a high-power transistor and a heat sink. The rectifier bridge D1 should be larger than 3A. LED1 and LED2 use different color LEDs. The resistance values ​​of R1, R2 and R3 can be determined according to their own needs, and the switch K2 should be in good contact, otherwise it will affect the use.
Circuit diagram five:
The voltage regulator circuit is composed of a power switch SI, a power transformer T, a rectifier bridge stack UR, a capacitor C-C3, a three-terminal voltage regulator integrated circuit IC1, an IC3, and a resistor RO-RI0.
The output voltage control circuit is composed of a control button S2. a reset button S3, a resistor RI-R31, a transistor V-VIO, a light-emitting diode VL-VU0, and a decimal counter/divider integrated circuit 1C2. Due to space limitations, the circuit is RI2-RI9. R22-R29. VL2-VL9 and V2-V9 are not shown. Turn on Sl, AC 220V voltage after T step-down, UR rectification, C and C2 filtering, one way as the regulator input voltage is added to the IC's 3 feet, output after IC voltage regulation; the other way is regulated by IC3 + 9V, as the working power of IC2.
After IC2 is powered on and reset, its YO terminal (3 pin) outputs a high level, so that v is turned on, R is grounded through the internal resistance of V, and the voltage is connected to the voltage regulator circuit (R2-RI0 is turned on by V). Short circuit to ground) The output voltage after 1C voltage regulation is +1.5V; at the same time, VU lights up, indicating that the output voltage value is +1.5V.
Press S2, CP2 (14 pin) of IC2 will input a high-level pulse, 1C2 will start counting, its Y terminal will output high level, make V2 turn on, RI and R2 will connect to the voltage regulator circuit (R3-RIO After V2's conduction internal resistance is short-circuited to ground, the output voltage of the IC rises to +3V, and VL2 lights up; at the same time, the YO terminal of 1C2 becomes low level, V is cut off, and VL is extinguished.
Pressing S2 continuously, the YO-Y9 output of 1C2 will output a high level in turn, and the IC output voltage will rise at 1.5V steps, and the corresponding LED will illuminate, indicating the output voltage value. When the Yg terminal of 1C2 outputs a high level, VIO is turned on, R1-RIO is all connected to the voltage regulator circuit, and the output voltage of the IC is +1.5V; at the same time, VLO is lit, indicating that the output voltage is +I5V.
After pressing the reset button S3, IC2 is forced to reset, its M terminal outputs a high level, and the output voltage of 1C is +1.5V. Changing the resistance of RO- RIO can change the level of the regulated output voltage. Component selection RO- RIO selects 1/2W precision metal film resistor RII-R31 selects 1/4W metal film resistor or carbon film electricity C and C2 select aluminum electrolytic capacitor, C voltage value is 35V, C2 The withstand voltage is 25V.
VL-VUO uses p3mm or p5mm LEDs. UR selects 2A, 50V rectifier bridge stack. VI-VIo selects S8050 or C8050, 3DG8050 silicon NPN transistor.
IC selects LM317 type three-terminal adjustable voltage regulator integrated circuit; IC 2 selects CD4017 or MC14017 type decimal counting/distributor integrated circuit; IC 3 selects LM7809 or CW7809 type three-terminal regulator integrated circuit.
T selects lOW, the secondary voltage is 18V power transformer.
S1 selects 250V. The contact current capacity is SA power switch; S2 and S3 select micro-close button.
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