High precision series regulated power supply design

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Factory direct 5050 yellow light LED 5050 yellow light 5050 yellow high quality high brightness

MOS power IC full range

TP-IP4220CZ6 5V 0.35PF breakdown voltage 6V SOT

The series-type regulated power supply is made of series-type regulated power supply. The voltage regulation precision is high, the internal resistance is small, the output voltage can be adjusted freely at 3-6V, and the output current is 100 mA, which can be used for general experimental lines.

1. Working principle The low-voltage alternating current of the power transformer T secondary is rectified by the rectifier diode VDl-VD4, and the capacitor C1 is filtered to obtain direct current and is delivered to the voltage regulator. The voltage regulation part is composed of composite adjustment tubes VT1, VT2, comparison amplifier tube VT3, voltage regulator diodes VD5, VD6 and sampling trimmer potentiometer RP and other components.
The voltage drop between the collector and emitter of the transistor is referred to as the tube voltage drop. The tube pressure drop on the composite adjustment tube is variable. When the output voltage has a decreasing trend, the resistance of the dynamic resistance between the collector and the emitter of the composite adjustment tube becomes smaller, and therefore, the voltage drop of the dynamic resistance Will decrease, so as to maintain the output voltage unchanged; when the output voltage has a tendency to increase, the resistance of the dynamic resistance between the collector and the emitter of the composite adjustment tube will become larger, so the voltage drop of the dynamic resistance will The change is large and the output voltage remains unchanged. It can be seen that the composite adjustment tube is equivalent to a variable resistor, and the output voltage remains substantially unchanged due to its adjustment. The adjustment of the composite adjustment tube is controlled by the comparison amplifier tube. The output voltage is divided by the trimmer potentiometer RP, and a portion of the output voltage is applied between the base of VT3 and ground. Since the emitter-to-ground voltage of VT3 is stabilized by diode VD5, it can be considered that the emitter-to-ground voltage of VT3 is constant. This is called the reference voltage.
This change in the VT3 base voltage reflects the change in output voltage. If the output voltage has a tendency to decrease, the voltage between the VT3 base and the emitter also decreases, which causes the collector current of VT3 to decrease and the collector voltage to increase. Since the collector of VT3 and the base of VT2 are directly coupled, the voltage of the VT3 collector increases, that is, the base voltage of VT2 increases, which causes the composite adjustment tube to be turned on, the dynamic resistance is reduced, and the output voltage is maintained. constant. Similarly, if the output voltage has a tendency to increase, the tube voltage drop of the composite adjustment tube is increased by the action of VT3, and the output voltage is maintained.
VD5 is regulated by the fact that the forward voltage drop does not substantially change with current when it is conducting forward. The forward voltage drop of different LEDs is different. The specific reference values ​​are as follows: the voltage drop of the red LED is 2.0-2.2V. The yellow LED has a voltage drop of 1.8-2.0V, and the green LED has a voltage drop of 3.0-3.2V. The normal current is about 20mA. R2 is a current limiting resistor that provides VD5 forward current. The reason for choosing LED as the reference voltage regulator is that it can be used not only as a reference voltage, but also because its illumination makes students more interested in production, and it is also easy to observe the presence or absence of the power supply voltage. Rl is the collector load resistance of the comparison amplifier VT3. At the same time, it is the bias current of the base of the composite adjustment tube.
C2 is provided to further reduce the AC component of the output voltage. The role of C3 is to reduce the AC internal resistance and ripple of the regulated power supply.

2. The components are selected as shown in the table below.

3. Installation, commissioning and testing
(1) Install components correctly according to the assembly drawing. (The following figure)

(2) After checking that the components are installed correctly, turn on the power.
(3) Turn the multimeter to the DC voltage range, and measure the rod at both ends of C3 (note the polarity of the rod), adjust the resistance of the RP, and make the voltage change between 3-6V.
(4) Connect to the load debugging. When the output is 3V, connect 300 load resistors. Comparing the resistance of the load resistor before and after the access, the output voltage should be less than 0.5V.