How to understand the circuit diagram - power circuit reading map points and examples

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Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

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SMD aluminum electrolytic capacitor

Power circuit reading diagram points and examples

A power circuit is a relatively simple but widely used circuit in an electronic circuit. When you get a power supply circuit diagram, you should: 1 Decompose the entire power supply circuit in the order of “rectification-filtering-stabilization” and analyze it step by step. 2 In the step-by-step analysis, the main circuit and auxiliary circuit, main components and secondary components should be distinguished, and their functions and parameter requirements should be clarified. For example, in a switched regulated power supply, the inductor and the freewheeling diode are the key components. 3 Because transistors have NPN and PNP types, some integrated circuits require dual power supplies, so a power supply circuit often includes different voltage values ​​and several sets of outputs. The values ​​and polarities of the output voltages of each group must be distinguished when reading the picture. Carefully distinguish the polarity of the transistors and electrolytic capacitors during assembly and repair to prevent errors. 4 Familiar with some customary techniques and simplified drawing. 5 Finally, the entire power supply circuit is fully integrated from front to back. This power circuit diagram is also understood.

Example 1 Electric blanket temperature control circuit

Figure 5 is an electric blanket circuit. The switch is in the low temperature range at the "1" position. After 220 volts, the electric power is connected to the electric blanket through the diode. Because it is half-wave rectification, the pulsating direct current of about 100 volts is applied to both ends of the electric blanket. The heat is not high, so it is insulated or low temperature. When the switch is turned to the "2" position, the 220V mains is directly connected to the electric blanket, so it is a high temperature file.

Example 2 High-voltage electronic mosquito killer

Figure 6 shows a small-current DC high-voltage electric mosquito killer using the voltage doubler rectification principle. The 220 volt AC is rectified by quadruple voltage and the output voltage is up to 1100 volts. This DC high voltage is applied to the parallel wire mesh. The bait is placed under the net, causing a short circuit when the fly stops on the net, and the high voltage on the capacitor kills the fly through the body discharge of the fly. After the fly corpse falls, the capacitor is charged again and the grid is restored to high voltage. This high-voltage grid has a small current and is therefore harmless to humans.

Because insects have phototaxis at night, if you put a 3 watt fluorescent lamp or a small black light behind the grid, you can trap mosquitoes and harmful insects.

Example 3 Practical regulated power supply

Figure 7 is a practical regulated power supply. The output voltage is adjustable from 3 to 9 volts and the output current is up to 100 mA. This circuit is a series-type regulated power supply circuit. It should be noted that: 1 The drawing of the rectifier bridge is different from that of Figure 2 (c). In fact, it is a bridge rectifier circuit. 2 This circuit uses a PNP-type manifold, so the output is a negative voltage and the anode is grounded. 3 Replace the Zener diode with two common diodes. The forward voltage drop of any diode is essentially constant, so a diode can be used instead of a Zener. The forward voltage drop of the 2AP diode is about 0.3 volts, the 2CP type is about 0.7 volts, and the 2CZ type is about 1 volt. Two 2CZ diodes are used as reference voltages. 4 The sampling resistor is a potentiometer, so the output voltage is adjustable.

A circuit capable of amplifying a weak signal is called an amplifying circuit or an amplifier. For example, the key component in a hearing aid is an amplifier.