Advanced Electronics Techniques: Fundamentals of Electronic Circuits

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Advanced Electronics Techniques: Fundamentals of Electronic Circuits

Circuit Analysis · Practical Application of Voltage Regulation and Charging Circuits

I. Simple Electronic Circuits

1. 7805 Three-Terminal Voltage Regulator Integrated Circuit

The 7805 is a commonly used three-terminal voltage regulator integrated circuit, as shown in Figure 14-2. As long as components are selected according to the specified values and soldered correctly, it outputs a stable 5 V voltage without requiring adjustment. The components labeled $C_1$ and $C_2$ in the diagram are both power supply filter capacitors. The $C_1$ has a voltage rating of 10 V, while the $C_2$ requires a voltage rating of ≥16 V. This regulated power supply provides a fixed output voltage of 5 V with a maximum output current of 1.5 A.

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Figure 14-2 7805 Three-Terminal Voltage Regulator Integrated Circuit

2. Battery Charging Circuit Analysis

The battery charging circuit is shown in Figure 14-3. Control selector switch S regulates the charging current, offering two positions: 100 mA and 50 mA. The brightness of the light-emitting diode (LED) indicates the position of switch S and the magnitude of the charging current. $R_5$ serves as the LED's current-limiting resistor, restricting the current flowing through the LED to a specified value.

Analysis of Working Principle:

When switch S is positioned at the 100 mA setting shown in Figure 14-3, the base voltage of transistor T stabilizes at 6V, with its emitter voltage approximately 5.4V. Dividing this voltage by the sum of resistors $R_4$ and $R_2$ (The current through the LED in series with $R_5$ is approximately 5 mA and is neglected in this estimation), yielding a current of approximately 100 mA. Thus, the battery charging current is 100 mA. Similarly, if switch S is set to the 50 mA position, the battery charging current is 50 mA.

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Figure 14-3 Battery Charging Circuit

II. Finished Product Requirements

(1) Component leads must be soldered perpendicular to the circuit board; they must not be tilted or slanted. Components should be arranged logically, neatly, and aesthetically.

(2) Solder joints are smooth with appropriate solder quantity. Solder flow is clean and uniform.

(3) Can implement circuit functions.

(4) After completing the soldering, properly store and maintain the soldering iron.