A voltage regulator is a device that stabilizes the output voltage. It is composed of voltage regulator circuit, control circuit, and servo motor. When the input voltage or load changes, the control circuit performs sampling, comparison and amplification, and then drives the servo motor to rotate, so that the position of the carbon brush of the voltage regulator changes, and the coil turns ratio is automatically adjusted to maintain the stability of the output voltage. 7805 is the most commonly used voltage regulator chip. It is easy to use. A DC voltage regulator can be input with a very simple circuit, and its output voltage is exactly 5v.

7805 voltage regulator power supply working principle

Zener diode VD1 is connected in series between pin 2 of the 78XX regulator and the ground, which can increase the output voltage Uo to a certain extent. The output voltage Uo is the sum of the output voltage of the 78XX regulator and the voltage regulator value of the Zener diode VC1. VD2 is the output protection diode. Once the output voltage is lower than the regulated value of VD1, VD2 is turned on, bypassing the output current to protect the output stage of the 7805 regulator from being damaged. The internal circuit of the 7805 three-terminal voltage regulator IC has the functions of overvoltage protection, overcurrent protection and overheating protection, which makes its performance very stable. Can achieve output current of more than 1A. The device has a good temperature coefficient, so the application range of the product is very wide. Local regulation can be used to eliminate noise effects, solving the dispersion problem associated with single-point regulation, and the output voltage error accuracy is divided into ±3% and ±5%.

1. 7805 regulated power supply circuit diagram

1. 3 ~ 25V voltage adjustable voltage regulator circuit diagram

The adjustable range of this regulated power supply can be adjusted arbitrarily between 3.5V and 25V, the output current is large, and the adjustable voltage regulator tube circuit is used to obtain a satisfactory and stable output voltage.

Working principle: After rectification and filtering, the DC voltage is provided by R1 to the base of the regulating tube, so that the regulating tube is turned on. When V1 is turned on, the voltage passes through RP and R2 to turn on V2, and then V3 is also turned on. At this time, V1, The emitter and collector voltages of V2 and V3 no longer change (its function is exactly the same as that of the Zener tube). By adjusting RP, a stable output voltage can be obtained. The ratio of R1, RP, R2 and R3 determines the output voltage value of this circuit.

Components selection: Transformer T selects 80W ~ 100W, input AC220V , output double winding AC28V. FU1 selects 1A, and FU2 selects 3A~5A. VD1, VD2 select 6A02 . RP uses an ordinary potentiometer of about 1W, with a resistance value of 250K ~ 330K , C1 uses a 3300μF/35V electrolytic capacitor, C2 and C3 use a 0.1μF monolithic capacitor, and C4 uses a 470 μF/35V electrolytic capacitor. R1 selects 180～220Ω/0.1W～1W, R2, R4, R5 selects 10KΩ, 1/8W. V1 selects 2N3055, V2 selects 3DG180 or 2SC3953, and V3 selects 3CG12 or 3CG80.

2. 7805 regulated power supply circuit diagram 5v

The circuit shown in the figure is a regulated power supply with an output voltage of +5V and an output current of 1.5A. It is composed of power transformer B, bridge rectifier circuits D1~D4, filter capacitors C1, C3, self-excitation capacitors C2, C3 and a fixed three-terminal voltage stabilizer (7805) very simply and conveniently.

The 220V AC mains is converted into AC low voltage through the power transformer, and then rectified and filtered by the bridge rectifier circuit D1~D4 and the filter capacitor C1, forming a voltage at both ends of Vin and GND of the fixed three-terminal voltage regulator KIA7805 . Stable DC voltage (this voltage often changes due to fluctuations in mains voltage or load changes).

After this DC voltage is stabilized by KIA7805 and filtered by C3, a DC output voltage with high precision and good stability is generated at the output end of the stabilized power supply. The stabilized power supply can be used as the power supply of TTL circuit or single-chip circuit. The three-terminal voltage regulator is a standardized and serialized general-purpose linear regulated power supply integrated circuit. With its small size, low cost, good performance, high reliability, and simple and convenient use, it has become the current application in regulated power supplies. One of the most widely used monolithic integrated voltage regulators.

7805 regulated power supply circuit diagram (1)

A special linear regulated power supply composed of 7805, 7905, and 7812.

As shown in the figure is a special power circuit. Although simple, this circuit generates three sets of DC voltages: +5V, -5V, and +12V from two identical secondary windings. Its characteristics are: D2, D3 are connected across the two sets of AC power sources E2 and E3, and play the role of full-wave rectification.

7805 regulated power supply circuit diagram (2)

The internal circuit of the 7805 three-terminal voltage regulator IC has the functions of overvoltage protection, overcurrent protection and overheating protection, which makes its performance very stable. An output current of more than 1 A can be achieved. The device has a good temperature coefficient, so the application range of the product is very wide. Local regulation can be used to eliminate noise effects, solving the dispersion problem associated with single-point regulation, and the output voltage error accuracy is divided into ±3% and ±5%.

7805 three-terminal voltage regulator IC should pay attention to the following matters in the circuit application:

The input and output pressure difference should not be too large. If it is too large, the conversion efficiency will decrease rapidly, and it is easy to break down and damage. The maximum input voltage cannot exceed 35 volts; the output current cannot be too large, and 1.5A is its limit. For high current output, the size of the heat sink should be large enough, otherwise it will lead to high temperature protection or thermal breakdown; the input and output voltage difference should not be too small, and the efficiency of voltage regulation will drop rapidly below 2V