How to design several schemes of power supply circuit of single chip microcomputer with 7805?

Related information: 7805 Chinese information

7805

Regulated power supply

Circuit diagram:

Pin diagram of 7805

Circuit diagram of 7805 typical application:

78XX series integration

Regulator

The following figure shows a typical application circuit of the, which has a positive 5V output.

volts d.c.

Stabilized power supply circuit based on. IC adopts integrated regulator 7805, and C 1 and C2 are input and output terminals respectively.

filter capacity

, RL is

Load resistance

. When the output power is large, the 7805 should be equipped with a cooling plate.

The following figure shows the application circuit for increasing the output voltage.

Voltage regulating diode

VD 1 is connected in series between the two pins of the 78XX regulator and the ground, which can improve the output voltage Uo to some extent. The output voltage Uo is the sum of the output voltage of the 78XX regulator and the regulated value of the zener diode VC 1. VD2 is an output protection diode. Once the output voltage is lower than the regulated value of VD 1, VD2 is turned on, bypassing the output current, and protecting the output stage of the 7800 regulator from being damaged.

The following figure shows an application circuit whose output voltage can be adjusted within a certain range. Due to the function of R 1 and RP resistance network, the output voltage is increased, and the increase range depends on the ratio of RP to R 1. regulate

potentiometer

RP, the output voltage can be adjusted within a certain range. When RP=0, the output voltage Uo is equal to the output voltage of the 78XX regulator; When RP increases gradually, Uo also increases gradually.

The following figure shows the application circuit for amplifying the output current. VT2 is the external expansion rate tube, and VT 1 is the push tube. They are

Darlington

Connect. R 1 yes

Bias resistance

. The maximum output current of this circuit depends on the parameters of VT2.

The following figure shows the application circuit for increasing the input voltage. The maximum input voltage of 78XX regulator is 35v (40V for 7824). When the input voltage is higher than this value, the circuit shown in the following figure can be used. VT, R 1 and VD form a prefix-.

Voltage regulator circuit

Therefore, the voltage applied to the input of the 7800 regulator is constant at the regulated value VD (ignoring the b-e junction voltage drop of VT). The maximum input voltage at the Ui terminal only depends on the withstand voltage of VT.

Integrated regulators can also be used as

Constant flow source

. The following figure shows the 78XX voltage regulator.

Constant current source circuit

, its

constant current

Io is equal to the ratio of the output voltage of the 78XX regulator to R 1.

79XX series integrated voltage regulator is a commonly used three-terminal integrated voltage regulator with a fixed negative output voltage. Except that the input voltage and output voltage are negative, other parameters and characteristics are the same as those of 78XX series integrated regulators. The three pins of the 79XX series integrated voltage regulator are 1 pin as the grounding terminal, 2 pins as the input terminal and 3 pins as the output terminal.

The application circuit of 79XX series integrated voltage regulator is also very simple. The following figure shows the stabilized power supply circuit that outputs -5V DC. IC adopts integrated voltage regulator 7905, which should be equipped with heat sink when the output current is large.

Using 78XX and 79XX regulators at the same time can form a voltage stabilizing circuit with positive and negative symmetrical outputs. The following figure shows the 5v regulated power supply circuit. IC 1 adopts a fixed positive output integrated regulator 7805, IC2 adopts a fixed negative output integrated regulator 7905, and VD 1 and VD2 are protection diodes to prevent the integrated regulator from being damaged when one of the positive input voltage or the negative input voltage is not connected.