1, the role of this resistor is to play a current limiting protection role, when the input voltage is too high, to protect the regulator block. Oxide film resistance is characterized by good heat resistance, so oxide film resistance is generally used. As long as the heat dissipation problem can be solved, other resistors can also be. Voltage stabilizationWhether the block input is a series resistor depends on the situation, the resistor will consume power, and bring trouble to heat dissipation.
2, I think it is better to series one, since the voltage is already known, there is a voltage drop of 15 volts on 317, which is indeed too large. Understand the maximum current output, to ensure that 317 has 4 volts of voltage drop can work well. The power of the resistors in series should be appropriate. Since it is an adjustable power supply, the output is relatively to change, the calculation is good.317 heat reduction, good heat dissipation, in order to durable. Below 30 volts, the voltage should not be a problem.700 ohms in series feel greatly. <3, this resistor is called the pull-down resistor, when the two op-amps are output low, both diodes are in the cutoff state, the regulator diode will not be on, if there is no "pull-down resistor", the entire node is in a high impedance state, the output level is uncertain, in some conditions will not be able to obtain a low level.
4, when the voltage on the regulator reaches its voltage regulator value, its dynamic resistance is very small, that is, the voltage increases a little bit, the current increases a lot, the more obvious this characteristic, the better the voltage regulator effect.
5, after the power supply is burned out, the output voltage will be reduced to no more than 6V, or even 0V; If the power supply does not burn out, the output is still maintained at 6V, which is equivalent to r replacing the role of resistance, playing a current limiting role. If the internal resistance of the power supply is small and the power is strong, the internal power consumption of the power supply Im*Im*r is not enough to make the power failure, then the test tube can withstand it, the results are described in 1 above.
A simple regulated power supply circuit can be made with a triode as shown in the figure: component parameters vary according to the required regulated voltage and current.
[1] Dual power supply, select combined output, series structure. The leftmost red is V, the rightmost black is V-, and the red and black in the middle are ground. After the multimeter test, the dual-power amplifier circuit test can be carried out. [2] When only a single power supply is needed, directly adjust the main circuit to 24V, short-circuit the first group of red and black, and adjust the protection current. Then put the red, black - power your board.
The simplest except for resistance step-downThe parallel voltage regulator is the series voltage regulator power supply. However, whether it is resistance step-down or series voltage regulation, they are linear power supplies with large power consumption and heat consumption. To a series voltage regulator circuit: the transistor can be more than 100V power tube, such as C207TIP31C, etc., magnification 30~50, if the magnification is small, to reduce the resistance of R. To have enough heat sink, there is a heat dissipation of 5~6W at 100mA output.
The output voltage of the power supply meets the requirements of the highest voltage and the maximum current. All loads of different voltages must be common. When converting high voltage to low voltage, if voltageWhen the reverse breakdown, in a certain current range (or in a certain power loss range), the end voltage is almost unchanged, showing voltage regulation characteristics, so it is widely used in regulated power supplies and limiting circuits.
plus a qualified radiator. Reduce the input voltage to reduce the loss of power, but at the cost of reducing voltage regulation performance.
The LM317 is an adjustable three-end voltage regulator capable of delivering over 5A current in the output voltage range 2V to 37V, making it very easy to use. The LM317 is used as an integrated three-terminal regulator block with variable output voltageConvenient and widely used integrated regulator block. There are many models of LM317 series regulator block: such as LM317HVH, W317L and so on.
Because the three-terminal fixed integrated voltage regulator circuit is easy to use, it is often used in electronic production. In practical applications, a sufficiently large radiator should be installed on the three-end integrated voltage regulator circuit (of course, it is not necessary under the condition of low power). When the temperature of the voltage regulator is too high, the voltage regulator performance will deteriorate or even be damaged.
can inhibit the disturbance of the input voltage high-power regulator chip High-power regulator chip , but due to the maximum working current limit of the regulator tube High-power regulator chip , At the same time, the output voltage can not be arbitrarily adjusted high-power regulator chip , so the circuit is suitable for the output voltage does not need to be adjusted, the load current is small, and the requirements are not highIn the case of the rate regulator chip , the circuit is commonly used to supply power to the chip with low supply voltage requirements.
BP2822 is a high precision LED constant current control chip for non-isolated step-down LED power supply systems, suitable for a full range of AC voltage inputs or DC voltage inputs of 12 ~ 600V. The package form is DIP8 plastic seal, with 1 pin as ground, 2 pin as line voltage compensation input, 3 pin as power supply, 4 pin as internal high voltage MOS tube source, 6 pin as internal high voltage MOS drain, and 8 pin as current sampling end.
The following two items are used for referenceTake the exam. SC5832 is a domestic high current synchronous 2A chip using SOT23-5 small package. A metal-oxide-semiconductor field-effect transistor (MOSFET) with very low RDS internal resistance of 80 ho. The input operating voltage is 5V to 5V, and the output voltage is 0.6V and adjustable to 5V. The continuous load current output of 2A can ensure the stable operation of the system in all states.
Can be SG3525A, SG3527A, KA3525A, TL494, etc. DCDC represents a DC power supply, such as a dry battery or a car battery. Domestic useThe 220V power supply is an AC power supply (AC). If a converter can convert one DC voltage (0V) into another DC voltage (5V or 0V), this converter is called a DC/DC converter, or called a switching power supply or switch regulator.
1, ◆TO-220-TO-220 package appearance (Transistor Outline Package is a kind of in-line package, which is often used in high-power transistors, small and medium-sized integrated circuits, etc. ◆7812 series integrated voltage regulator circuit High power regulator chip , if the printing side towards themselves, from left to right is the high power regulator chip : "Vi; GND; Vo; Housing and pin 2 ". ◆L7912 is a negative polarity three-terminal voltage regulator chip.
2, the word towards itself, pin down, from left to right input, grounding, output; 7912 word towards itself, pin down, from left to right is ground, input, output.
3, depending on the current required by your applied circuit, two tubes can definitely replace the premise that the power consumption of the ST L7812CV is less than the LM7812, that is, the output current of the former is less than the latter. The big horse cart is the same as the little horse cart; The L7912CV can replace the LM7912.
4, because the double 25V rectifier comes out and is equipped with a large capacitor, the no-load voltage is more than double 30V, from 30V to 12VAmong them, 18V, in order to ensure sound quality, so do not use DC-DC to depressor, or use LDO.
5, L7812CV and LM7812 only different manufacturers, other electrical indices are completely consistent, are output +12V1A. The L7912CV is the same as the LM7912, but it has a negative output voltage, i.e. -12V.
NoPin is input, pin 2 is ground, and pin 3 is output. Pin 7912:2 is the input, pin 1 is the ground, and pin 3 is the output. 7812:7812 is a forward voltage regulator integrated circuit, that is, 7812 to input a positive voltage greater than 15v at its input end, and there is a stable positive 12v output at its output end.
protel99 is generally no CW7812, you have to make your own parts library.
and 7912 two are positive and negative polarity output 12V three-end voltage regulators, are foot down, there are symbolsFacing yourself, the left foot and middle foot enter DC 24v, and the middle foot and right foot exit positive or negative 12v. Note: The middle pin of 7812 must be connected to the negative electrode of the incoming power, the output is the negative electrode of the middle foot, and the right foot is 12v; 7912 Contrary.
◆7812 series of integrated voltage regulator circuit, if the printing side towards themselves, from left to right is: "Vi; GND; Vo; Housing and pin 2 ". ◆L7912 is a negative polarity three-terminal voltage regulator chip.
and 7912 is not a triode, is a three-terminal voltage regulator chip, 7812 is the output of positive 12V, 7912 is the output of negative 12V, the pin definition is as follows: pay special attention to the pin definition is not the same.