1. Voltage regulator is introduced.
The commonly used voltage stabilizers on the main board are 1117 1084U 1085U 1086N 1087U EH11A3804 L1284N RT9164 and so on. The 1117 regulator (see figure 1) is the Low DropOut regulator, LDO, on the motherboard that adjusts the input voltage to a stable voltage output. This adjustment is a step-down adjustment, and the input voltage must be higher than the output voltage.
The 1117 regulator has two types of fixed output and adjustable output. The surface of the voltage stabilizer is marked by fixed output (see Fig. 1) and the unmarked one by adjustable output. In the actual circuit, it is also possible to detect whether there is a positive signal in the first pin of the regulator, if the resistor is connected between the one pin and the second pin, the output is adjustable, and the direct grounding of the pin without resistance is a fixed output.
2. Application of regulator.
Adjustable output voltage regulator 1117 as shown in figure 2, 3-pin input, 2-pin output, 1-pin grounding. IN is the input pin, OUT is the output pin, and ADJ is the voltage adjusting pin, which is grounded by resistance and connected with the output pin through a resistor. When used on the motherboard, the output voltage of the two pins is adjusted by the magnitude of the R1 and R2 resistances connected by the one pin. The output voltage of LM1117 is adjustable at 1.2V and the input voltage is up to 12V.
3. Precision regulator 431, 432.
The 431 is an internal device with a 2.5V precision reference source, while the 432 is an internal integrated 1.24V precision voltage stabilizer. The common 431 has three pins: cathode, anode, and ref, as shown in figure 3.
Working buried: cathode and anode conduction when the reference pin voltage is higher than 2.5 V, and anode cutoff when the reference pin voltage is less than 2.5 V.
LM431 is used to generate 2.5V reference voltage on the motherboard. As shown in figure 4, VCC3 outputs a 2.5 V VREF25 reference voltage after passing through R166 current limitation through 431 stable output.