Connect pins 1 and 3 to the positive terminal, and pin 2 to the negative terminal of the battery. In parallel, the input voltage is about 3v (dry battery), and the output is 3V. The pressure difference is too small. Connection is 2.5V.
It involves the working principle of the voltage regulator circuit. To regulate the voltage, it is necessary to use the resistor to sample from the output electrical end of the power supply, and then the sampled voltage information through a triode (or multiple triode constitute multistage amplification) for inverting the amplification, and then the amplified voltage signal final feedback (transmission) to the input control end of the power supply, so as to control the voltage down when the output voltage of the power supply is to rise. On the contrary, when the output voltage of the power supply is about to drop, the control voltage rises to ensure that the output end of the power supply can be stable in a stable voltage range. And now many circuits put the above sampling inverting amplification multiple functions integrated in an integrated circuit 431, by a 431 integrated tube to complete the above sampling inverting amplification function, so 431 is called precision sampling inverting amplifier, it can be said that 431 is an integrated block, do not mistake as a triode to use oh.
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The 431 has three pins, which are the input voltage reference terminal R, the ground terminal A and the output voltage terminal K. You must know where it is in the circuit, where the foot is the ground foot, which is the voltage sampling input reference point, and which is the 431 output level end, and then connect the three feet of 431 to the circuit board. This is required to have a certain circuit basis. If there is no circuit basis, it can be directly connected with a good 431 according to the pin position of the original 431. You don't have to worry about connecting or not connecting.
This requires you to decide what circuit to use according to your use. Small current 5V regulated power supply, only a few simple resistors and a TL431 can be satisfied; High current is to use several resistors and a TL431 plus a power tube to achieve. I hope it was helpful.