This circuit is Low dropout 5V regulator that use LM317 as main. The voltage input is 5.1V DC is converted into 5V output,while the maximum output current is 2A by TIP41 increase current.
How it works
From this circuit: Low dropout voltage regulators circuits that can converted voltage input from 6V to 5V output,they uses transistors as main components.
When we need a 5VDC power supply, but we has a voltage input as the level is voltage input low 5.1V only. Which does not possible difficult. But this circuit can help us. See on figure below! is LM317 Power supply that has Low Volt drop across lower 0.1V only.(The voltage input about 5.1V to 12V)
The LM317 is highly popular IC (3 termial possive adjustable regulator IC). The voltage drop across adj pin and output pin is about 1.25V ,and next LED1,LED1 glow which has voltage across both LED are 3.6V(1.8V+1.8V) and they serves as display power on of this circuit.
So, Voltage output around of 5 volts. These components will maintain voltage Regulated at output as feature of LM317 and both LED there. Normally this circuit take voltage input about 5.1V to 12V. Besides still have Q1-TIP42 PNP transistor sevres as increasing current up to 2A