DIY a low dropout linear regulator

This low-dropout linear regulator (LDO) circuit uses a thin, depletion-type field-effect transistor (MOSFET) to achieve the main function of a low-dropout linear regulator. It can separate a 5V voltage with very small ripple from the existing 5V voltage with large ripple (low-dropout voltage regulation), and ensure a fairly high output to input ripple suppression capability. (Another way is to boost the voltage first, and then use a linear regulator to gradually reduce it.) The principle of this production circuit is shown in the figure below: The circuit mainly includes a virtual ground potentiometer generator TLE2425, an error amplifier, a feedback resistor network, etc. The basic working principle is: TLE24125 provides 2.5V precision bias for single power supply op amp LMC6462, the system is powered on, the circuit starts to start, the constant current source circuit provides bias for the entire circuit, IC1 reference source voltage is quickly established, the output voltage rises with the input voltage, when the output voltage is about to reach the specified value (4.55V), the feedback network composed of R1 and R2 sends the output feedback voltage to IC2 (pin 2), at this time the error amplifier IC2 amplifies the error signal between the output feedback voltage (pin 2 voltage, 2.5V) and the reference voltage (pin 3), and then adjusts it through the adjustment tube BSS139 (T1), when the input signal of the G pole of BSS139 is less than VT (channel clamping current), the pinch-off resistance between its drain and source will continue to change, thus forming negative feedback, ensuring that the output voltage is stable at the specified value. The main function of C1 is to filter out the AC component. Similarly, if the input voltage changes or the output current changes, this closed loop will keep the output voltage unchanged.

The input voltage of this circuit is 5V, and the output voltage is 4.55V. The circuit uses an NMOS field effect tube device BSSl39. When used, the gate is forward biased, the load is 10rnA, and the measured FET resistance is 38Ω.