effect

1. Energy flow control

Q4 is turned on (energy storage) : When MOS tube Q4 is turned on, the power supply VIN passes through the inductor L8, causing L8 to store energy and the current to rise. At this time, D6 is reverse biased and cut off, blocking the output capacitor C11 from discharging to the ground, avoiding energy loss.

Q4 is turned off (energy release) : When Q4 is turned off, L8 generates reverse electromotive force, D6 is forward-conducted, and the magnetic field energy of L8 supplies power to the load through D6 and charges C11 to maintain the output voltage.

2. Avoid energy loss

If D6 is not connected to the circuit, Q4 is turned on, and C11 will discharge to the ground through Q4, resulting in capacitor energy waste, output voltage drop, MOS tube overheating or even damage, and circuit efficiency is greatly reduced. However, D6 is reversely cut off to cut off this path, ensuring that C11 energy is only supplied to the load, so that the L8 energy storage process is not disturbed.

(III) Achieving voltage boost

Energy storage (Q4 is on, D6 is off) : VIN supplies power to L8, the current of inductor L8 increases linearly, and the magnetic field energy accumulates.

Energy release (Q4 off, D6 on) : L8 and VIN voltage are superimposed to boost the load. D6 state switching ensures Boost.

The diode must meet the following requirements:

Withstand voltage : The reverse withstand voltage is greater than VOUT, leaving a 20% - 30% margin.

Current : The average forward current is greater than the maximum load current, and the peak current matches the L8 peak current to prevent overheating.

Speed : Choose fast recovery or Schottky diode (Trr < 100ns) to reduce switching losses.

Voltage drop : The smaller the forward voltage drop, the better, which reduces conduction loss.