This is the power supply voltage without soft start, and the rise is very steep.

This is with soft start, and the rising edge becomes smoother.

Just by adding a capacitor and a resistor, you can achieve the circuit's soft start function. #HotspotEnginePlan#

When a power supply voltage is 5V and the load is a large capacitance, the power supply will instantly turn on, causing the voltage to rise to 5V instantly, leading to a very large charging current in the capacitor. If the power supply voltage is increased to 2.5V, this current will be much smaller, and soft start is needed at this time.

Soft start: Gradually turning on the power supply to limit the surge current during startup.

Here's a circuit found online that uses the charging time of capacitor C1 to turn on the MOSFET and achieve soft start functionality.

When the input signal is low or high impedance, the power supply +5V is powered up, the base of Q2 is pulled low to ground, the transistor is turned off, and then MOSFET Q1 is turned off.

This is because the power supply +5V is unstable, and the power supply cannot open to output to the subsequent circuit.

At this point, when the power supply +5V is just powered up, the gate and source of the MOSFET are at the same potential, that is, Vgs=0, and Q1 is turned off.

The role of resistor R4 here is to prevent Q2 from floating when the input signal is high impedance.

After the power supply is powered up, both GS ends are at 5V, and Vgs remains at 0.

At this point, when the input signal is set to high level, approximately 3.3V, the base of Q2 is 0.7V, and the current is 0.26mA:

(3.3V - 0.7V) / base resistor R3 = 0.26mA

When Q2 is saturated and turned on, Vce≈0;

Capacitor C1 charges through resistor R2, and the voltage at the end of C1 connected to the gate gradually decreases from 5V to 0V, increasing the Vgs voltage; Q1 MOSFET slowly opens, and finally fully opens, Vgs=-5V, realizing soft start.

This is the current flow when the MOSFET Q1 is turned on:

When the capacitance is larger, the voltage is higher, the time is shorter, and the current is larger, causing a surge current to form.

This circuit uses the charging time of capacitor C1 to turn on MOSFET Q1 and achieve soft start functionality.

However, a large capacitance is just one of the reasons for the formation of surge currents; other loads can also cause surge currents.