I am trying to understand the soft power switch operation of a LED lamp I dissembled. The circuit of the lamp is depicted below.
The switch S1 can be considered as a momentary on switch (SPST). The power P-mosfet Q1 is used to drive the LED. Q1's base is controlled from NPN (Q3) transistor which when in on state pulls it down. The values of resistors are accurate as indicated in actual circuit. The values of capacitors are not valid as I am not able to measure them, but yet I have difficulty understanding the operation.
As opposed to other soft latch circuits, this one uses just two transistors. And there is no feedback from drain of Q1 to base of Q3. If I have transfer accurately (*with the exception of capacitances) the circuit on diagram it seems a very simple design.
In simulation I can't find the exact capacitor values to make it work as the actual one.
The lamp actually works, as when pushing momentarily switch 1 the lamp turns on and when pushing again lamp turns off.