A Chinese "beauty skin therapy" thing
https://www.ebay.com/itm/Ultrasound-Facial-Body-Skin-Massager-Pain-Therapy-Ultrasonic-Machine-beauty-Age/142544969567?hash=item2130579f5f:g:0vYAAOSwd0BVyGueThe inside looks line this
The driver board with the mains transformer:
The driver board closeup (top):
The driver board closeup (bottom):
The uC board (bottom):
My schematic of the main driver part of the driver board (the power supply part and the relay control part are not included, the transducer part is a Butterworth-Van Dyke equivalent circuit):
Oscilloscope captures of the operation:
CH1 - base of Q1 (input from the uC board)
CH2 - collector of Q3 (output to the transducer)
CH3 - base of Q3
The stated resonant frequency of the transducer is 1.1Mhz (~1.05 MHz measured)
The output is PWMed to control output power:
A closeup of the measurement (CH1 is about 3V max):
My questions about the circuit at the moment are:
1. How the "voltage doubling" on CH2 is achieved from the input 39V to the output 92V?
2. What is the purpose of Q2 and the circuitry around it?
3. Why the base of Q1 is out of phase with the base of Q3?
4. What is the purpose of L2 and C5? (L2 is the big vertical heat-shrunk inductor on the top right on the photo, reading 68uH on the board)
There's probably an explanation of a similar circuit somewhere (a patent or something), but I've not found it yet.