Advice on Nd:YAG Flashlamp power supply

[zigunov]

Hi,

I was wondering if anybody could give some advice on my reverse engineering endeavors here... I found this (I believe, 600V) power supply made to charge/trigger capacitors for flashlamps used in Nd:YAG laser tattoo removal machines:

https://www.aliexpress.us/item/3256805411784901.html

I'm working on a custom Nd:YAG laser, which is why I really wanted to make this work. I got the supply in the hopes I may be able to figure out how to trigger it. I'm still somewhat puzzled so I figured maybe some of you may have this experience since there's literally no information about how this supply is supposed to be wired in the internet (at least, not in English...).

I attached a picture of the circuit board inside. The main terminals for AC input and 600V output for the capacitor charging (CAP+, GND) are well-labeled. Also, the flashlamp trigger (HV-J) is also labeled and is the screw terminal at the bottom right.

The control connector is a white header connector with 8 pins, but only 5 are connected (see figure at the bottom right). I labeled in the picture the terminals 12V, GND, TR, A and C. The TR terminal is clearly a trigger input, as it connects directly to the gate of a SCR through a small network (likely for overvoltage protection). From my understanding of how these supplies work, the control board requests a charging of the capacitor (for safety purposes, the capacitor is always discharged except just before the laser fires). When the capacitor needs to be charged, I believe something needs to happen to either A or C to tell the board to oscillate the CHARGING TRANSFORMER (blue ones on top right of picture, I'm not sure which one). After charging is done (which I believe is assessed by also, A or C as an output), then the trigger signal is sent to TR and the SCR shorts the TRIGGER CAPACITOR and the TRIGGER TRANSFORMER, generating a high-voltage spike (>20kV, I believe) at the HV-J terminal where the flashlamp is connected. This strikes an arc at the flash lamp and shorts the main capacitor connected to CAP+, firing the flash lamp with however much energy is stored in the capacitor.

This is as far as I was able to probe and figure out. I'm confused about what is the function of A and C and how that communication may happen. Input pin A seems to be connected to the SG3525, which seems to be a PWM regulator IC. Pin C, on the other hand, appears to be connected to the LM358 op-amp. Pin C measures 0.14V when I plug the board, which I reckon is an effective zero, and the voltage of the capacitor is indeed zero volts when I plug the board in. Pin A measures 3.3V when I plug the board in, which is rather strange.

I reckon pin A is supposed to start the charging process, while pin C is supposed to monitor the voltage of the capacitor, or the charging current. The resistor/capacitor network there is very dense and I couldn't probe it with sufficient accuracy to draw a circuit diagram there or even identify which pin exactly from each IC they are connected to. I tried putting a constant 5V on pin A but it doesn't seem to start charging the capacitor. When I ground pin A, it pulses the output voltage quickly to ~800V but it doesn't maintain it and in about <1s it returns to 0V (likely the RC discharge time).

I was just wondering if you had any ideas of maybe how this charging circuit is supposed to work. I am not familiar with the SG3525 IC, and from the datasheet I couldn't figure out whether this uses an enable/disable input or if I need to provide an actual oscillatory signal to it.

Any comments would be appreciated! I'll try to keep you updated if I find anything else. Thanks!!

[moffy]

It doesn't look like the PCB photo is attached.

[zigunov]

oh, dang it! Sorry! Now it is =)

[daisizhou]

Why do you need to reverse engineer this circuit board?
It looks to me like this is a PCB from China,In other words, you can get it at a very low price.
It could be from a medical device or a cosmetic laser,It looks like this device is not advanced or very simple

[zigunov]

If you read my post, I'm not trying to reverse engineer it to build another one; I just need to figure out how to operate it. There's no documentation about what are the expected signals at the inputs.

[daisizhou]

This type of power supply has a "pre-ignition" circuit,The flash lamp is lit by "pre-ignition", then the voltage decreases, the current increases, and enters the low voltage maintenance state.
You can search for an Israeli Phoenix laser. I remember there is a manual for it on the Internet. There is a block diagram on the last page.

[zigunov]

Apparently the manufacturer you mentioned makes CO2 lasers, but this supply is for a Nd:YAG pumped by a flash lamp. The specs are different, but most importantly, the control signals come from a digital touchscreen. An example of such a machine is this: (https://www.aliexpress.us/item/3256806988159318.html)

[Phil1977]

Many of these Laser PS somewhere have a connection for a safety key switch. Maybe that´s what you pulled down with your GND-connection so that the converter started.

[daisizhou]

Apparently the manufacturer you mentioned makes CO2 lasers, but this supply is for a Nd:YAG pumped by a flash lamp. The specs are different, but most importantly, the control signals come from a digital touchscreen. An example of such a machine is this: (https://www.aliexpress.us/item/3256806988159318.html)

Not CO2 laser, please see the last page of the link below
https://www.medwrench.com/documents/view/14195/alma-lasers-harmony-xl-new-service-manual-revc
Pages 125 and 126 have diagrams