Hello,
I've developed a small high-voltage power supply that works well except for one thing.
You can check out my Github repository here: https://github.com/stefaweb/audio-psu/tree/main/HV-MODULE-UC3845-1.0
I wanted to implement a softstart in the last prototype, but unfortunately, it won't work. I've tried several softstart circuits, from the simplest to the most advanced, without success. Unfortunately, I only have a straight curve when I start it. With the current circuit, I should get a curve of 1 to 3 seconds.
None of them work, as if they weren't taken into account. I'm going around in circles. Either I have a major error that I haven't seen, or the softstart won't work with the UC3845B for some reason. A friend of mine made one with a UC3842, and it works with the same softstart circuit.
Does anyone have any ideas?
Regards,
Stef.
I've developed a small high-voltage power supply that works well except for one thing.
You can check out my Github repository here: https://github.com/stefaweb/audio-psu/tree/main/HV-MODULE-UC3845-1.0
I wanted to implement a softstart in the last prototype, but unfortunately, it won't work. I've tried several softstart circuits, from the simplest to the most advanced, without success. Unfortunately, I only have a straight curve when I start it. With the current circuit, I should get a curve of 1 to 3 seconds.
None of them work, as if they weren't taken into account. I'm going around in circles. Either I have a major error that I haven't seen, or the softstart won't work with the UC3845B for some reason. A friend of mine made one with a UC3842, and it works with the same softstart circuit.
Does anyone have any ideas?
Regards,
Stef.
Attachments
How about you put the soft start at the 24v input with a mosfet to turn the circuit on and off. with a delay.
Or at the ic supply pin, so the mosfet won't have to run high currents.
Or at the ic supply pin, so the mosfet won't have to run high currents.
Hello,
I finally found the problem. It was really simple. I was testing the board with a load of only 1mA. The minimum for regulation to work. If I increase the load, for example, to 60mA at 350V, the softstart works.
However, I'm currently adjusting the softstart to have a longer delay (between 1 second and 1 minute). To do this, I increased resistor R4 to 10MΩ and added a footprint for a capacitor on the top of the PCB. I left the 1uF SMD C13 below as base value. It will be enough to add a capacitor above the chosen value depending on the desired softstart duration.
The project is almost finished. I still have a few things to check, and then I'll publish the Gerbers on the Github repository.
Regards,
Stef.
I finally found the problem. It was really simple. I was testing the board with a load of only 1mA. The minimum for regulation to work. If I increase the load, for example, to 60mA at 350V, the softstart works.
However, I'm currently adjusting the softstart to have a longer delay (between 1 second and 1 minute). To do this, I increased resistor R4 to 10MΩ and added a footprint for a capacitor on the top of the PCB. I left the 1uF SMD C13 below as base value. It will be enough to add a capacitor above the chosen value depending on the desired softstart duration.
The project is almost finished. I still have a few things to check, and then I'll publish the Gerbers on the Github repository.
Regards,
Stef.
Attachments
Hello,
I've uploaded the TUBE-HV-PSU-45W project (the large mother board) to my Github repository at the following address:
https://github.com/stefaweb/audio-psu
The Gerber files are available in the file TUBE-HV-PSU-Gerber-1.0.zip and the BOMs in the file TUBE-HV-PSU-BOM.html (to be opened with an Internet browser).
The HV module will follow in a few days. I'm waiting for new UC3845A chips from TI to verify the compatibility. The prototypes were developed with the UC3845B from ONSEMI because I had problems sourcing the original TI chips.
I've run simulations of the cost of the HV module with only the SMD components assembled by JLPCB. For 5 units, it costs €17 each (without the OPA810, which is too expensive at JLPCB). The complete module with TH components and the OPA810 costs around €45 (sourcing from Mouser or Digikey). The Wurth transformer is cheaper at Digikey, by the way.
Regards,
Stef.
I've uploaded the TUBE-HV-PSU-45W project (the large mother board) to my Github repository at the following address:
https://github.com/stefaweb/audio-psu
The Gerber files are available in the file TUBE-HV-PSU-Gerber-1.0.zip and the BOMs in the file TUBE-HV-PSU-BOM.html (to be opened with an Internet browser).
The HV module will follow in a few days. I'm waiting for new UC3845A chips from TI to verify the compatibility. The prototypes were developed with the UC3845B from ONSEMI because I had problems sourcing the original TI chips.
I've run simulations of the cost of the HV module with only the SMD components assembled by JLPCB. For 5 units, it costs €17 each (without the OPA810, which is too expensive at JLPCB). The complete module with TH components and the OPA810 costs around €45 (sourcing from Mouser or Digikey). The Wurth transformer is cheaper at Digikey, by the way.
Regards,
Stef.