CO2 power supply ballast resistor?

[pixpop]

Hello,

I've been told that there should be a ballast resistor between the power supply and the anode of the tube. This is a common requirement for gas discharge tubes, such as HeNe lasers. The resistor is used because the laser tube has negative resistance, and you need a positive resistance to cancel that out.

However, everything I've seen regarding the Chinese power supplies & sealed CO2 lasers indicates that no ballast resistor is necessary. The instructions that came with my power supply say to just connect the HV lead directly to the anode of the tube.

Has anyone seen one of these sealed CO2 tubes with a ballast resistor in the anode circuit? Or, does anyone know why the resistor is not needed?

Thanks,

Neil

[andyamp]

modern switching HT co2 psu's will be constant current if correctly desined.
so I would not expect to find a ballast resistor.
its the older Transformer type of psu that need ballast resistors.

[zax15uk]

Neil,

Chinese PSU/tube can be connected directly as indicated. They use switching power supplies so as Andy said you don't need a ballast.

Zax.

[pixpop]

Thanks andy, zax. This is what I thought, and you have confirmed it for me. I have a better understanding of powering the CO2 tube now.

Neil