Ion Laser - Power Supplies

Power Supplies

• NPN passbank like the Spectra-physics 270 supply
• MOSFET switchers like the Omnichrome 150 supply
• Early switchers used NPN_PNP Pairs, (i.e. American Laser or HGM Medical)
• IGBT will be seen more in days to come
• Switched resistor (Spectra Physics)
• Non-switched resistor (Home-made, typically a water heater element)
• Water-cooled resistor (Laser Ionics etc.)
• Phased SCR power supplies similar to long xenon arc lamps are used in medical lasers to reduce expense (Coherent)
• Power on Demand power supplies are used for pulsed medical ion laser systems, these power supplies consist of a large capacitor bank charged by a switching supply to enable multi watt lasers to run off common single phase power supplies in doctor's offices.
• A typical air-cooled Argon Tube needs an equivalent series resistance of ~6 Ohms when running @ 10 amps off 117V power. The plasma in an ion laser, unlike a Helium Neon Laser, has a slightly positive resistance, but will still run away without ballasting. This is why ion laser supplies are very difficult to design. On a large frame laser, the plasma itself has an effective resistance of about -7 Ohms (Spectra Physics 171 Service Manual)