Lighting fluorescent lamp on a bench (with 400V/1A power supply)For a very long time fluorescent lamps were a bit of a mystery for me - how they should be preheated, what's up with negative resistance, striking - all this was not clear. Today, when LED dominate the world (except for applications with UV harder than 365nm) I got to figure this out. Main ingredient here is new product of Chinese engineering - HSPY-400-01 - 400V/1A DCDC power supply.
Heating filaments from one side, ~100mA:
If we crank up current a bit (to 220мА) - heating alone is enough to excite mercury and get white fluorescence. This mode of operation is very dangerous to the lamp (this is exactly the way I fried filament on the other side):
Now lamp could be started from ~150V DC, discharge current is 100mA with ~42V voltage drop. DCDC power supply is not fast enough to support discharge due to negative resistance of the lamp, so ballast resistor is required. Minimal resistor for stable discharge appeared to be ~74Ω. With lamps of this type one can disable filament heating during discharge - this will improve efficiency and expand lifetime.
Without heating lamp could not be striked even by 400V DC, higher and higher filament current reduces striking voltage to 100-150V. But that could be further lowered by preheating both filaments and going AC using H bridge.