Electronic – What’s the difference in fluorescent lamps

The book, Practical Eco-Electrical Home Power Electronics published by Elektor has a chapter on CFL inverters with some circuit diagrams of reverse-engineered inverters and an engineering explanation of how they work. See Practical Eco-Electrical Home Power Electronics published by Elektor.

The fluorescent tube has different circuit models when lit and unlit and they correspond to two different resonant modes which the inverter must accommodate in its design. After tearing apart multiple CFLs, I find the design is well-standardized as given in the previous answer for battery-powered lighting, and as a half-bridge (preceded sometimes by a voltage doubler) for line-operated CFLs.

All these inverters are resonant and when the bulb is not lit, depend on its capacitance to set the resonant frequency. Once lit, the bulb has a low-value of resistance and a capacitor in series with the bulb determines the series resonant frequency.

The capacitor in old Fluorescent Starters is for EMI suppression. This is typically a fairly-small value - anywhere between 1n to 100n, depending upon who made your particular starter.

The capacitor may also reduce contact erosion on the starter contacts - I honestly don't know. But I do know that in olden days when everyone had an AM radio sitting on the kitchen counter, you could immediately tell if someone turned on a Fluorescent lamp that didn't have that capacitor inside the starter.