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electronic ballast

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Fahime

New Member
Hi,
Herewith is a schematic of an electronic ballast for 2of 36W FPL lamps. It's working well. But there is a small problem with it:
When I connect it to the mains, it turns on quickly. but the problem is that after just 1 second it gets alittle bit darker. This change in light is not so noticable but I like to know the reason and fix it if possible.
If I disconnct it and reconnect it immidiately, that won't happen. Actually it turns on in the darker state.
I appreciate you for your assist.
 

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Sceadwian

Banned
Probably just the way the starter works on that ballast. Why are you making your own ballasts? Commercial ballasts are incredibly cheap.
 

Hero999

Banned
It will probably blow the tube if it operated it at that brighness continuously.

To be honest, I haven't analysed the circuit to see how it works.

Why are you doing this? Is it just for educational purposes?
 

Sceadwian

Banned
10X probes on a scope and a current sense resistor would show you what's going on visually if you have a scope available.
 

tcmtech

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Most Helpful Member
I suspect the circuit puts a fair more amps into the tube heater elements than it uses during actual running conditions. It may very well be a time lag in the starting circuit that is causing the flare. Its not tapering back on the amp limit fast enough.
 

mneary

New Member
I haven't analyzed it carefully but it does look to me like Hero and TCM have mentioned. It appears that the output power is higher until Q3 is turned on. Maybe Q3 changes the oscillation frequency. Time constant of R6, R6', and C11 works out in the neighborhood of a second. This may be to either strike the arc, heat the filaments, or heat the gas in the tubes, or all of the above.

I also agree that it does not need to be "fixed".

Note: If anyone plans to build this thing, the 'ground' symbol on the diagram is just a common point and is not Earth.
 
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