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PTC-SIDAC preheating circuit

PTC-SIDAC preheating circuit


This is a video of an 8W electronic instant start fixture that I've modified to preheat the cathodes of the tube.
I've added a PTC resistor in series with a SIDAC diode.
A SIDAC diode is like a switch which is enabled only when a threshold voltage is exceeded and is reset when the current fall under a another threshold (in this case on every semi cycle).
The breakdown voltage must be chosen > of the running lamp voltage and < of the ignition voltage of the lamp.
After the preheat phase the SIDAC block the current flowing in the ptc which mean:
- No power is vasted.
- No instant start if the lamp is short power cycled (valid if the lamp is powered on for at least 30s).
- the PTC is not "cooked" by remaining hot for all the running time of the tube.
- The PCB solder joint of the PTC are not stressed as much by the thermal cycles because in the ~2s when the PTC is powered the heat has not enough time to propagate trough the leads and reach the solder joint.

In the video is visible a cold startup whith preheating (nothing extraordinary), after running ~45s (in the meantime the PTC is cooled down) a short power cycle shows that the tube is preheated. After this another short power cycle, this time without the 45s delay, shows that the PTC is not cooled enough to provide a good preheating.

I've used the sidac MKP1V120 for the 8w lamps and the MKP3V240 for the 13w lamps(the MKP1V240 would be better because it is smaller but it wasn't in stock at digikey)

Mini-Lynx.jpg osramdulux.jpg youtube_MAArf1G1QVA.jpg STARTE2MOSSCH.JPG

Light Information

Light Information

Lamp
Lamp Type:T5
Electrical
Wattage:8W

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Album name:Kappa7 / Electronic ballast circuits
Keywords:Gear
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Date added:Jan 19, 2014
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dor123
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Jan 20, 2014 at 12:13 AM Author: dor123
The preheating looks much like that of the microcontroller based real programmed start ballasts (Preheat bright than dimming down before starting the lamp).
I think that the Ingenium ballast of Megamen operates in a similar manner, as including a real programmed start electronic ballast inside a CFL, can make it very expensive.

I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

I only working with the European date format (dd.mm.yyyy).

I lives in Israel, which is a 230-240V, 50hz country.

Medved
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Jan 20, 2014 at 01:55 AM Author: Medved
The "ingenium" uses frequency control preheat, the required control chips come even in 8-pin format, so can fit there well. But as far as I know, for the phase-cut dimmable products they are using some wide SOIC chip (again, clearly analog: I was able to identify an OPAMP connected in the lamp current control circuit, gate driver, analog preheat timer capacitor)

The thing is, even with the VDR or SIDAC, which let the PTC to cool down during lamp operation, for really frequent switching like on PIR sensors the lamp is frequently operated too short before the next restart, so you need really fast reset of the preheat timer. And that mean the timer component can not be thermal based (PTC,...), but pure electrical (e.g. charging a capacitor)

And by the way it is not any microprocessor, but a bunch of rather simple analog circuitry with one or two flip-flops (but all integrated within a single IC), what control the operating state of most programmed start controllers.
One of the reason is the voltage requirement (15V supply for gate drive, 600V floating circuit capability), what does not mix well with dense digital and flash memory process steps (and the microprocessor based ballast IC will require both features on the same IC).
Other reason is, the functionality is usually quite fixed, so beside some parameter fine tuning via external component values need no programability.

The microprocessors are used only in digital interfaces of dimmable ballasts (DALI interface, DoRS cycle readout,...) and what they do is just receive the command (DALI frame and/or count the short switching cycles) and convert the data to a dimming control voltage for the main ballast IC (forming the reference voltage for the OPAMP based current control circuit in the main ballast IC).

No more selfballasted c***

Kappa7
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Jan 20, 2014 at 02:32 AM Author: Kappa7
The preheat behavior (Preheat bright than dimming down before starting the lamp) depends mainly by the characteristic of the ptc resistor, even some simple cfl with only the ptc act like this. I think it depends how sharply the resistance raise with the temperature just before the "switch" effect of the ptc.
Medved
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Jan 20, 2014 at 02:42 AM Author: Medved
It strongly depend on how the current depend on the resistance in the circuit and how evenly the filaments are heated along their length.
Mainly voltage mode heating in some programmed start ballasts tend to overheat some parts of the filament, when the rest is still cold.
And the selfoscillating circuits with the PTC tend to operate at higher current during the preheat.

No more selfballasted c***

adamrvlx
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Sep 17, 2019 at 05:19 AM Author: adamrvlx
Please, could you send me the diagram? Thanks
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