Xenon arc lamp igniter problem

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The boost capacitor is 10000uF, and it is also the power supply's main filter capacitor. The power supply parallels a triple voltage multiplier (boost) with a normal bridge (main) rectifier. The circuit is current regulated by a pair of IRF250, so the initial series resistor the lamp sees is nearly nothing. The boost supply seems fine to me. BTW, the xenon lamp is merely 200W.

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I think it's more like a pulse transformer without load.

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It seems that the calculation/simulation of such circuits is very difficult for me. maybe the only way to repair this power supply is to do some experiment. I really don't want to buy lot's of high-priced HV capacitors and spark gaps.

Steve.

How much 'boost' capacitance do you have (and what series resistor), normal practice (at least on the 1.6 Kw + stuff I am familiar with), you have a bank of 20,000uF or so in series with a few ohms across the power supply outputs just before the igniter. The idea is that this cap bank supplies the energy to heat the surface of the electrodes before the voltage collapses from 120V to the normal operating region of 20V or so.

Without this getting the lamp to strike reliably is hard, as the plasma will form then immediately collapse due to the cold electrodes having too high a work function.

If the silly thing is flashing over initially but the plasma is failing to stabilise, then I would suspect the boost supply rather then the igniter. That said short arc Xe igniters are IMHO black magic and I wouldn't rule anything out.

Ahh, but the whole igniter circuit is designed to be resonant, this is not a classical transformer! Think something more like a tesla coil (at least in the ones I have seen). Basically it is a high Q resonant circuit until the lamp ionises at which point it is damped by the low impedance of the lamp plasma.

I would think half that or less, but without actually seeing the circuit it is kind of difficult to know.

Regards, Dan (Sometime Cinema tech).

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I put together a trigger circuit for a xenon arc lamp back in 1972.

I used a mains-driven voltage multiplier to charge a stack of 1uF film capacitors up to about 2kV, where they discharged through a spark gap into a single-turn primary on a 24:1 step-up transformer, in which the secondary winding was the power lead to the lamp (12 turns of each lead).

I used a pair of big ferrite U-cores with a roughly 0.1mm air gap as my core.

The first prototype used a home-made spark gap between two steel spheres (1cm balls from a big ball-bearing) centred in a chunk of silica-glass tube.

I let the UV flash from this spark-gap illuminate the electrodes of the xenon arc lamp, and this arrangement triggered the arc lamp better than

90% of the time.

Later copies used a commercial spark-gap in a borosilicate glass envelope, and they triggered the arc closer to 10% of the time.

My theory was that the initial 40kV voltage spike had to coincide with the presence of a free electron between the electrodes of the arc lamp if it was going to initiate a discharge. With the prototype, the hard UV from the triggering spark-gap produced a photo-electron at the right time, and there was enough energy stored in the transformer inductance to sustain the discharge through the glow-discharge period until the electrode surfaces in the arc lamp had heated up enough to sustain an arc discharge - I found figures suggesting that only took about a microsecond.

Once the we had an arc, the regular power supply - a linear constant current source with a peak voltage output of about 40V DC - could sustain the discharge.

In the later copies, the transformer-capacitor circuit had to ring repeatedly until a cosmic ray or the like delivered an electron between the arc lamp electrodes to start the discharge, and by then, enough of the stored energy had been dissipated in the ringing that there was enough left over to carry the discharge through into the arc regime.

Sorting out what might be going on took quite a while - even with the

0.1mm gap, the ferrite core in the pulse trnasformer spent most of its time saturated, so the energy transfer from the primary to the secondary side must have taken a number of cycles before there was enough energy stored in the secondary side to generate the necessary break-down voltage across the arc lamp electrodes.

Once the gap had broken down, the core would not have been saturated and the primary and secondary sides would have been tightly coupled.

Back then, nobody made UV leds.

------- Bill Sloman, Nijmegen