DIY Blue Beam Dye Laser

[millirad]

I just harvested a flyback transformer from an RCA television. It is a DC transformer, rated for 26.9KV. Not sure about which circuit I'll use to create the nitrogen laser yet.

 

[HIMNL9]

As DC transformer, you mean a DC-DC converter, that include the oscillator ?

Cause usual flyback transformers for TV, needs an oscillator circuit, for work.

 

[millirad]

The oscillator circuit will need to be built which will drive the DC-DC LOPT/flyback transformer. I have read that the repetition rate on the laser firing must not be higher than 100HZ, and the flyback transformer does not like to be operated at less than ~15KHZ. So what is the solution? ;-/

 

[3zuli]

I think it's max 100Hz of AC, but the new flybacks usually have an internal diode, so it's putting out DC

 

[Benm]

The oscillator circuit will need to be built which will drive the DC-DC LOPT/flyback transformer. I have read that the repetition rate on the laser firing must not be higher than 100HZ, and the flyback transformer does not like to be operated at less than ~15KHZ. So what is the solution? ;-/

The 'typical' solution would be to have the flyback charge a capacitor, and dump all that charge into the laser at a certain voltage/charge level. This is how these nitrogen lasers are typically built, with the laser cavity and plates around is to serve as capacitor, and a spark gap that triggers at a certain charge level.

The repetition rate is determined by how much charging current the flyback provides, the capacity of the plates, and the trigger voltage for the sprak gap. By adjusting the spark gap, you can go from weak rapid pulses to stronger but slower ones.

As for the flyback itself: it requires an oscillator to operate it from a dc power source. Such circuits are available online, and probably not very difficult to build. The high voltage end of it is pretty dangerous though - its in the order of tens of kV, with several (dozen) watts of drive power behind it. Once you start buffering this output in capacitors it may very well amount to enough charge to zap you dead, so be careful!

 

[HIMNL9]

There was a solution (still searching between my files) for use the interior of am old "energy saving" lamp for drive a flyback transformer (not too much efficent nor "elegant", but at least works), but it's not too much safe, cause involve a direct connection with the main power.

Otherwise, you can use a self-triggered oscillator, but the configuration depend from the flyback that you have, i mean from the primary coils that already are on the transformer, and you need the datasheet of the transformer, for calculate the better configuration.

If you can re-wire the primary (not in the "new type" ones, glued in epoxy bath, but the "old types" with the primary and secondary winding made in 2 separate blocks can permit you to rewind the primary), you can use this old schematic ..... primary winding are 5 + 5 turns for the power section, connected to transistor collectors, and 2 + 2 turns for the reaction section (sorry for the bad schematics, i just drawed them now on-the-fly)

If you have one of those "all-dipped-in-resin" units, and no datasheets, you can try to use it the same ..... build the following circuit, use an amperometer on the positive wire (the one that power the circuit, not the positive of the flyback winding), and attach a pair of pieces of cable with two "crocodiles" clips in place of the primary of the flyback ..... set the oscillator around 15 KHz, then try the different coils of the primary section, checking the one that give you the better result (the better ark at the output, if you prefer ), but keep the current around 1 ampere or few more (if you see like 3 or 4 ampere, isn't the right coil) ..... when you have found the correct one, you can solder directly the wires to the flyback transformer

 

[millirad]

I see that Jarrod Kinsey's Neon sign transformer is running at 60HZ without any driver circuitry, which can not be done with the flyback transformer. So running the flyback at 15KHZ does not mean that the laser will fire at 15KHZ. The flyback will charge the plates/capacitors in the laser cavity and the spark gap, coil and spacing of the electrodes will determine its firing/repetition rate. This is somewhat different due to the differences in transformers, while operating similarly at the laser cavity.

 

[HIMNL9]

^ No, the 15 KHz thing (15625 Hz, to be precise), is just the frequency for which these TV flyback transformers are optimized ..... then you just feed the assembly with the DC current that come out from it, and the resonance of the assembly and spark gap decides the frequency at what the cavity works.

That assembly use the transformer just for power up the system, not for set up the frequency, you're right.

 

[millirad]

Will the 15.625 KHz be present in the resonant cavity, even though the spark gap setting will determine firing repetition rate of about 150~200 HZ ? And if this frequency is across the laser electrodes is it effecting the laser discharge at all ? BTW, I appreciate your help +1 rep.

 

[HIMNL9]

No, wait ..... the 15 KHz is the frequency that you use for drive the flyback transformer, is right, but the high voltage at the output is DC, cause almost all the flyback transformers, now, integrates a HV diode, and, the new ones, also the pump elevator (the diode/capacitor tripler network, i mean ..... the all-in-resin units usually have it already in the resin with the secondary coil).

So, the HV at the output is already DC, not AC ..... so, no 15 KHz in the cavity circuit, only the frequency that you set with the C-L-C bridge and the spark gap

 

[Benm]

The 15 kHz will not be present there, its rectified by the flybacks builtin diode, and buffered by the capacity of the plates and/or an external capacitor.

When using the neon sign transformer, no rectification is applied, and the laser just fires on every mains cycle... or rather twice, once on the low end and once on the high end, resulting in 100/120 Hz repetition depending on where you live.

 

[brtaman]

^ No, the 15 KHz thing (15625 Hz, to be precise), is just the frequency for which these TV flyback transformers are optimized ..... then you just feed the assembly with the DC current that come out from it, and the resonance of the assembly and spark gap decides the frequency at what the cavity works.

That assembly use the transformer just for power up the system, not for set up the frequency, you're right.

It really depends on the specific Flyback, assume you found a datasheet, with such a precise frequency?

Like Benm said, a capacitor with spark gap, will be what is used to control the number of bangs per second. The frequency of the flyback will not have much effect on operation. I built a TEA laser a long while ago, using the mediocre 2n3055 driver worked pretty decently, but I really cannot count the amount of things wrong with that driver. -.-

I really do suggest you go with the ZVS driver for the flyback, it is practically bullet proof when set-up. I think I am going to have a go at it myself once I finish my sstc.

 

[millirad]

Thanks for the info! I now realize that this potted flyback is the new style with integrated diode circuit. So I'm comfortable building the nitrogen laser now that I know there is HV DC coming from the output. With the addition of coumarin dye and some nitrogen gas the blue beam dye laser may come later if I get the laser cavity to work. I'm tempted to go with ZVS, the only concern is that one author mentions the negative lead of the flyback getting red hot. If there is a way to drop the power somewhat with the ZVS, I would be more comfortable using that design. And the ZVS is very lethal, while the lower power designs are possibly lethal if you make a mistake.

 

[HIMNL9]

Uh, if you're not used to work with high voltages, i suggest you to start to experiment with battery operated units at low currents, just for prevent accidents.

High voltages at low power can be very uncomfortables, but at high power, can be lethal

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Side note: definition of "accident" related to high voltages: "when you're playing with high voltages, if you start to feel all the hairs on your body rise up straight and start to spark at the extremities, look a blue/violet halo around your body, and start to smell "fried chicken" like, you probably had an accident" (J/K )

 

[millirad]

I am used to working in HV in general. But I think will use this circuit to drive the laser cavity............

 

[HIMNL9]

LOL, this look like my old 555 pwm schematic, with a totem-pole addon (the 2 transistors) ..... but yes, can work the same ..... just keep an eye on the currents, and use a good fuse on the power part (if the mos go shorted, you fry the transformer), and add a diode, 1N4007, or also better BY255, in parallel to the primary coil (cathode to +V), just in case you have to use a mos that don't have a built-in one (anyway, one more protection is always better than one less )