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Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
Here's the scenario for which I seek friendly advice: A HV power supply periodically discharges through a spark gap at 1,400vdc at around 1Hz. I plan to use a 20:1 TX to step down the high voltage pulses to low voltage pulses of about 70vdc. I'll use a TX, rather than a buck configuration, for isolation. Question is.... at such a low frequency (1Hz +/-) what type TX is a good candidate? Flyback, pulse, toroid, other?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
this is a high frequency problem rather than a low frequency one, the spark period and waveshape are of key interest. I think that Iron or even MnZn ferrites will be unsuitable, air or Ni-Zn ferrites are probably required. Although 1400V is not particularly high, isolation (capacitive coupling) will be challenging due to the very high dv/dt expected. I think I'd try a capacitively-coupled magnetic pulse transformer approach, good detail during the event with 1 second for d.c. recovery.
Alternatively you could use a (high frequency) voltage divider with amplifier/buffer, isolated power supply (dc:dc converter) and a high speed linear opto-
coupler. _________________________________________
__ EDIT: on re-reading it seems that you are not trying to monitor the voltage but to use it ? If so then a pulse transformer seems a good choice. The size of the transformer will be largely determined by current (= wire diameter) and integral(voltage.time) (= #turns.core area) during the spark, but extra space will be required for pri:sec isolation. Do you know the spark duration or energy ? What type of spark gap are you using? ================================== Most importantly, what is the power supply, and load ? ==================================
Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
The speak gap is an iridium tipped spark plug in proximity to a neodymium magnet for quenching. I've yet to measure the spark duration and energy, but needs to be done. The load is (2) 330,000uf caps in parallel.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
If your construction techniques are poor then your plan will work ... poorly. If your construction technique is good then you should prepare for an explosion :)
In effect you are going to connect a charged capacitor (your power supply) to a not-charged capacitor (via a transformer) Good construction technique would mean short thick wires/interconnects with little stray inductance (or transformer leakage inductance) so the very low inductance of wiring + components is all that limits the peak current. If your construction technique is poor then stray and leakage inductance, plus wiring resistances, will limit the current peak.
Or you could design-in some inductance (or transformer leakage inductance)
Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
Thanks Sulaiman, I'll try a capacitively-coupled magnetic pulse TX and also an old-style flyback TX observing good construction techniques all around. If either show notable results, I'll let you know.
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