[Amps] Zero Crossing circuit

[wb8jkr at juno.com]

 I think the acquired advantage with the zero 
crossing is then there isn't a chance the power
supply will be turned on at the AC cycle peak.

Mark  WB8JKR


On Wed, 17 Nov 2004 20:03:55 -0500 jeff millar <wa1hco at adelphia.net>
writes:
> Ed...
> 
> I've used zero voltage switched solid state relays twice in 2KW 
> amplifiers, one at 432 and one at 144 MHz.  The 432 amp included the 
> 
> normal step start circuit, but once I noticed that the zero voltage 
> switching feature, I tried it without a step start in the 144 amp.  
> The 
> circuit switched on with very little drama, the lights blinked about 
> the 
> same amount as when transmitting at full power.
> 
> One design note on high voltage power supplies suggested that 
> extremely 
> high surge currents can damage electrolytic capacitors.  These surge 
> 
> current maximizes when the turn on relay or switch happens to make 
> contact at the peak of the line cycle.  The zero voltage switching 
> function reduces the surge currents to approximately the same amount 
> as 
> what it takes to recharge the caps at the peak of the line cycle. 
> 
> These amps showed no signs of RF getting into the switches, 
> including 
> during operation at a big hilltop VHF/UHF multi-multi contest  group 
> 
> with 1.5 KW on all the bands.  But for HF amps with a lot more RF 
> currents flowing around the shack, it's probably best to run the 
> control 
> leads through an EMI filter similar to what you find on a AC power 
> inlet.
> 
> One caution, the off impedance of these switches doesn't look that 
> good 
> in the spec sheet, leading to the conclusion that an "off" power 
> supply 
> could have 10 to 100's of volts on the output.  I didn't see this, 
> the 
> voltage didn't rise above a volt or so, but maybe unit to unit 
> variation 
> or operation at high temperature could cause more leakage.
> 
> hope this helps,
> 
> jeff, wa1hco
> 
> Ed Stallman <n5blz1 at houston.rr.com> writes:
> 
> >>Wondering if anyone has used a zero crossing circuit on a high 
> voltage
> >>supply to reduce inrush current at startup? would this work for 
> soft start
> >>or would it just assist?
> >>Ed N5BLZ
> >>
> >>
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