[Amps] Using switch mode power supply for heater power

[Hsu]

1) the PS should be soft start
 2) Give more attention on  insulation between primary .and secondary of  SMPS transisformer, at least
  10000V, if use in 4CX10000A. 
 3) Give more attention  on  receiver 's niose( EMI problem)
----- Original Message ----- 
From: "Dr. David Kirkby" <david.kirkby at onetel.net>
To: "'AMPS'" <amps at contesting.com>
Sent: Tuesday, June 28, 2011 8:57 PM
Subject: [Amps] Using switch mode power supply for heater power


> I'm looking at building a 4CX1000A amp, which I want to make as small/light as 
> practical. Using an SMPS for the heater would go some way to this, whilst 
> offering regulation, since my own supply varies by more than +/-5% and a 
> generator would vary even more.
> 
> The 4CX1000A needs 6.0 V at 9 A, but of course when cold it will be a very low 
> resistance. I thought of using a 7.5 V 13.5 A switch-mode supply, with a 0.17 
> Ohm series resistor to drop 1.5 V. But I'm concerned the heater will never get 
> hot, as the cold resistance of the tube will draw too much current, causing the 
> SMPS to shut down.
> 
> If I bought one rated 12 V at 18 A or more, then dropping 6 V across a 0.67 Ohm 
> series resistor would mean the current would never exceed 18 A, even if the 
> heater is a dead short when cold. But that's a lot of wasted power, and an 
> over-specified (i.e. expensive, heavy) power supply.
> 
> Another option might be a NTC inrush current limiter. I've not looked at what's 
> available, but I do know device exist for this sort of task.
> 
> Does anyone have any ideas on the best way to use an SMPS for a heater supply?
> -- 
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