[Amps] Using switch mode power supply for heater power

[Dr. David Kirkby]

On 06/28/11 05:54 PM, Radio WC6W wrote:
> Hi David,
>    Been there, done that.
>
> http://qsl.net/wc6w/wc6wamps/index.html?fr63.html

Thank you. Though that needs another psu - I know one will probably be 
available, but it would be nice to make the heater supply self-contained.

>    Though the amp didn't end up small nor lite!
>
> http://web.archive.org/web/20010825210138/http://www.angenent.org/W7IUV/wc6w/wc6w_1.htm
>
>    The switcher may be just be glimpsed under the Pi coil in the photo on the left side at the bottom of the page.
>
>    What about an SPS for the plate supply?  Far greater potential/size weight savings there!

Very true, but there are two things to consider.
1) The voltage does not need to be stabilised.

2) HV switch mode power supplies are not common, and hence are expensive. If 
anyone knows a source of them able to provide 3 kV at 900 mA or more, let me 
know. But these are very much professional devices and unless one is extramly 
lucky, one is highly unlikely to get one at a sensible price.

dave



> 73&  Good morning,
>    Marv WC6W
>
> http://qsl.net/wc6w/
>
>
> --- On Tue, 6/28/11, Dr. David Kirkby<david.kirkby at onetel.net>  wrote:
>
>> From: Dr. David Kirkby<david.kirkby at onetel.net>
>> Subject: [Amps] Using switch mode power supply for heater power
>> To: "'AMPS'"<amps at contesting.com>
>> Date: Tuesday, June 28, 2011, 5:57 AM
>> 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?
>> --
>> A: Because it messes up the order in which people normally
>> read text.
>> Q: Why is top-posting such a bad thing?
>> A: Top-posting.
>> Q: What is the most annoying thing in e-mail?
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>


-- 
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?