[ARC5] Cool New DC-DC Converter

[Scott Robinson]

Hi Brian

I get the idea that the primary switching process is shared first from 
long experience with such supplies, and second from the conceptual fact 
that regardless of how many outputs there are, the only source of power 
is the primary circuit.

The usual arrangement for AC line operated supplies is that the drive IC 
gets its power from two sources: first, a large resistor from the 
rectified line that charges a capacitor that runs the driver, and 
second, a diode from a separate transformer winding. If the output is 
shorted or overloaded, the transformer winding can't power the drive IC, 
and the supply shuts down, as the resistor won't carry the IC's load 
continuously. A 12V inout will be diferent, but for its own protection 
will need some power limiting means.

The rectifiers on any one output may not be able to do the trick I 
suggest, but detai study will figure that out.

Regards,

Scott


On 3/16/18 9:19 AM, Dennis Monticelli wrote:
> Brian,
> 
> I think there is a misunderstanding.  I think Scott was only trying to 
> point out that the primary winding and mag core are shared by all 
> secondary loads.  You can only get so many VA out of a transformer 
> before hitting the limitations of primary winding resistance and/or core 
> saturation.
> 
> Dennis AE6C
> 
> On Fri, Mar 16, 2018 at 2:42 AM, Brian <brianclarke01 at optusnet.com.au 
> <mailto:brianclarke01 at optusnet.com.au>> wrote:
> 
>     Hello Scott,
> 
>     Where did you get this idea that power supplies share their output
>     loads?
>     Doesn't apply to any SMPSU I know, nor to any rotary supplies either.
> 
>     73 de Brian, VK2GCE.
> 
>     On Friday, March 16, 2018 1:35 AM, Scott claimed:
>     Folks,
> 
>     Cold heaters take about twice as much as when warm. But, there's no
>     B+ drain then, so the supply can direct all its primary power
>     capability to the heater circuit. Most of these are power limited at
>     about 1.3 times the rating so:12V 3A is 36W + 60 mA x 520V = 25W
>     makes a total power limit of 61W. If all that is directed to a 12V
>     heater circuit, you could get 5A, or 10A for 6V. I'm not sure the
>     10A would actually work bu the 12V 5A ought to.
> 
>     Someone needs to buy one and see what it actually does.
> 
>     Happy glowing,
> 
>     Scott  Robinson
> 
> 
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