[R-390] Re: R-390 Voltage Regulator

[Barry Hauser]

Hi Bob

The R-391 that turned up with the solid-stated regulator has no real heat 
sink to speak of, was modded long ago -- so probably run a long time.  It 
literally runs cold.  There was nothing particularly high tech -- couple of 
transistors -- small tab mounts, couple of zeners and a few other parts.

As I recall, there was a smudge of heat sink grease and a hole on one side 
of the 6082 shield where it looked like the modder tried to mount one of the 
transistors.  That tab mount is just sticking up on the perboard -- with 
some telltale heat sink grease on it.

This is not to argue -- just what was observed.  It was written up in HSN a 
couple of years ago.

I'm more than a bit rusty on the theory, but as I recall, when figuring the 
parameters for a VR circuit, it's has to do with the maximum portion of the 
power that's being dissipated by the VR -- not the total of the supply.  In 
other words, if the unregulated coming in is 200 vdc and the VR is set to 
maintain 180, it's dissipating 20 v X whatever ma's.  Something like that. 
If I'm not mistaken, the B+ fuse is the same as in an R-390A -- 1/8th amp, 
so a max of 125 ma?

But, I dunno about that ... but this VR runs cool with no heatsinking, not 
even mounted to the frame or module.  AC voltage runs high around here - 
126-127 v., and when I tested it, I ran it up to nearly 135 with the variac. 
The zeners in the circuit are also small, though I can't tell the wattage by 
just lookin'.


Barry

----- Original Message ----- 
From: "Bob Camp" <ham at cq.nu>
To: "R-390A Receiver List" <r-390 at mailman.qth.net>
Sent: Saturday, March 26, 2005 10:31 AM
Subject: Re: [R-390] Re: R-390 Voltage Regulator


> Hi
>
> If you are going to try the solid state R390 not an A regulator conversion 
> here's a starting point on the pass device.
>
> For a whopping $5.67 you can get a IRFPE30 from International Rectifier. 
> Data sheet is at 
> http://www.irf.com/product-info/datasheets/data/irfpe30.pdf.
>
> Into an infinite heat sink the part is rated at 125 watts at room 
> temperature. At 70C the part will handle 75 watts. Since we are running 20 
> to 30 watts that seems about right. The heat sink we attach it to probably 
> will need to be a bit better than a radio bulkhead, but still smaller than 
> the entire rest of the radio.
>
> With an 800 volt rating out to 2 amps overload and over voltage should not 
> be a major issue. It also has a built in reverse protection diode so 
> that's one less part you have to wire in.
>
> Looks like the only major issue is the power dissipation.
>
> Without a lot of work 30 watts seems like a reasonable starting point. The 
> MOSFET has a lot better saturation characteristics than the tube. That 
> means that we don't need quite as much headroom on the regulator. A simple 
> trick is to put a resistor in series with the transistor to soak up part 
> of the power. If half of the power is in the resistor that cuts our heat 
> sink down to the 15 watt region. With a fan on it that can be a fairly 
> small  chunk of metal. With no fan you will need a fairly large chunk of 
> extrusion. Without going to far on heat sink design the part should be 
> about 6 X 6 X 3 if it's a normal multi fin chunk of aluminum extrusion. 
> That will keep the temperature down to the point that you won't cause 
> burns if you bump into it. If you don't use the resistor trick then the 
> heat sink goes to about 10X4X3. That's a pretty big heat sink ...
>
> Bottom line is that the tubes run quite a bit hotter than the 
> semiconductors. That makes them easier in the heat removal department. For 
> the same margin in the design the volume of the semiconductor plus heat 
> sink will be at least as large or larger than the tubes it replaces.
>
> Still hanging on to my box of 6082's ....
>
> Take Care!
>
> Bob Camp
> KB8TQ
>
>
>
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