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RS 22-507 Power Supply

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Augie "Gus" Hansen

RS 22-507 Power Supply

I have been using a Radio Shack switching power supply (part number RS
22-507), which is a 13.8 volt, 3 amp supply both to power my K2 and to
power a test setup for a microcontroller project. The output is clean
and stable when the unit is powered on.

However, the supply is exhibiting a strange behavior when the unit is
turned off. It puts out a short full-voltage pulse (~0.2 second) at
intervals of several minutes. These pulses occur whether the supply is
connected to a load or not. It is not related to anything on the AC
input side. The same behavior was seen at a temporary lab I set up in
Rhode Island and here in my lab in Denver.

I wonder if any of you have had a similar experience with this model or
any other switching supply. If so, please let me know.

73,
Gus Hansen
KB0YH

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n6wg

Re: RS 22-507 Power Supply

Gus
I remember reading somewhere that switching supplies
require some minimum load to be stable. You could
try putting a small resistive load, maybe 50 mA, on the
P/S and see if it calms down.
Good luck and 73
Bob N6WG

----- Original Message -----
From: "Augie Hansen" <[hidden email]>
To: "Elecraft Reflector" <[hidden email]>
Sent: Tuesday, March 27, 2007 9:04 AM
Subject: [Elecraft] RS 22-507 Power Supply

> I have been using a Radio Shack switching power supply (part number RS
> 22-507), which is a 13.8 volt, 3 amp supply both to power my K2 and to
> power a test setup for a microcontroller project. The output is clean
> and stable when the unit is powered on.
>
> However, the supply is exhibiting a strange behavior when the unit is
> turned off. It puts out a short full-voltage pulse (~0.2 second) at
> intervals of several minutes. These pulses occur whether the supply is
> connected to a load or not. It is not related to anything on the AC
> input side. The same behavior was seen at a temporary lab I set up in
> Rhode Island and here in my lab in Denver.
>
> I wonder if any of you have had a similar experience with this model or
> any other switching supply. If so, please let me know.
>
> 73,
> Gus Hansen
> KB0YH
>
> _______________________________________________
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Augie "Gus" Hansen

Re: RS 22-507 Power Supply

Bob Tellefsen wrote:
> Gus
> I remember reading somewhere that switching supplies
> require some minimum load to be stable. You could
> try putting a small resistive load, maybe 50 mA, on the
> P/S and see if it calms down.
> Good luck and 73
> Bob N6WG

Hi Bob,

The loads on the supply are greater than 200mA in each of the operating
cases I described. My concern is not with output stability under load.
Rather, I want the supply to really be off when I turn off its power
switch. It apparently isn't, producing those unexpected pulses.

I was alerted to this problem when my computer kept displaying messages
about a network connection being connected and disconnected
periodically. The PIC MCU project I'm working on has a Lantronix XPort
IP-to-serial interface unit on it, and the short bursts of power were
causing it to wake up and respond over the network.

Thanks,
Gus

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David Cutter

Re: RS 22-507 Power Supply

It sounds like a malfunction in the start-up circuit. How is the psu
switched off? My guess is it is not an isolating switch on the supply
input, but some low power circuit that sends a signal to the start-up
circuit. This is not an area to be tackled lightly, as it is at mains
potential. Over here that can be lethal, but still be careful how you
investigate.

David
G3UNA

----- Original Message -----
From: "Augie Hansen" <[hidden email]>
To: "Bob Tellefsen" <[hidden email]>
Cc: "Elecraft Reflector" <[hidden email]>
Sent: Tuesday, March 27, 2007 10:06 PM
Subject: Re: [Elecraft] RS 22-507 Power Supply

> Bob Tellefsen wrote:
>> Gus
>> I remember reading somewhere that switching supplies
>> require some minimum load to be stable. You could
>> try putting a small resistive load, maybe 50 mA, on the
>> P/S and see if it calms down.
>> Good luck and 73
>> Bob N6WG
>
> Hi Bob,
>
> The loads on the supply are greater than 200mA in each of the operating
> cases I described. My concern is not with output stability under load.
> Rather, I want the supply to really be off when I turn off its power
> switch. It apparently isn't, producing those unexpected pulses.
>
> I was alerted to this problem when my computer kept displaying messages
> about a network connection being connected and disconnected periodically.
> The PIC MCU project I'm working on has a Lantronix XPort IP-to-serial
> interface unit on it, and the short bursts of power were causing it to
> wake up and respond over the network.
>
> Thanks,
> Gus
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Elecraft web page: http://www.elecraft.com

Augie "Gus" Hansen

Re: RS 22-507 Power Supply

David Cutter wrote:
> It sounds like a malfunction in the start-up circuit. How is the psu
> switched off? My guess is it is not an isolating switch on the
> supply input, but some low power circuit that sends a signal to the
> start-up circuit. This is not an area to be tackled lightly, as it is
> at mains potential. Over here that can be lethal, but still be
> careful how you investigate.

Thanks for the advice, David.

I'll trace out the circuit when I finish my current project (time is
tight right now) and do some troubleshooting. Having learned electronics
as a kid back in the tube/valve era (radio and TV broadcast in the late
1950s and 1960s), I tend to be wary around AC and high-voltage circuits.
I worked as a transmitter engineer one summer between semesters at
WEAN/WPJB-FM in Providence, RI. The chief engineer impressed the
importance of caution around such circuits by showing me a picture of a
"fried" engineer who had gotten across the HV in the 5KW AM walk-in
transmitter at the site several years earlier. That made a lasting
impression on me for sure.

Cheers,
Gus Hansen
KB0YH

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