[Elecraft] Switching v. Linear Power Supplies

[Don Brown]

Hi

I have a MFJ-4245MV, a MFJ-4225MV and a MFJ-4125. I also have an Astron S=
S-25M =20

The 45 amp supply runs my shack and had no problem running a K2/100 at 10=
0 watts and a TenTec 6n2 2 meter with amp at 150 watts at the same time d=
uring field day. The 25 amp I use on my bench for radio testing and as a =
general purpose power supply. I am planning to build the 4125 into an EC2=
 case to match the K2

I have never had any hash or RF noise from any of these supplies. The mea=
sured ripple is around 20 MV PK to PK at 5 amps out on all of them. I wou=
ld guess it would be hard to find any switcher with ripple down to 5 MV. =
The MFJ supplies are rated at 35 MV ripple at full rated output. The MFJ =
supplies have an external voltage adjust, lighted meters, an internal fan=
 and a cigarette lighter socket on the front panel so you can charge a HT=
 or cell phone. The Astron has one power connector on the back, non light=
ed meters, an internal voltage adjust and an external fan on the back. An=
y of them will drive a K2/100 with no problems.

Don Brown
KDD5NDB
----- Original Message -----
From: Rick Lellinger
Sent: Tuesday, July 09, 2002 1:28 AM
To: elecraft@mailman.qth.net
Subject: [Elecraft] Switching v. Linear Power Supplies

Greetings,

I've been working with electronics as a hobbyist for over twenty years an=
d
I've always powered my projects with linear power supplies.  I no longer
have access to my heavy 30amp Astron supply and I'm considering an MFJ 13=
.8v
25amp (#4225) switching supply (reduced weight and size). It will power b=
oth
my K2 and a VHF radio. However, I am concerned about RF hash from the uni=
t
as well as ripple. I noticed that the MJF supply has a ripple figure of 3=
5mv
while a comparable Astron linear supply has a mere 5mv of ripple. The
voltage regulation is fine, which is good.

1. Has anyone used the MFJ 4225 switching supply with good results, that =
is
decent regulation and NO hash (Rx OR TX) ?

2. Is 35mv of ripple too high? I know that the K2 and most good radios
contain excellent voltage regulating circuitry and so this may not be an
issue.

Thanks

Rick L




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