dbc@tc.fluke.COM (Dan Carson) (11/07/89)
______ |7805| ~13Vdc | | 4.7Vdc | ------ | v | | | v _________ 120V AC ---- AC adapter ----------| | |-----------|26 ohms|------ V G V | --------- | i n o +-------|<-----------| n d u K A Gnd t As has been suggested, 10uF caps on the input and output of the 7805 might fix your problem. If that doesn't work, try a reverse-biased diode from the output of the 7805 to ground. I've had problems with various 3 terminal regulators latching off. It's usually caused by a glitch during power up which pulls the ouput below ground. The inductance of the relay coil might provide just such a glitch. Dan Carson John Fluke Mfg.
kline@tuna.cso.uiuc.edu (Charley Kline) (11/08/89)
In various articles, various people write:
about power supplies based on 78xx regulators.
I've been slapping together 5v power supplies for years with a fair amount
of success using the following. Anyone see any room for improvement without
driving up the cost? Yes I know I can use a 723 and 2N3055 power transistors
and do better, but that also would about double the cost of this.
Oh incidentally, THANKS!! to everyone who replied to my query about
replacement triacs for our dimmer packs. I ordered ten from Mouser to
get their quantity discount, and had to use one of them to replace a
triac that blew when an instrument shorted. It worked great. I'm
somewhat of a hero now because our little theatre is just about flat
broke and I saved a $80 service call to the local head band lighting
and sound joint. I tried to give credit to sci.electronics, but none of
the fine-arts types at the Station really comprehended what it is. :)
7805
+-----+ +-------+
<-----B|B---------|ac +|---+---------|in out|-------+------> +5
B|B | | | | gnd | |
120AC B|B T1 | B1 | =C1 +-------+ =C2
B|B | | | | |
<-----B|B---------|ac -|---+-------------+-----------+------> gnd
+-----+
T1 - 6.3v, 1.2A secondary power transformer.
B1 - 1.5A 100v bridge rectifier.
C1 - 2000uFd 16V electolytic
C2 - 47uFd 16V electolytic
_____
Charley Kline, ATD and gadgeteer, Celebration Company at the Station Theatre
c-kline@uiuc.edubrianr@phred.UUCP (Brian Reese) (11/10/89)
In article <1989Nov7.233936.24863@ux1.cso.uiuc.edu> kline@tuna.cso.uiuc.edu (Charley Kline) writes:
:>I've been slapping together 5v power supplies for years with a fair amount
:>of success using the following. Anyone see any room for improvement without
:>driving up the cost? Yes I know I can use a 723 and 2N3055 power transistors
:>and do better, but that also would about double the cost of this.
:>
:> 7805
:> +-----+ +-------+
:><-----B|B---------|ac +|---+---------|in out|-------+------> +5
:> B|B | | | | gnd | |
:>120AC B|B T1 | B1 | =C1 +-------+ =C2
:> B|B | | | | |
:><-----B|B---------|ac -|---+-------------+-----------+------> gnd
:> +-----+
:>
:>
:>T1 - 6.3v, 1.2A secondary power transformer.
:>B1 - 1.5A 100v bridge rectifier.
:>C1 - 2000uFd 16V electolytic
:>C2 - 47uFd 16V electolytic
Looks like a good GP supply. The only parts I would add to this would be
a reverse biased diode from the output to ground, and another from the
input to the output. Well, maybe a 0.1uF ceramic in parallel with C1 too.
Brian
--
Brian Reese uw-beaver!pilchuck!seahcx!phred!brianr
Physio Control Corp., Redmond, Wa. brianr@phred.UUCP
"Sticks and stones may break my bones, but whips and chains excite me!"
* Do not write on this line. This line has been left blank intentionally. *john@anasaz.UUCP (John Moore) (11/12/89)
In article <12236@fluke.COM> dbc@tc.fluke.COM (Dan Carson) writes:
]
] ______
] |7805|
] ~13Vdc | | 4.7Vdc
] | ------ |
] v | | | v _________
]120V AC ---- AC adapter ----------| | |-----------|26 ohms|------
] V G V | --------- |
] i n o +-------|<-----------|
] n d u K A Gnd
] t
]
]As has been suggested, 10uF caps on the input and output of the 7805 might
]fix your problem. If that doesn't work, try a reverse-biased diode from
You may find that putting the cap on the output will cause an oscillation.
The regulator really likes to see a resistive load, and a large capacitor
on the output makes it very reactive. I have had them oscillate with
10uf on the output, but work fine when that was cut to .1uF.
--
John Moore (NJ7E) mcdphx!anasaz!john asuvax!anasaz!john
(602) 861-7607 (day or eve) long palladium, short petroleum
7525 Clearwater Pkwy, Scottsdale, AZ 85253
The 2nd amendment is about military weapons, NOT JUST hunting weapons!