78s40 regulator

E

exxos

Guest
Hi all,

I've built a nice little 78S40 regualtor which works fine, my first
questions is this seems to be a old IC according to some websites, though if
this is the case, whats the new versions number ? Can't even find it on
Motorolas site....

Second question is its limited to a 1-40VDC voltage (not the IC supply
voltage), which is understandable, but if its using this (assuming 40VDC DC
output) output voltage to regulate itself, then feeding in like 100VDC would
appear to blow the chip up since its only 40VDC rated, so if the feedback
voltage has a upper limited of 40VDC (like the datasheet says 1V-40VDC
output) then would it work to simply feed in say 80VDC and place a 40Vzener
to the feedback pin on the IC, the IC would see then 40VDC and regulate it,
but the actual output would be 80VDC, has anyone tried this type of thing ?

I thought id ask about this one since its my first PSU of this type, I'm
aware of risks and dangers before anyone gets uptight about it, I do mean
this since Ive spent the last 10 or so years repairing all kinda of PSU
units, though building one from scratch yourself tends to open up a few
more doors than one is used to ;)

Cheers,
Chris
 
"exxos" <exxos@home.co.uk> wrote in message
news:40d4cc78$0$278$cc9e4d1f@news-text.dial.pipex.com...
Hi all,

I've built a nice little 78S40 regualtor which works fine, my first
questions is this seems to be a old IC according to some websites, though
if
this is the case, whats the new versions number ? Can't even find it on
Motorolas site....

Second question is its limited to a 1-40VDC voltage (not the IC supply
voltage), which is understandable, but if its using this (assuming 40VDC
DC
output) output voltage to regulate itself, then feeding in like 100VDC
would
appear to blow the chip up since its only 40VDC rated, so if the feedback
voltage has a upper limited of 40VDC (like the datasheet says 1V-40VDC
output) then would it work to simply feed in say 80VDC and place a
40Vzener
to the feedback pin on the IC, the IC would see then 40VDC and regulate
it,
but the actual output would be 80VDC, has anyone tried this type of thing
?

I thought id ask about this one since its my first PSU of this type, I'm
aware of risks and dangers before anyone gets uptight about it, I do mean
this since Ive spent the last 10 or so years repairing all kinda of PSU
units, though building one from scratch yourself tends to open up a few
more doors than one is used to ;)

Cheers,
Chris
Click to expand...
http://www.google.com/search?hl=en&ie=UTF-8&q=78S40

produced at least three different PDF data sheets in the first two pages of
hits.
 
"Norm Dresner" <ndrez@att.net> wrote in message
news:zn8Bc.7534$OB3.2157@bgtnsc05-news.ops.worldnet.att.net...
"exxos" <exxos@home.co.uk> wrote in message
news:40d4cc78$0$278$cc9e4d1f@news-text.dial.pipex.com...
Hi all,

I've built a nice little 78S40 regualtor which works fine, my first
questions is this seems to be a old IC according to some websites,
though
if
this is the case, whats the new versions number ? Can't even find it on
Motorolas site....

Second question is its limited to a 1-40VDC voltage (not the IC supply
voltage), which is understandable, but if its using this (assuming 40VDC
DC
output) output voltage to regulate itself, then feeding in like 100VDC
would
appear to blow the chip up since its only 40VDC rated, so if the
feedback
voltage has a upper limited of 40VDC (like the datasheet says 1V-40VDC
output) then would it work to simply feed in say 80VDC and place a
40Vzener
to the feedback pin on the IC, the IC would see then 40VDC and regulate
it,
but the actual output would be 80VDC, has anyone tried this type of
thing
?

I thought id ask about this one since its my first PSU of this type, I'm
aware of risks and dangers before anyone gets uptight about it, I do
mean
this since Ive spent the last 10 or so years repairing all kinda of PSU
units, though building one from scratch yourself tends to open up a few
more doors than one is used to ;)

Cheers,
Chris


http://www.google.com/search?hl=en&ie=UTF-8&q=78S40

produced at least three different PDF data sheets in the first two pages
of
hits.
Click to expand...

this is how I kinda built the circuit in the first place...

Chris
 
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