Multiple Regulators Question.

[Mike C.]

What kind of problems am I asking for by this setup?

I have regulated input power of 24VDC at 1amp.

The 24VDC is dropped down to 12VDC using a linear (7812) to run one
device (200mA). The Linear has a large Heatsink.

The 12VDC gets dropped again using a switch (LM2674) to 5VDC to run
another device (100mA).

The 5VDC gets dropped again with another Linear to 3.3VDC to run an
MPU (75mA). This Linear has no Heatsink.


Am I asking for trouble doing this?
If so, what can happen?

Mike C.

 

[Baphomet]

"Mike C." <noemail@nospam.com> wrote in message
news:i2m4pvc98srol3jekevfk91h29af6ob4ca@4ax.com...

What kind of problems am I asking for by this setup?

I have regulated input power of 24VDC at 1amp.

The 24VDC is dropped down to 12VDC using a linear (7812) to run one
device (200mA). The Linear has a large Heatsink.

The 12VDC gets dropped again using a switch (LM2674) to 5VDC to run
another device (100mA).

The 5VDC gets dropped again with another Linear to 3.3VDC to run an
MPU (75mA). This Linear has no Heatsink.


Am I asking for trouble doing this?
If so, what can happen?

From a quickie look at some of the specs., it looks like everything is well
within dissipative limits. If so, the question then becomes one of
reliability. If the first regulator fails in the open mode, you will lose
all of your voltages but then again, maybe that is precisely what you want.
It's hard to tell from the way you posted the question.

 

[SHAUN]

"Mike C." <noemail@nospam.com> wrote in message
news:i2m4pvc98srol3jekevfk91h29af6ob4ca@4ax.com...

What kind of problems am I asking for by this setup?

I have regulated input power of 24VDC at 1amp.

The 24VDC is dropped down to 12VDC using a linear (7812) to run one
device (200mA). The Linear has a large Heatsink.

The 12VDC gets dropped again using a switch (LM2674) to 5VDC to run
another device (100mA).

The 5VDC gets dropped again with another Linear to 3.3VDC to run an
MPU (75mA). This Linear has no Heatsink.


Am I asking for trouble doing this?
If so, what can happen?

Mike C.

Mike what devices are these source voltages running and how many amps are
they pulling?

 

[SHAUN]

"Baphomet" <fandaDEATH2SPAMMERS@catskill.net> wrote in message
news:vp50iui93fke51@corp.supernews.com...

"Mike C." <noemail@nospam.com> wrote in message
news:i2m4pvc98srol3jekevfk91h29af6ob4ca@4ax.com...
What kind of problems am I asking for by this setup?

I have regulated input power of 24VDC at 1amp.

The 24VDC is dropped down to 12VDC using a linear (7812) to run one
device (200mA). The Linear has a large Heatsink.

The 12VDC gets dropped again using a switch (LM2674) to 5VDC to run
another device (100mA).

The 5VDC gets dropped again with another Linear to 3.3VDC to run an
MPU (75mA). This Linear has no Heatsink.


Am I asking for trouble doing this?
If so, what can happen?

From a quickie look at some of the specs., it looks like everything is
well
within dissipative limits. If so, the question then becomes one of
reliability. If the first regulator fails in the open mode, you will lose
all of your voltages but then again, maybe that is precisely what you
want.
It's hard to tell from the way you posted the question.

That's what I was thinking also Baph??

 

[Mike C.]

On Sun, 19 Oct 2003 08:22:21 -0700, "Baphomet"
<fandaDEATH2SPAMMERS@catskill.net> wrote:

"Mike C." <noemail@nospam.com> wrote in message
news:i2m4pvc98srol3jekevfk91h29af6ob4ca@4ax.com...
What kind of problems am I asking for by this setup?

I have regulated input power of 24VDC at 1amp.

The 24VDC is dropped down to 12VDC using a linear (7812) to run one
device (200mA). The Linear has a large Heatsink.

The 12VDC gets dropped again using a switch (LM2674) to 5VDC to run
another device (100mA).

The 5VDC gets dropped again with another Linear to 3.3VDC to run an
MPU (75mA). This Linear has no Heatsink.


Am I asking for trouble doing this?
If so, what can happen?

From a quickie look at some of the specs., it looks like everything is well
within dissipative limits. If so, the question then becomes one of
reliability. If the first regulator fails in the open mode, you will lose
all of your voltages but then again, maybe that is precisely what you want.
It's hard to tell from the way you posted the question.

Thanks for answering..

As far as losing the 1st regulator open, I would want all other power
lost.

The 5VDC circuit has a crowbar circuit set at 5.6VDC. In a disaster
when the 1st regulator shorts and 24VDC is passed through, the crowbar
*should* protect the components on the 5VDC side. If the 5VDC to
3.3VDC circuit fails shorted, the MPU circuit also has over-volt
protection.

Mike C.

 

[CFoley1064]

What kind of problems am I asking for by this setup?

Perfectly acceptable, but make sure you have a good output cap (low ESR at
higher frequencies) for the 7812, and use a low dropout regulator for pulling
the 5V dowm to 3.3V -- you'll have bad regulation if you use an LM317, not
enough headroom.

Good luck.
Chris