voltage regulators - in parallel?

A

anonymous

Guest
can multiple voltage regulators be run in parallel? Each terminating in a
separate output? IE - the inputs are tied together but the outputs are
separated.

I put together a small board hoping to break an 18V 400mA wall wart into 4
9V sections. Im getting some wierd output (8V at the Vout for the
regulators) thats making me wonder whether my concept is fundamentally
flawed.
 
Subject: voltage regulators - in parallel?
From: "anonymous" anonymous@catfarm.com
Date: 10/9/2004 3:48 PM Central Daylight Time
Message-id: <%8Y9d.362926$Fg5.99330@attbi_s53

can multiple voltage regulators be run in parallel? Each terminating in a
separate output? IE - the inputs are tied together but the outputs are
separated.

I put together a small board hoping to break an 18V 400mA wall wart into 4
9V sections. Im getting some wierd output (8V at the Vout for the
regulators) thats making me wonder whether my concept is fundamentally
flawed.
Click to expand...
You might first check how much current you're using. Too much, and you might
be bogging dowm the wall wart. If not, there's no problem with using the 18V
to make multiple 9V supplies, as long as you don't connect their outputs
together (double-check your wiring here). (see other post for more
information).

Good luck
Chris
 
You might first check how much current you're using. Too much, and you
might
be bogging dowm the wall wart. If not, there's no problem with using the
18V
to make multiple 9V supplies, as long as you don't connect their outputs
together (double-check your wiring here). (see other post for more
information).

Good luck
Chris
Click to expand...
So what would be causing the Vout to drop to 8V? its consistent across all 4
regulators.
 
So what would be causing the Vout to drop to 8V? its consistent across
all 4 regulators.
Click to expand...
Operator error?



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anonymous wrote:
You might first check how much current you're using. Too much, and you
might
be bogging dowm the wall wart. If not, there's no problem with using the
18V
to make multiple 9V supplies, as long as you don't connect their outputs
together (double-check your wiring here). (see other post for more
information).

Good luck
Chris



So what would be causing the Vout to drop to 8V? its consistent across all 4
regulators.
Click to expand...
How much current are you drawing from the four outputs? As Chris said,
if you are drawing too much current the wall wart output voltage will drop.

Can you measure the voltage at the input to the regulators? It will
need to be >12V (approx. depends on the regulator) for your regulators
to operate correctly.

Gareth.

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To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris
 
anonymous wrote:

So what would be causing the Vout to drop to 8V? its consistent across all 4
regulators.
Click to expand...
What does the input voltage drop to when the output voltage is 8?

--
John Popelish
 
anonymous wrote:
Yes, you can connect 4 inputs of 4 regulators to the same source,
if the regulators have different loads. But the total load
current of all 4 outputs can not exceed 400mA before the
input will start dropping.

How much is the load current for each output?

-Bill


For the test I ran I was drawing ~5mA. But I read 8V at the regulators when
there is no load at all.
Click to expand...
Maybe its time for a new battery in that multimeter?

A good test would be to check the voltage across a 9v battery with the
same meter.

The other possibility is that your regulators are either bad, or they
are oscillating. Put a small load on them, and also use a 0.01uF (10nF)
cap across the output.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
Yes, you can connect 4 inputs of 4 regulators to the same source,
if the regulators have different loads. But the total load
current of all 4 outputs can not exceed 400mA before the
input will start dropping.

How much is the load current for each output?

-Bill
Click to expand...
For the test I ran I was drawing ~5mA. But I read 8V at the regulators when
there is no load at all.
 
"anonymous" <anonymous@catfarm.com> wrote in message news:<%8Y9d.362926$Fg5.99330@attbi_s53>...
can multiple voltage regulators be run in parallel? Each terminating in a
separate output? IE - the inputs are tied together but the outputs are
separated.

I put together a small board hoping to break an 18V 400mA wall wart into 4
9V sections. Im getting some wierd output (8V at the Vout for the
regulators) thats making me wonder whether my concept is fundamentally
flawed.
Click to expand...
Yes, you can connect 4 inputs of 4 regulators to the same source,
if the regulators have different loads. But the total load
current of all 4 outputs can not exceed 400mA before the
input will start dropping.

How much is the load current for each output?

-Bill
 
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