Ok to parallel LM2940''s ?
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Posts: 46,084
Randy,
That is what worried me. I don't have time to experiment with the idea laid
out below, although it seems like a good idea. Do you know of any regs that
can handle 2-4 amps? Low dropout if possible.
Thanks much for the idea and long post explaining it!
Jonathan
www.madlabs.info
Original Message
From: "Randy Jones" <randyjones@w...>
To: <basicstamps@yahoogroups.com>
Sent: Saturday, August 16, 2003 12:25 AM
Subject: Re: [noparse][[/noparse]basicstamps] Ok to parallel LM2940's ?
> Hi Jonathan,
>
> I don't recall ever seeing two of the 3-pin voltage regulator ICs
connected
> in parallel to increase the available output current. Just glanced
through
> the LM2940 data sheet, and didn't find any mention of doing this. Seems
> like the inevitable output voltage difference between the two might make
one
> "dominant" and cause unexpected effects. But I'm just guessing.
>
> Here is something that might be interesting to try... One could connect
> series diodes, such as 1N400x, to the output pins of each regulator - two
> regulators, two diodes. Connect the anode of each diode to one of the
> regulator output pins, and connect the two cathodes together for the
> combined output. Now there would be no possibility that current from one
> regulator could flow into the output pin of the other. But, but.... the
> output voltage is now dropped by one diode drop (and that voltage will
vary
> somewhat in relation to the current flowing through the diode).
>
> So... connect a series diode between each regulator ground pin and ground.
> The voltage drop through the series diode will bump up the voltage on the
> regulator's ground pin by one diode drop, causing the regulator's output
> voltage to increase by a like amount. Even with perfectly matched diodes
> the voltage drop through the output pin diodes would be greater than that
of
> the ground pin diodes, since there is (presumably) more current flowing
> through them . So you would lose some of the rather tight and accurate
> regulation from these nice regulators.
>
> Also, the LM2940 has a special output capacitor ESR value requirement to
> avoid possible oscillation, and I'm not sure if a connection like this
would
> make a problem more likely. I recently bought a capacitor ESR meter kit
> with the intent to study the performance of the LM2940 with capacitors of
> varying ESR. No results yet, though.
>
> Overall I think the above "idea" with the diodes is a bit "out there" and
> proves that I should be asleep right now! If you do try it, I would be
> interested in hearing about the results.
>
> There are circuits out there that use a power transistor connected to a
> 3-pin regulator so the regulator controls the voltage output and the power
> transistor handles the current to the load. As I recall, the transistor
in
> this application is called a "pass transistor." This might be a better
way
> to increase the current output vs. a single LM2940. I'm not sure if the
> LM2940 has any characteristics that would make it unsuitable for a "pass
> transistor" regulator circuit application.
>
> Okay... off to sleep now...
>
> Randy
>
>
>
Original Message
>
> From: "Jonathan Peakall" <jpeakall@m...>
> To: <basicstamps@yahoogroups.com>
> Sent: Friday, August 15, 2003 7:56 PM
> Subject: [noparse][[/noparse]basicstamps] Ok to parallel LM2940's ?
>
>
> > Hi All,
> >
> > Is it OK to parallel LM2940's for greater current output?
> >
> > Thanks,
> >
> > Jonathan
> >
> > www.madlabs.info
> >
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject
and
> Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
>
>
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>
>
That is what worried me. I don't have time to experiment with the idea laid
out below, although it seems like a good idea. Do you know of any regs that
can handle 2-4 amps? Low dropout if possible.
Thanks much for the idea and long post explaining it!
Jonathan
www.madlabs.info
Original Message
From: "Randy Jones" <randyjones@w...>
To: <basicstamps@yahoogroups.com>
Sent: Saturday, August 16, 2003 12:25 AM
Subject: Re: [noparse][[/noparse]basicstamps] Ok to parallel LM2940's ?
> Hi Jonathan,
>
> I don't recall ever seeing two of the 3-pin voltage regulator ICs
connected
> in parallel to increase the available output current. Just glanced
through
> the LM2940 data sheet, and didn't find any mention of doing this. Seems
> like the inevitable output voltage difference between the two might make
one
> "dominant" and cause unexpected effects. But I'm just guessing.
>
> Here is something that might be interesting to try... One could connect
> series diodes, such as 1N400x, to the output pins of each regulator - two
> regulators, two diodes. Connect the anode of each diode to one of the
> regulator output pins, and connect the two cathodes together for the
> combined output. Now there would be no possibility that current from one
> regulator could flow into the output pin of the other. But, but.... the
> output voltage is now dropped by one diode drop (and that voltage will
vary
> somewhat in relation to the current flowing through the diode).
>
> So... connect a series diode between each regulator ground pin and ground.
> The voltage drop through the series diode will bump up the voltage on the
> regulator's ground pin by one diode drop, causing the regulator's output
> voltage to increase by a like amount. Even with perfectly matched diodes
> the voltage drop through the output pin diodes would be greater than that
of
> the ground pin diodes, since there is (presumably) more current flowing
> through them . So you would lose some of the rather tight and accurate
> regulation from these nice regulators.
>
> Also, the LM2940 has a special output capacitor ESR value requirement to
> avoid possible oscillation, and I'm not sure if a connection like this
would
> make a problem more likely. I recently bought a capacitor ESR meter kit
> with the intent to study the performance of the LM2940 with capacitors of
> varying ESR. No results yet, though.
>
> Overall I think the above "idea" with the diodes is a bit "out there" and
> proves that I should be asleep right now! If you do try it, I would be
> interested in hearing about the results.
>
> There are circuits out there that use a power transistor connected to a
> 3-pin regulator so the regulator controls the voltage output and the power
> transistor handles the current to the load. As I recall, the transistor
in
> this application is called a "pass transistor." This might be a better
way
> to increase the current output vs. a single LM2940. I'm not sure if the
> LM2940 has any characteristics that would make it unsuitable for a "pass
> transistor" regulator circuit application.
>
> Okay... off to sleep now...
>
> Randy
>
>
>
Original Message
>
> From: "Jonathan Peakall" <jpeakall@m...>
> To: <basicstamps@yahoogroups.com>
> Sent: Friday, August 15, 2003 7:56 PM
> Subject: [noparse][[/noparse]basicstamps] Ok to parallel LM2940's ?
>
>
> > Hi All,
> >
> > Is it OK to parallel LM2940's for greater current output?
> >
> > Thanks,
> >
> > Jonathan
> >
> > www.madlabs.info
> >
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject
and
> Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>