Power Supply Design
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I am building a circuit that will be controlled by a Stamp II, but
powered by an LM2940 5 Volt Regulator (just like the one on the BOE).
Regarding the LM2940, it looks like I need to have a capacitor
between Vin and ground and another capacitor between Vout and
ground. Every book I look at, every article I read, every circuit I
see, has a different set of values for the capacitors. Even the BOE
uses a 1.0 uf tantalum cap between Vout and ground when the spec
sheet seems to indicate that... "The minimum output capacitance
required to maintain stability is 22 µF (this value may be increased
without limit). Larger values of output capacitance will give
improved transient response."
The Vin source will be a 9v transistor battery.
What values should I be using for the two capacitors? Do I need to
worry about using an aluminum electrolytic cap (for Vin and ground)
and a tantalum cap (for Vout and ground) given a relatively low
voltage source?
Thanks for hopefully clearing up a mystery!
powered by an LM2940 5 Volt Regulator (just like the one on the BOE).
Regarding the LM2940, it looks like I need to have a capacitor
between Vin and ground and another capacitor between Vout and
ground. Every book I look at, every article I read, every circuit I
see, has a different set of values for the capacitors. Even the BOE
uses a 1.0 uf tantalum cap between Vout and ground when the spec
sheet seems to indicate that... "The minimum output capacitance
required to maintain stability is 22 µF (this value may be increased
without limit). Larger values of output capacitance will give
improved transient response."
The Vin source will be a 9v transistor battery.
What values should I be using for the two capacitors? Do I need to
worry about using an aluminum electrolytic cap (for Vin and ground)
and a tantalum cap (for Vout and ground) given a relatively low
voltage source?
Thanks for hopefully clearing up a mystery!
Comments
regulators will sometimes go wacko and fail to regulate if you leave off the
caps. The regulator gets hot and you burn up whatever it is you are
powering.
Keep in mind most of the examples in the data sheets and so-forth are for
circuits powered off a DC power supply and not a battery. This could account
for the difference in capacitor values.
Original Message
I am building a circuit that will be controlled by a Stamp II, but
powered by an LM2940 5 Volt Regulator (just like the one on the BOE).
Regarding the LM2940, it looks like I need to have a capacitor
between Vin and ground and another capacitor between Vout and
ground. Every book I look at, every article I read, every circuit I
see, has a different set of values for the capacitors. Even the BOE
uses a 1.0 uf tantalum cap between Vout and ground when the spec
sheet seems to indicate that... "The minimum output capacitance
required to maintain stability is 22 µF (this value may be increased
without limit). Larger values of output capacitance will give
improved transient response."
The Vin source will be a 9v transistor battery.
What values should I be using for the two capacitors? Do I need to
worry about using an aluminum electrolytic cap (for Vin and ground)
and a tantalum cap (for Vout and ground) given a relatively low
voltage source?
Thanks for hopefully clearing up a mystery!
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--- In basicstamps@y..., Rodent <daweasel@s...> wrote:
> Whatever you do, don't run it without the caps. For some reason
those
> regulators will sometimes go wacko and fail to regulate if you
leave off the
> caps. The regulator gets hot and you burn up whatever it is you are
> powering.
>
> Keep in mind most of the examples in the data sheets and so-forth
are for
> circuits powered off a DC power supply and not a battery. This
could account
> for the difference in capacitor values.
>
>
Original Message
>
> I am building a circuit that will be controlled by a Stamp II, but
> powered by an LM2940 5 Volt Regulator (just like the one on the
BOE).
>
> Regarding the LM2940, it looks like I need to have a capacitor
> between Vin and ground and another capacitor between Vout and
> ground. Every book I look at, every article I read, every circuit I
> see, has a different set of values for the capacitors. Even the BOE
> uses a 1.0 uf tantalum cap between Vout and ground when the spec
> sheet seems to indicate that... "The minimum output capacitance
> required to maintain stability is 22 µF (this value may be increased
> without limit). Larger values of output capacitance will give
> improved transient response."
>
> The Vin source will be a 9v transistor battery.
>
> What values should I be using for the two capacitors? Do I need to
> worry about using an aluminum electrolytic cap (for Vin and ground)
> and a tantalum cap (for Vout and ground) given a relatively low
> voltage source?
>
> Thanks for hopefully clearing up a mystery!
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@y...
> 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/
Otherwise use the values off the data sheet.
Keep in mind you can't run much off a 9-volt battery anyway, so why not use
the Stamp regulator? Anything else that does not require a regulated source
can be run directly off the battery.
Original Message
Thanks for the insight! Any idea as to what values I should be using?
> Whatever you do, don't run it without the caps. For some reason
those
> regulators will sometimes go wacko and fail to regulate if you
leave off the
> caps. The regulator gets hot and you burn up whatever it is you are
> powering.
>
> Keep in mind most of the examples in the data sheets and so-forth
are for
> circuits powered off a DC power supply and not a battery. This
could account
> for the difference in capacitor values.
>
>
Original Message
>
> I am building a circuit that will be controlled by a Stamp II, but
> powered by an LM2940 5 Volt Regulator (just like the one on the
BOE).
>
> Regarding the LM2940, it looks like I need to have a capacitor
> between Vin and ground and another capacitor between Vout and
> ground. Every book I look at, every article I read, every circuit I
> see, has a different set of values for the capacitors. Even the BOE
> uses a 1.0 uf tantalum cap between Vout and ground when the spec
> sheet seems to indicate that... "The minimum output capacitance
> required to maintain stability is 22 µF (this value may be increased
> without limit). Larger values of output capacitance will give
> improved transient response."
>
> The Vin source will be a 9v transistor battery.
>
> What values should I be using for the two capacitors? Do I need to
> worry about using an aluminum electrolytic cap (for Vin and ground)
> and a tantalum cap (for Vout and ground) given a relatively low
> voltage source?