AAA battery substitute power supply circuit design info?

[fuspam]

Hi,

I'd like to build a circuit that will allow me to power
a single AAA battery-driven electronic device, but do
it by modifying DC coming from a typical wall wart
AC adapter (like one of those itty-bitty ones for
recharging cell phone batteries: outputs 3.7VDC @ 0.35A).
Unfortunately, the device (a portable MP3 player) doesn't
have a jack for DC input coming from an AC adapter.

Could somebody refer me to a resource or reference
(online or otherwise) that contains diagrams for
building a such a thing? I'm handy with electronics,
know how to solder, can read a diagram, have lots of
parts lying around... what I don't have is the know-how
to build a circuit that will supply the correct
voltage/amperage to sub for a AAA battery, that won't
blow up my device. My Google searches have not
borne any fruit as yet.

Thanks in advance,

JT

 

[CFoley1064]

Hi,

I'd like to build a circuit that will allow me to power
a single AAA battery-driven electronic device, but do
it by modifying DC coming from a typical wall wart
AC adapter (like one of those itty-bitty ones for
recharging cell phone batteries: outputs 3.7VDC @ 0.35A).
Unfortunately, the device (a portable MP3 player) doesn't
have a jack for DC input coming from an AC adapter.

Could somebody refer me to a resource or reference
(online or otherwise) that contains diagrams for
building a such a thing? I'm handy with electronics,
know how to solder, can read a diagram, have lots of
parts lying around... what I don't have is the know-how
to build a circuit that will supply the correct
voltage/amperage to sub for a AAA battery, that won't
blow up my device. My Google searches have not
borne any fruit as yet.

Thanks in advance,

JT

The simplest thing you could do is buy a
Cat #273-1662 1.5-12VDC/300mA Regulated AC-to-DC Adapter from Radio Shack.
That'll give you a regulated 1.5 VDC, and you can do the rest. Set the RS
adapter for 1.5VDC. If there isn't a DC power jack built in (if there is, just
buy an Adaptaplug(r) from the same source), find out where the + and - are on
the circuit board, and just solder the wires right on. Use a strain relief to
keep from pulling on the solder joints.

Good luck.
Chris

 

[Watson A.Name - Watt Sun]

Hi,

I'd like to build a circuit that will allow me to power
a single AAA battery-driven electronic device, but do
it by modifying DC coming from a typical wall wart
AC adapter (like one of those itty-bitty ones for
recharging cell phone batteries: outputs 3.7VDC @ 0.35A).
Unfortunately, the device (a portable MP3 player) doesn't
have a jack for DC input coming from an AC adapter.

Could somebody refer me to a resource or reference
(online or otherwise) that contains diagrams for
building a such a thing? I'm handy with electronics,
know how to solder, can read a diagram, have lots of
parts lying around... what I don't have is the know-how
to build a circuit that will supply the correct
voltage/amperage to sub for a AAA battery, that won't
blow up my device. My Google searches have not
borne any fruit as yet.

You can use an LM317 regulator, with two 470 ohm resistors in parallel
between the output and adjust pins, and a 47 ohm resistor from adjust
pin to ground. This gives 1.5VDC. You can also use a 100 ohm pot
fron adj to gnd so you can set it preceisely. But that's not really
necessary. Search for a LM317 data sheet for more info.

Then make a dummy battery out of a piece of wood dowel with screws in
each end, and a two conductor wire running from it to the regulator.

Thanks in advance,

JT

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[Ian Stirling]

You can use an LM317 regulator, with two 470 ohm resistors in parallel
between the output and adjust pins, and a 47 ohm resistor from adjust
pin to ground. This gives 1.5VDC. You can also use a 100 ohm pot
fron adj to gnd so you can set it preceisely. But that's not really
necessary. Search for a LM317 data sheet for more info.

Or just use it as a 3 pin regulator, and connect the adj pin to ground,
giving 1.25V.
Nearly all single cell devices should cope with this, apart from the very
few that only work well with an alkaline battery for the first few minutes.

 

[Dimitrij Klingbeil]

I'd like to build a circuit that will allow me to power
a single AAA battery-driven electronic device, but do
it by modifying DC coming from a typical wall wart
AC adapter (like one of those itty-bitty ones for
recharging cell phone batteries: outputs 3.7VDC @ 0.35A).
Unfortunately, the device (a portable MP3 player) doesn't
have a jack for DC input coming from an AC adapter.

<snip>

A simple way to do so is one-transistor emitter follower with a zener diode
to regulate the base voltage provided by a pullup resistor. You will need
one transistor (preferably npn, should handle several times the power your
device requires without overheating), one resistor (470 Ohm or this like)
and one zener diode (slightly more than 1.7 V). If you construct a dummy
battery empty inside and with screws as contacts (thx, Mr. Watson), you
could (not easily though) place all these parts inside it. WARNING: This
assumes that your wall-wart PS supplies a filtered DC voltage of between 3
and 6 Volts. Otherwise act at your own risk (what you are doing anyway).

See schematic with a fixed font.

+ VCC --------x------ ------- + OUT (battery)
| \ />
--- ---
| | |
| | -----x
--- | |
| | ---!
-- / \
---
|
- VCC -----------------x--------- - OUT (battery)

I hope, this helps, but check everything first with a voltmeter.

Dimitrij