Auto-detecting battery power for circuit

Nov 12, 2011 45 Replies
P

Hello,



I have a circuit that works off of 3V. I get the 3V in two different ways, one is through a 9V battery that plugs into a DC power barrel receptacle that goes to a 3V regulator, and the other is from a 3V pin that is available on the circuit. I'm wondering if there is a way the circuit could automatically use the 3V pin if there's no battery plugged into the DC barrel receptacle, and if there is a battery plugged in it would switch and use the 3V coming out of the 3V regulator.



At first I was thinking about OR'ing the power sources through some diodes... but since I'm working with 3V, I really don't want to give up a diode voltage drop on my power. Next I started looking at the DC barrel receptacles that have built in switches (I've never used these before) and seems like this would be a good option if I was working with the same voltages, but since one of my voltage is 9V and the other is 3V, I need the 3V pin to bypass the voltage regulator, and the 9V to go to the voltage regulator... so they are going to different places on my circuit (different sides of the regulator essentially).



any suggestions would be appreciated, much thanks!


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J

Off on a "honey-do" trip to the grocer :-), so no time to adapt to your needs, but look these over...

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...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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P

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

thank you i will look these over

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J

Use a depletion mode FET as a normally on switch and use the external 9V to turn off the internal 3 volts? Just a thought..

Jamie

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W

Some 'barrel connector' sockets have three contacts, one (+), one (-), and a third that implements an NC switch to the barrel, which goes open if there is a jack in the socket.

So, can you logically use that switch contact to implement the power supply switchover?

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M

.

That seems like the best approach to me, but I've spent quite a while trying to figure how to wire this, and I can't.... I'm not sure if it'as possible. The problem is that my two voltages go to two different places, the 9V (when the battery is plugged in) goes to the input of the voltage regulator and the 3V would need to be isolated from the circuit, then if you unplug the battery the 3V needs to go to the output pin of the voltage regulator (because from there it can go to the rest of the circuit).... maybe this isn't logically possible with a spst switch?

thanks

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P

.

That seems like the best approach to me, but I've spent quite a while trying to figure how to wire this, and I can't.... I'm not sure if it'as possible. The problem is that my two voltages go to two different places, the 9V (when the battery is plugged in) goes to the input of the voltage regulator and the 3V would need to be isolated from the circuit, then if you unplug the battery the 3V needs to go to the output pin of the voltage regulator (because from there it can go to the rest of the circuit).... maybe this isn't logically possible with a spst switch? thanks

Vote
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P

.

That seems like the best approach to me, but I've spent quite a while trying to figure how to wire this, and I can't.... I'm not sure if it'as possible. The problem is that my two voltages go to two different places, the 9V (when the battery is plugged in) goes to the input of the voltage regulator and the 3V would need to be isolated from the circuit, then if you unplug the battery the 3V needs to go to the output pin of the voltage regulator (because from there it can go to the rest of the circuit).... maybe this isn't logically possible with a spst switch? thanks

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J

What chip (or circuit) is used for the regulator?

"3V pin"? Does it always have power or is it connected and disconnected depending on use?

...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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P

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

The 3V pin is always connected to 3V, the regulator I'm using is

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thanks

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J

[snip]

Why such a regulator when you have a 9V input? LDO's can be painful. ...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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T

The MCP1825S is only rated for 6.5 volts max input. Are you feeding it 9 volts?

tm

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J

]snip]

Huh? That datasheet says maximum input voltage = 6.5V ???? ...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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P

nt

the

DC

=A0 =A0 =A0 ...Jim Thompson

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

oops! yall are right, I'll need to spec out a new part there, thanks.

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J

[snip]

And tell us your operating currents while you're at it ;-) ...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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R

Yes, they make power jacks that with some kind of third contact arrangement, do exactly that. Just shop around at maybe Digi-key or Mouser or Newark or whatever.

But I wonder, for battery, why use a 9V battery and regulate it down? Why not just use a 3V battery, like 2x 1.5V?

Have Fun! Rich

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P

e

well, I'm thinking that a 9V would last longer. I've found some of these third contact power jacks, just can't wrap my head around a way to use it when I have two different points in my circuit for the voltage...

thanks

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P

nt

the

DC

=A0 =A0 =A0 ...Jim Thompson

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

Right, I got the wrong part, I'll spec out a better one

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P

erent

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=A0 =A0 =A0 ...Jim Thompson

...

.

=A0 =A0 =A0 ...Jim Thompson

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

15mA
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J

How much current? ...Jim Thompson

| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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