Forums

9V PS

Started by OldGuy September 21, 2013
Looking for the simplest way to this.

AC powered 9V wall-wart or 9V battery powering a circuit.
9V battery is alkaline so is not charged by 9V AC supply.
Load is < 50 ma.

When AC is on, power from the AC to 9v PS.
AC off, power from 9V battery.
9V battery only supplies power when 9V AC is off.

The catch:  the 9V AC PS output may be lower than the 9V battery or 
visa versa.

So a simple two diode scheme will not fly.
Minimum parts and no relays.
Suggestions please.



--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
On Sat, 21 Sep 2013 19:32:39 -0700, OldGuy <OldGuy@spamfree.com>
wrote:

>Looking for the simplest way to this. > >AC powered 9V wall-wart or 9V battery powering a circuit. >9V battery is alkaline so is not charged by 9V AC supply. >Load is < 50 ma. > >When AC is on, power from the AC to 9v PS. >AC off, power from 9V battery. >9V battery only supplies power when 9V AC is off. > >The catch: the 9V AC PS output may be lower than the 9V battery or >visa versa. > >So a simple two diode scheme will not fly. >Minimum parts and no relays. >Suggestions please. > > > >--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
A variation on this... <http://www.analog-innovations.com/SED/PerfectDiodeForChargerIsolation.pdf> What you want to do is determine whether wall-wart is active or not, when active, disconnect battery, and vice versa. Just need to put comparator in the right place. Tomorrow... time for "The White Queen" ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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.
On Sat, 21 Sep 2013 19:32:39 -0700, the renowned OldGuy
<OldGuy@spamfree.com> wrote:

>Looking for the simplest way to this. > >AC powered 9V wall-wart or 9V battery powering a circuit. >9V battery is alkaline so is not charged by 9V AC supply. >Load is < 50 ma. > >When AC is on, power from the AC to 9v PS. >AC off, power from 9V battery. >9V battery only supplies power when 9V AC is off. > >The catch: the 9V AC PS output may be lower than the 9V battery or >visa versa. > >So a simple two diode scheme will not fly. >Minimum parts and no relays. >Suggestions please.
Can't use the switch in the barrel connector? A changeover SSR + dual diode + resistor will work, and may be the simplest- 3 parts or 4 simple parts- but probably not the cheapest. Eg. http://media.digikey.com/pdf/Data%20Sheets/Toshiba%20PDFs/TLP4006G.pdf The cheapest/simplest might be a prebiased transistor, a dual diode and depletion mode MOSFET and a resistor-- 4 parts, or 7 simple parts. Maybe someone else has other ideas.. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
On Sat, 21 Sep 2013 23:04:31 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>On Sat, 21 Sep 2013 19:32:39 -0700, the renowned OldGuy ><OldGuy@spamfree.com> wrote: > >>Looking for the simplest way to this. >> >>AC powered 9V wall-wart or 9V battery powering a circuit. >>9V battery is alkaline so is not charged by 9V AC supply. >>Load is < 50 ma. >> >>When AC is on, power from the AC to 9v PS. >>AC off, power from 9V battery. >>9V battery only supplies power when 9V AC is off. >> >>The catch: the 9V AC PS output may be lower than the 9V battery or >>visa versa. >> >>So a simple two diode scheme will not fly. >>Minimum parts and no relays. >>Suggestions please. > >Can't use the switch in the barrel connector? > >A changeover SSR + dual diode + resistor will work, and may be the >simplest- 3 parts or 4 simple parts- but probably not the cheapest. > >Eg. >http://media.digikey.com/pdf/Data%20Sheets/Toshiba%20PDFs/TLP4006G.pdf
Those belly-to-belly body-to-body MOS devices solve the issue of a over/under conduction. If you have a barrel connector that opens a switch to ground when the plug is inserted, it's a trivial exercise with 2 discrete PMOS devices and one resistor.
> >The cheapest/simplest might be a prebiased transistor, a dual diode >and depletion mode MOSFET and a resistor-- 4 parts, or 7 simple parts. > >Maybe someone else has other ideas.. > > > > >Best regards, >Spehro Pefhany
...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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.
On 9/21/2013 10:32 PM, OldGuy wrote:
> Looking for the simplest way to this. > > AC powered 9V wall-wart or 9V battery powering a circuit. > 9V battery is alkaline so is not charged by 9V AC supply. > Load is < 50 ma. > > When AC is on, power from the AC to 9v PS. > AC off, power from 9V battery. > 9V battery only supplies power when 9V AC is off. > > The catch: the 9V AC PS output may be lower than the 9V battery or visa > versa. > > So a simple two diode scheme will not fly. > Minimum parts and no relays. > Suggestions please. > > > > --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Focusing on just the minimum parts requirement, here are 2 possibilities: the first uses 3 parts and the second uses 2 parts 3 parts (with drawback of extra diode drop when powered from battery): Battery - ------------------------+ | D1 D2 | Battery + --->|--->|---+---load---+ | | Supply + --->|--------+ | D3 | | Supply - ------------------------+ I know you didn't want relays, but here's one anyway, in case you change your mind: +-----------------+ | | +------|<-----+ | ------ | | v | Wall |+ ---+---[Relay]---+ ---o---[load]---+ | Wart | | ^ | |9V DC | | | Gnd |Supply|- ---+ | | ------ | | | Gnd Gnd | | | Battery - ---+ | | Battery + ---------------------+ An Omron G5V-1 9V relay and a diode will do it. The relay will transfer as low as 7.2 volts. Not the most elegant solution, but less than $3.00 and easy to implement. Ed
On Sat, 21 Sep 2013 19:32:39 -0700, OldGuy <OldGuy@spamfree.com>
wrote:

>Looking for the simplest way to this. > >AC powered 9V wall-wart or 9V battery powering a circuit. >9V battery is alkaline so is not charged by 9V AC supply. >Load is < 50 ma. > >When AC is on, power from the AC to 9v PS. >AC off, power from 9V battery. >9V battery only supplies power when 9V AC is off. > >The catch: the 9V AC PS output may be lower than the 9V battery or >visa versa. > >So a simple two diode scheme will not fly. >Minimum parts and no relays. >Suggestions please. > > > >--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
From a previous SED thread, where an unregulated wall-wart was involved... <http://www.analog-innovations.com/SED/PowerSwitching_Battery-Wallwart.pdf> If I understand your situation correctly, it might be as simple as using a barrel connector with a built-in switch (from R/S, as I remember buying them)... <http://www.analog-innovations.com/SED/PowerSwitching_OldGuy.pdf> If you have a more complex situation, like wall-wart hard-wired in place, I have other solutions to detect that it's live and switch accordingly. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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.
On Sun, 22 Sep 2013 08:55:44 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Sat, 21 Sep 2013 19:32:39 -0700, OldGuy <OldGuy@spamfree.com> >wrote: > >>Looking for the simplest way to this. >> >>AC powered 9V wall-wart or 9V battery powering a circuit. >>9V battery is alkaline so is not charged by 9V AC supply. >>Load is < 50 ma. >> >>When AC is on, power from the AC to 9v PS. >>AC off, power from 9V battery. >>9V battery only supplies power when 9V AC is off. >> >>The catch: the 9V AC PS output may be lower than the 9V battery or >>visa versa. >> >>So a simple two diode scheme will not fly. >>Minimum parts and no relays. >>Suggestions please. >> >> >> >>--- news://freenews.netfront.net/ - complaints: news@netfront.net --- > >From a previous SED thread, where an unregulated wall-wart was >involved... > > ><http://www.analog-innovations.com/SED/PowerSwitching_Battery-Wallwart.pdf> > >If I understand your situation correctly, it might be as simple as >using a barrel connector with a built-in switch (from R/S, as I >remember buying them)... > > <http://www.analog-innovations.com/SED/PowerSwitching_OldGuy.pdf> > >If you have a more complex situation, like wall-wart hard-wired in >place, I have other solutions to detect that it's live and switch >accordingly. > > ...Jim Thompson
Found the jack on the SparkFun site... <https://www.sparkfun.com/products/119> ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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.
On Sat, 21 Sep 2013 19:32:39 -0700, OldGuy <OldGuy@spamfree.com>
wrote:

>Looking for the simplest way to this. > >AC powered 9V wall-wart or 9V battery powering a circuit. >9V battery is alkaline so is not charged by 9V AC supply. >Load is < 50 ma. > >When AC is on, power from the AC to 9v PS. >AC off, power from 9V battery. >9V battery only supplies power when 9V AC is off. > >The catch: the 9V AC PS output may be lower than the 9V battery or >visa versa. > >So a simple two diode scheme will not fly. >Minimum parts and no relays. >Suggestions please.
--- Version 4 SHEET 1 1172 680 WIRE 144 -32 -96 -32 WIRE 352 -32 240 -32 WIRE 608 -32 352 -32 WIRE 832 -32 704 -32 WIRE 656 64 656 32 WIRE 192 80 192 32 WIRE 352 80 352 -32 WIRE 192 192 192 160 WIRE 704 192 544 192 WIRE 832 192 832 -32 WIRE 832 192 784 192 WIRE -96 240 -96 -32 WIRE -16 240 -96 240 WIRE 128 240 64 240 WIRE 656 240 656 144 WIRE 544 288 544 192 WIRE 544 288 512 288 WIRE 592 288 544 288 WIRE -96 336 -96 240 WIRE -16 336 -96 336 WIRE 448 336 64 336 WIRE -96 384 -96 336 WIRE 832 384 832 192 WIRE -96 512 -96 464 WIRE 192 512 192 288 WIRE 192 512 -96 512 WIRE 352 512 352 160 WIRE 352 512 192 512 WIRE 512 512 512 384 WIRE 512 512 352 512 WIRE 656 512 656 336 WIRE 656 512 512 512 WIRE 832 512 832 464 WIRE 832 512 656 512 WIRE -96 592 -96 512 FLAG -96 592 0 SYMBOL res 80 224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL pnp 240 32 M270 WINDOW 0 7 148 VLeft 2 WINDOW 3 31 174 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL npn 128 192 R0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL res 176 64 R0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL voltage -96 368 R0 WINDOW 3 24 96 Invisible 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value PULSE(0 9 1 1u 1u 1 2) SYMATTR InstName V1 SYMBOL res 336 64 R0 WINDOW 0 40 47 Left 2 SYMATTR InstName R4 SYMATTR Value 180 SYMBOL pnp 608 32 R270 WINDOW 0 7 148 VLeft 2 WINDOW 3 31 174 VLeft 2 SYMATTR InstName Q2 SYMATTR Value 2N3906 SYMBOL npn 592 240 R0 SYMATTR InstName Q5 SYMATTR Value 2N3904 SYMBOL res 672 48 M0 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL voltage 832 368 M0 WINDOW 3 24 96 Invisible 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value 9 SYMATTR InstName V2 SYMBOL npn 448 288 R0 SYMATTR InstName Q4 SYMATTR Value 2N3904 SYMBOL res 80 320 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 100k SYMBOL res 800 176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 10k TEXT -80 544 Left 2 !.tran 10 TEXT -56 424 Left 2 ;WALL-WART TEXT 696 424 Left 2 ;BATTERY TEXT 360 168 Left 2 ;LOAD TEXT 32 544 Left 2 ;John Fields TEXT 32 576 Left 2 ;22 September 2013 -- JF
On Sun, 22 Sep 2013 09:51:19 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Sun, 22 Sep 2013 08:55:44 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Sat, 21 Sep 2013 19:32:39 -0700, OldGuy <OldGuy@spamfree.com> >>wrote: >> >>>Looking for the simplest way to this. >>> >>>AC powered 9V wall-wart or 9V battery powering a circuit. >>>9V battery is alkaline so is not charged by 9V AC supply. >>>Load is < 50 ma. >>> >>>When AC is on, power from the AC to 9v PS. >>>AC off, power from 9V battery. >>>9V battery only supplies power when 9V AC is off. >>> >>>The catch: the 9V AC PS output may be lower than the 9V battery or >>>visa versa. >>> >>>So a simple two diode scheme will not fly. >>>Minimum parts and no relays. >>>Suggestions please. >>> >>> >>> >>>--- news://freenews.netfront.net/ - complaints: news@netfront.net --- >> >>From a previous SED thread, where an unregulated wall-wart was >>involved... >> >> >><http://www.analog-innovations.com/SED/PowerSwitching_Battery-Wallwart.pdf> >> >>If I understand your situation correctly, it might be as simple as >>using a barrel connector with a built-in switch (from R/S, as I >>remember buying them)... >> >> <http://www.analog-innovations.com/SED/PowerSwitching_OldGuy.pdf> >> >>If you have a more complex situation, like wall-wart hard-wired in >>place, I have other solutions to detect that it's live and switch >>accordingly. >> >> ...Jim Thompson > >Found the jack on the SparkFun site... > ><https://www.sparkfun.com/products/119> > > ...Jim Thompson
Also on Digikey, with more technical detail... <http://www.digikey.com/product-detail/en/PJ-202A/CP-202A-ND/252007> Some may wonder how I made a symbol that can show as an open or closed switch AND functionally perform that way... PSpice can do conditional netlisting templates. When the (text) character "|" is present (switch shows closed because that "text" does the visual closing), the presence of that "text" satisfies a conditional and it netlists as a wire... otherwise an open ;-) I also do fuses, snip-out trim, and laser cut simulations that way. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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.
On Sat, 21 Sep 2013 19:32:39 -0700, OldGuy <OldGuy@spamfree.com>
wrote:

>Looking for the simplest way to this. > >AC powered 9V wall-wart or 9V battery powering a circuit. >9V battery is alkaline so is not charged by 9V AC supply. >Load is < 50 ma. > >When AC is on, power from the AC to 9v PS. >AC off, power from 9V battery. >9V battery only supplies power when 9V AC is off. > >The catch: the 9V AC PS output may be lower than the 9V battery or >visa versa. > >So a simple two diode scheme will not fly. >Minimum parts and no relays. >Suggestions please.
BTW, having recently gone through the thinking of a similar situation (high-reliability and at maybe 100x or 1000x the current, but basically the same concept), you might want to give some thought to your actual requirements vis-a-vis various situations on either power port. In particular, are glitches of any concern? Consider the "simple" solution with a relay- and input coming from a big AC adapter. Unplug the barrel connector and you get a brief glitch (maybe a millisecond or two) as the contacts transfer. If the AC power fails or is switched off, you could get a 1-second glitch with voltage out dropping to maybe a volt before the battery takes over. In a pathological situation, the AC adapter output could drop to about half a volt if it is very cold without the relay dropping out (the spec says "must drop out" is 5% of rated voltage, IIRC), which would likely be outside the operating range of whatever you've got this connected to.