Getting + /-5v from 9-12vdc adapter (1spot)

[tysonlt]

Hi all!

In a circuit I am building, I want to run a PIC and a CD4053 on bipolar power, with the uC on 0v - +5v, and the cmos on -5/+5.

I have a 1spot and another generic 12vdc adapter, and I would like to be able to use either.

I was going to use RG's circuit with the max1044, but then read that it doesn't like 10v, and the 1spot can get close to that.

Obviously I could use a 7809 to get 9v from the 12v adapter, but what about the 1spot? Is there a voltage regulator that can take between 9.4 and 12v and spit out a safe 9? Or is there another chip apart from the max1044 that is not so sensitive to the incoming voltage?

[lonewolf]

you can use a zener diode with a resistor to regulate dc..anything from 4.5 to 12v and up...just use a large enough wattage(1watt)

[tysonlt]

Oh wow, fastest reply ever! Made my night! Watching tennis, learning about diodes, ahhhh....

Now to Google zener diodes!

(As an aside, I loved diodes when I was a kid. Waited for ages to get some germanium diodes to make a matchbox crystal radio.)

Thanks

[petemoore]

  You get a DC voltage drop across diode [easily measured].
   A string of GE's or Si's with X voltage across them [note polarity] add, drop 'some' voltage...drop some more with another series diode, choose your diode DCV drop easily, go by the data sheets or measure the diode threshold voltage, then put a DC voltage [in excess of the total diode drops] across them and measure the actual voltage drop.
   Regulators require 2vdc for operation, when it is not avaialbe they don't work.
   The 1Spot is regulated output.
   I started typing suggestions but realize the application is what determines how to criticize or what won't be noticed in a power supply.
   Does the 5v supply needs to be regulated? 5vdc that is exceeded by >2vdc with either adapter [2vdc is what a 7805 requires for it's operation] so a regulator for that will have a supply...either way, whether the increased voltage drop using the 12vdc [if that is what it is rated at, it probably is closer to 14vdc with a light load on it] makes heat dissipation a problem is the only 'hurdle' I forsee getting 5VDC regulated from 7v - say 15v supply range...I haven't read the data sheet so if you're expecting a 'big volt drop' across a regulator, read the data sheet [to see if you're exceeding the rating] and expect a lot of current to produce fantastic' heat in the chip and you'll need a heat sink on it.
   If the CMOS is running audio you'll want it regulated.
   Perhaps you/the other equipment etc. won't mind the CMOS voltage being 'close' instead of precisely as stated...
   In such case would simply splitting the 9.4vdc regulated output of the 1Spot with a voltage divider be sufficient for the CMOS / or would you like both the +/- rails regulated ?
   The 'hurdle' is more like a wall if 10vdc is acutally needed from a 1spot or 9vdc is to be regulated from 9.4vdc....a switching scheme here might do it but isn't suggestable for damage control...If I Had to have it both ways, a switching jack scheme and separate [un-mix-up-able] jacks for one [wired without internal regulator] and the other [the 1spots regulated...
   anyway without knowing the CMOS application [and assuming the 5vdc needs to be regulated]...there's some suggestions to scheme on...
   Power Supplies for Effects is a good read at GEO.
   The 5vdc should tack on to any DCv above 7v, expect heat dissipation to increase with greater voltage drop across the chip or increased current. 
   Without knowing the application suggestions as to what you might want for the supply is hit or miss, that said you might be able to voltage divide either supply with resistors/filtercaps, so you can use the 1spot output, and put whatever regulator you need to make 'other adapters' work outside the box, again, heat dissipation...perhaps a 7809 or 7810 runs cool enough to put it in a teeny enclosure spliced into the 12vdc output wire.
   
   
   
   

[tysonlt]

Thanks for the ideas. The application, with schematic, is here:

http://www.diystompboxes.com/smfforum/index.php?topic=95733.msg830770.msg#830770

This is just one cmos switch, but I plan to build one with 10 switches and midi output. I can't wait to build it but I have to understand all the details before touching the soldering iron... It's an aspergers thing

I plan to have pic running from gnd to +5, and cmos from +/-5 to give it more headroom.

Could I just regulate down to 5v with a 7805, which can take from 7 to 35v, and then use the max1044 to get -5v for the cmos? Sound reasonable?

[moosapotamus]

Yes, the 7805 is a positive voltage regulator. Feed it at least 8VDC and will output +5V. For -5v, use a 7905 (negative voltage regulator). Google up the datasheets for typical application circuits.

~ Charlie

[liquids]

I was going to use RG's circuit with the max1044, but then read that it doesn't like 10v, and the 1spot can get close to that.

10v really should be fine, unless your voltage is constantly fluxuating significantly above that.  It's not reccomended, but people have fed this chip 12v DC repeatedly and claimed not to have an issue.

That said, the LT1054 is a great chip that is quieter, outputs more current, handles 15vDC nicely, and sometimes is cheaper.  The datasheet has everything you need for voltage doubling and generating a negative DC voltage from a positive DC voltage.

Obviously I could use a 7809 to get 9v from the 12v adapter, but what about the 1spot? Is there a voltage regulator that can take between 9.4 and 12v and spit out a safe 9? Or is there another chip apart from the max1044 that is not so sensitive to the incoming voltage?

I don't know anything about PIC, or why you need a bipolar supply.  Howver, you could regulate the one spot down to 5v, then use that as your positive rail.  Simultaneously feed that to a voltage inverter chip (max1044 or LT1054, etc) and you have a negative voltage.

If you plan to do a few bipolar-power circuits, it's worthwhile to check out how to rectify AC into bipolar power.  Even if you don't use it now, it's something you'll have as an option later on if you choose to go in that direction.  Great info available on geofex.com in that regard.  And cheap AC power supplies are available from jameco if you are in the USA or really, any pack-rats storage area should have a handful of AC wall worts to (carefully) mess around with.

[PRR]

> between 9.4 and 12v and spit out a safe 9?

Why 9 ?

You want -5V. You need only teensy-weensy current if only biasing the 4053's logic. You _have_ +5V.

Simple power inverter will take +5V and give -4.5V which is close enough. (As Matthew said while I was typing.)

The power is SO low that you don't need a dedicated power chip. Do you have a spare output on the CPU? Can you program it to toggle hi/lo at some rate 50KHz-500KHz? Two diodes and two capacitors can double-down to give your negative rail. It may sag bad with 1mA, but the CMOS only needs a few uA.

[tysonlt]

I guess the only reason I want bipolar power is that I read somewhere on this forum (do you like my scientific process?) that it is better to use 4053's at bipolar power so that the guitar signal is biased at 0v... because that is safer for any given pedal that might be attached to it. I'll try to find that thread.

Also because I want to be able to feed it with a grounded 9vdc adapter, if I went with normal rails I'd only be able to regulate to about 7v, since vregs want 2v more than their output. Just wondering whether 7v will provide enough headroom for high-gain pedals or pre-amped signals from amp effects loops.

[tysonlt]

Here is the thread that suggests that bipolar is better for switching external effects:

http://www.diystompboxes.com/smfforum/index.php?topic=86026.msg719920#msg719920

But if you want the effects to be outside the box connected by plugs then I would absolutely go for switching at 0VDC.