How do I get -15V ?

[Steve Joblin]

I am using a component (a Tamura L08P***D15 Series Current Sensor) that requires a +15v and a -15v power source.  I have a 24 volt battery.  I know how to get the +15v by using a regulator, but I'm not quite sure the best way to get -15v.  The tutorial describes using a MAX232 IC to get -15v, but I was wondering if there are any other approaches that folks have used.  If I do use a MAX22, I have a few quick questions:

1.  Do I need any other components or just a MAX232?
2.  Which pin do I connect the +15v going into the MAX232?

[Admin]

If you use a MAX232, you will want to use capacitors to stabilize the output voltages.

Send your power to Vcc.

Check the datasheet for details, should all be there.

Just a side note . . . if your device isn't going to be portable, perhaps just use a tabletop power supply for the negative voltage?

[frank26080115]

http://www.national.com/mpf/LM/LM7915.html

cheers

[Steve Joblin]

Thanks Admin!

Frank - I was looking at that exact part (LM7915), but the way I read the datasheet, it looked like you need to feed it a negative voltage to get a regulated negative voltage out.  Am I not reading it correctly?

[frank26080115]

There's a trick to using this, if you look at it's pinout (front facing you, pins pointing down), input is in the middle, ground is on the left, if you connect input to the battery's negative, and ground to the battery's positive (pretending it was a normal everyday positive regulator), you make the input negative. BUT don't connect the ground pin to the ground of the circuit, connect the battery's negative to the ground of the circuit as usual.

[Steve Joblin]

Thanks so much!  This is exactly what I was looking for!!!!

[airman00]

There's a trick to using this, if you look at it's pinout (front facing you, pins pointing down), input is in the middle, ground is on the left, if you connect input to the battery's negative, and ground to the battery's positive (pretending it was a normal everyday positive regulator), you make the input negative. BUT don't connect the ground pin to the ground of the circuit, connect the battery's negative to ground as usual.

neat trick 

[Steel_monkey]

Frank26080115, have You tested this schematic? It looks a little strange- You step-up voltage with only linear circuits ( no switching), getting 30 Volts from 24. Linear cirquit make voltage only less, no more. And Proteus tells the same.
Steve Joblin: how many current your device consume from -15 V? And how stable voltage should be? If You are not using prescision components there, and consumption is low (5 mA) You can use switching capacitors inverter ( for example 2 LMC7660), or something like ADP1111 fore more current.

[Steve Joblin]

Thanks for the insights Steel_monkey!  I will have two of these devices... each consumes 12mA.

[frank26080115]

Frank26080115, have You tested this schematic? It looks a little strange- You step-up voltage with only linear circuits ( no switching), getting 30 Volts from 24. Linear cirquit make voltage only less, no more. And Proteus tells the same.
Steve Joblin: how many current your device consume from -15 V? And how stable voltage should be? If You are not using prescision components there, and consumption is low (5 mA) You can use switching capacitors inverter ( for example 2 LMC7660), or something like ADP1111 fore more current.

I only have 7805s and 7905s right now, I'll test and let you know, but I'm fairly certain.

[Steel_monkey]

     So 36 mA is required ( 12 mA as a reserve), and switching caps inverter will be too weak. So, conventional inverter should be used ( I can`t say I know voltage regulators very much, but everything is explained in datas). So look through this datas: http://www.ti.com/lit/gpn/mc33063a or http://www.ti.com/lit/gpn/tl497a .They are both voltage regulators, few external components required. Datasheets contains all necessary calculations, and price is more then adequate. They should give enough current for Your sensors. Perhaps, best idea will be first convert 24 to -24 and then use 7915, it will give better stability and 7815 will not be overwatted. Also a little question: is 24 V motor power or it also feed logics?
    frank26080115, Proteus tells following (sorry, haven`t seen next post ):

[frank26080115]

Crap, I don't think the 7915 will work

[Steve Joblin]

Mike Green on the Parallax forum suggested using a ICL7662 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=ICL7662CPA%2B-ND

[Steel_monkey]

It is simple switching capacirots inverter ( I mentioned them before). According to datasheet, with 12 mA consumption load, output voltage would be nearly 14.25 Volts, and even lesser with more consumtion. In datasheet on sensor it is told to have 15 Volts +-5%, what means +-0.75 Volts, so using one ICL7662 will be nearly on the border of correct work. It is told in datasheet it is possible to connect ICL7662 in parallel to lower output resistaance- two ICs should be enough ( voltage will be 14.6, so  acceptable). Choose capacitors and draw schematic according to datasheet.
P.S. They are reltively expensive by comparison with MC33063.

[Crooksie]

You can try a circuit like this:

Gives a regulated -15V output, based on a 555 timer ic.  Tried and tested, works really well.

EDIT:
Looking at it again I'm not sure if this circuit will be any good in your situation, as 24V is abit much for a 555 timer ic, you could however power this circuit from another regulator, although you might want to look at switching regulators as a lot of energy could be used up by this circuit then.