[NLRS] -12 Volt Bias Supply for a Trimble GPS unit?

[Dr. Gerald N. Johnson]

There are a number of isolated DC-DC converters with a fractional watt 
power capability sometimes in a 4 pin SIP package for under $5 at Mouser 
and Digi-Key. For enough 12 volt output to wire in series with the 12 
volt supply for running a 28 volt relay the cost goes up to about $8. No 
doubt there are many on epay too, if the sellers actually know what they 
have. Very similar to the 12 in 5 volt output part DEMI uses for bias in 
the 10 GHz 3 watt amplifier.

A 5 volt output one from DK is PM1205.

Some others are: 
www.digikey.com/product-search/en?FV=fff40042%2Cfff800df%2C11800099%2C16fc000a%2C16fc0020%2C170000c7%2C17d4002c&k=dc+to+dc+.25w&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

A 15 volt unregulated output 2 watt (for relays) from Mouser is 
RI-1215S. 12 volt unregulated output is at:
www.mouser.com/Power/DC-DC-Converters/_/N-5gc7?Keyword=ri1212s&FS=True

An alternative is a step down switching regulator. Its input needs to be 
able to handle more than 24 volts. One that I'm sure will work uses the 
LM2596S-12 or -ADJ chip. Chuck, WA3INC sells them assembled on line for 
$6.95 and Marlin P. Jones and associates sells essentially the same 
assembly for $3.95. MPJA more than makes up with their shipping.

With the step down switcher, one connects the positive output to ground, 
the +12 to the regular input and uses the board/chip ground as the 
negative 12. The data sheet suggests a circuit modification to reduce 
the peak current when power is first applied, but slows the output 
voltage rise, I'm sure. Details are on the chip maker's data sheet and 
applications note.

One could use other schemes, I not sure the 7660 used in many a preamp 
will survive on a 12 volts supply. I know a 555 can be used as a power 
oscillator with its output pin swinging between essentially ground and 
+12 then capacitor couple a half wave peak to peak rectifier set for 
negative output. That circuit is also known as a voltage doubler. Uses 
two diodes and two capacitors. I've seen vintage scanners use a low 
power oscillator, then an audio output IC to drive a transformer and 
rectifier for a fluorescent display supply, that just as easily could 
have been a negative supply. The MAX232 and 233 have such an inverter 
built in. The 232 needs external capacitors, the 233 (or 333) doesn't 
need them. Then there are batteries and squirrel driven generators. ;<)

73, Jerry, K0CQ

On 12/1/2013 12:57 PM,  Jim Froemke wrote:
>
>
> Does anyone know of a small, low-cost source for a +12 VDC to -12VDC
> polarity converter that could be used to supply the - 12 VDC +/- 10%, 10 mA
> voltage for the "prime OXCO" within a Trimble Thunderbolt GPS unit?
>
> 73, Jim
>
> K0MHC/rover
>
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