[GPS_Standard] -5 to +5 Voltage Source

[SP2IQW]

My 3 cents in this topic.

If we do not have separate negative power supply the best way is to use
a MAX662/LMC662/ICL7662 which makes negative voltage by charge pumping
from a positive voltage  (4.5-20V range), followed by a 79L05 regulator.
We can get -5V also from MAX232  TTL/RS232 converter (unloaded pin 6
provides -10V), it should be filtered and regulated for example with 79L05.

Please keep in mind that voltage drop of 79L05 voltage regulator is
typically 2V and quiescent current  of a regulator is in the range 3-5mA
and it may be hard to get enough current from MAX232 when higher current
operational amplifier will be used instead of OPA2705.

If we don't need negative voltage to control OCXO we can even connect
-5V power path to ground. The OPA2705 amplifier works as rail to rail on
the input and output what is shown on the original diagram.


The known problem is voltage translating between 3,3V CMOS level GPS
receiver and 5V logic PIC CPU.
This year Texas Instruments introduced  SN74LV1T...series logic level
translators.
http://www.ti.com/lsds/ti/logic/little-logic-little-translation.page?DCMP=hval_sll_log_sn74lv1t_en&HQS=hval-sll-log-sn74lv1t-pp-en
Simply insert non-inverting functor as SN74LV1T125/126 or ..08 between
low voltage GPS receiver and 5V PIC microcontroller.

73, de Michal
sp2iqw



W dniu 2014-12-14 o 04:11, Dave Platt pisze:
>> I'm having difficulty understanding how to create the proper voltage source
>> for the VE2ZAZ control board, -5 to +5 volts.  Any suggestions?
> There are several approaches.
>
> If you start with a single-voltage supply (say, a +12 or +24 - whatever
> your oscillator requires) you can add an additional regulator to get a
> clean +5 supply for the board's oscillator-control output.  Since you
> only need a small current, a simple 78L05 regulator and a couple of
> filter caps would be all you need.
>
> The -5 is more difficult.  The most straightforward way is to use a
> commercially-made or home-made power supply with both positive and
> negative outputs... say, a +/- 15 (these are relatively common) and then
> use a negative voltage regulator such as a 7905 to regulate the -15 down
> to -5.
>
> You could buy a kit such as the Chaney C6895 from Electronics
> Goldmine... this has three variable output voltages (positive and
> negative up to 15 volts, at 400 mA, and positive up to 21 volts at 1
> ampere).  This might be your best bet, if 1 amp is enough to run the
> oscillator with its heater and the main VE2ZAZ input - the two
> low-current outputs could be set to +5 and -5 and provided to the VE2ZAZ
> output circuit.
>
> It *is* possible to start with a single-voltage DC supply, and generate
> positive and negative voltages from it.  It's a bit tricky.  One
> approach is to use a switching-type "inverting regulator" to create the
> negative voltage.  Alltronics has a +12 in, -5 out (Astec AA7600), $8
> for two.  These switching inverters might not be a great solution for a
> GPSDO where you want really low noise, though.
>
> Another approach is to start with something like a 24-volt DC supply,
> and use a 7805 linear regulator to create an "artificial ground" (which
> then becomes the "GND" power input to your VE2ZAZ board).
>
> If I were you I'd probably look for a multiple-output DC power supply...
> Electronics Goldmine, Alltronics, All Electronics, Marlin P Jones are
> all good on-line vendors to check.
>
> And... as an out-of-the-box possibility - although your HP oscillator
> has a -5 to +5 tuning range, there's no law that says you have to
> actually *use* the whole tuning range.  You could have the VE2ZAZ board
> put out a tuning voltage between 0 and 5 (so no negative supply
> required) and use the HP oscillator's "FREQ ADJUST" trimmer to
> rough-tune the oscillator so that it's right about on-frequency when the
> VE2ZAZ is feeding a mid-scale output (2.5 volts) to the oscillator's
> EFC input.
>
> This would let you get away with just positive power supply voltages to
> the oscillator oven, oscillator input, and VE2ZAZ.
>
>
>
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