[time-nuts] Low noise power supply recommendations

J. Forster jfor at quik.com
Wed Jun 15 02:18:02 UTC 2011


I forgot to add that noise on the bridge excitation should not matter much
when the bridge is at null, as the differential mode voltage is zero.

-John

===============


> John,
>
> No, it's DC. I'm trying to meet the original specs of the batteries in not
> only voltage/current, but cleanliness of the current.
>
> Now inside the Fluke 844, it has a chopper, and it uses an AC power supply
> internally to feed its circuitry. The Vishays bridge uses the batteries
> voltage, and one small AC power supply to run the digital portion of the
> bridge for the PPM readout. The bridge itself is half analog and half
> digital. The analog for the measurement, and the digital for the PPM
> difference.
>
> By the way, has anyone ever converted a neon NE-3 driven chopper to using
> LED's? The bulbs have a sqaure wave coming into them of around 100-200 Hz
> if I recall.
>
> Thanks,
>
> Will
>
> *********** REPLY SEPARATOR  ***********
>
> On 6/14/2011 at 6:50 PM J. Forster wrote:
>
>>Is the bridge excitation AC or DC. If it's AC, you may not even need
>>low-noise power supplies.
>>
>>-John
>>
>>==============
>>
>>
>>
>>> Hi Will,
>>>
>>> You could consider building your own power supply system for the
>>> replacement of
>>> the batteries.  Use a separate power transformer which, I suspect,
>>> would
>>> be small
>>> as the current requirements would be low for driving a bridge circuit.
>>>
>>> The main company to look toward for high quality, low noise regulators
> is
>>> Linear
>>> Technology.  Here is a candidate part to look at :
>>> http://www.linear.com/product/LT3082
>>>
>>> This is the lowest noise (33uv/10Hz to 100KHz) low dropout regulator
> that
>>> can
>>> handle regulating 24 volts and is adjustable, meaning use can use this
>>> part for
>>> all three voltages (i.e., three regulators).  You will have to decide
>>> if
>>> it noise
>>> specs are suitable for your needs.  Keep in mind that battery noise is
>>> typically
>>> random whereas the noise out of a regulated system tends to be
>>> constant.
>>>
>>> If you really think you need lower noise then you could consider an
> LT1000
>>> shunt
>>> reference.  Typically the circuit designs for LT1000 type devices are
>>> as
>>> references and lack current capability above about 10 milliamps.
>>> Adding
>>> additional current circuitry would add more noise.  See:
>>>
>>> http://www.linear.com/product/LTZ1000
>>>
>>>
>>> Bill....WB6BNQ
>>>
>>>
>>> Will Matney wrote:
>>>
>>>> Hello,
>>>>
>>>> I am in need of a very clean 24 Vdc power source, to replace some old
>>>> mercury cell batteries with. What would a good low noise, clean, power
>>>> supply be in your recommendations? I thought of using two 12 Vdc
>>>> lead-acid
>>>> batteries in series, and making a charging circuit with regulators,
>>>> but
>>>> I
>>>> am hoping to purchase a good used supply off ebay, etc. The old
>>>> circuit
>>>> used two 12 Vdc snap terminal mercury batteries in series, for 24 Vdc,
>>>> along with a 7 Vdc mercury cell, and two plain AA carbon 1.5 Vdc
>>>> batteries
>>>> in series for 3 volts. Any help and or ideas would be appreciated.
>>>>
>>>> Thanks
>>>>
>>>> Will
>>>>
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>>
>>
>>
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