[time-nuts] Low noise power supply recommendations
jfor at quik.com
Wed Jun 15 02:14:08 UTC 2011
The reason I asked is that most microvolt bridges use choppers and have BP
filters at the chopper frequency, so noise is largely uncorrelated.
On the neon photochoppers, it has been discussed at length several times
on the HP-Agilent Yahyoo Group. A similar thing is used in the 410C. There
are apparently issues with the CdS cells.
> 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
> 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.
> *********** 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.
>>> 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,
>>> 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
>>> Technology. Here is a candidate part to look at :
>>> This is the lowest noise (33uv/10Hz to 100KHz) low dropout regulator
>>> 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
>>> it noise
>>> specs are suitable for your needs. Keep in mind that battery noise is
>>> random whereas the noise out of a regulated system tends to be
>>> If you really think you need lower noise then you could consider an
>>> reference. Typically the circuit designs for LT1000 type devices are
>>> references and lack current capability above about 10 milliamps.
>>> additional current circuitry would add more noise. See:
>>> Will Matney wrote:
>>>> 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
>>>> batteries in series, and making a charging circuit with regulators,
>>>> am hoping to purchase a good used supply off ebay, etc. The old
>>>> 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
>>>> in series for 3 volts. Any help and or ideas would be appreciated.
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