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From: Mike Cook on 9 Apr 2010 11:19
> ** The simplest possible AC converter circuit use two germanium diodes, one
> wired across and one in series with the meter. This is what most anlogue
> multimeters use for the AC volts ranges.
> ...
> .... Phil

Thanks Phil for the simple answer.

This is for measuring output of a simple variac, so yes, the germaniums seem
to be the answer.

Regards,
M

From: John Larkin on 9 Apr 2010 18:45
On Fri, 9 Apr 2010 08:19:34 -0700, Mike Cook <mcham(a)NOTyahoo.com>
wrote:

>> ** The simplest possible AC converter circuit use two germanium diodes, one
>> wired across and one in series with the meter. This is what most anlogue
>> multimeters use for the AC volts ranges.
>> ...
>> .... Phil
>
>Thanks Phil for the simple answer.
>
>This is for measuring output of a simple variac, so yes, the germaniums seem
>to be the answer.
>

Small schottkies will behave about the same. If you use a big series
resistor, as you will in this case, any diode will work.

John

From: Phil Allison on 9 Apr 2010 21:49

"Mike Cook" <

>> ** The simplest possible AC converter circuit use two germanium diodes,
>> one
>> wired across and one in series with the meter. This is what most anlogue
>> multimeters use for the AC volts ranges.
>>
>
> Thanks Phil for the simple answer.
>
> This is for measuring output of a simple variac, so yes, the germaniums
> seem
> to be the answer.


** To prevent over any voltage condition on the Ge diodes, the parallel
one must be connected across the meter and series diode combination.



...... Phil


From: Phil Allison on 10 Apr 2010 00:09

"Phil Allison"

** Additional info:

> Ge diodes begin conducting at less than 100mV.

** Just tested an AAZ15 Ge diode - at 1uA the forward voltage is only
13mV.

A BAT46 Schottky showed 60 mV at the same current.

As the OP had a 45 uA meter movement, this makes the Ge diode a useful
rectifier to around 10mV AC.


> Only a matter of calibrating the scale on the lowest AC range to
> accommodate this.


..... Phil





From: Mike Cook on 10 Apr 2010 00:18
> ** To prevent over any voltage condition on the Ge diodes, the parallel
> one must be connected across the meter and series diode combination.

Thanks Phil. It's newbie tips like this that I need.

Cheers.

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