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From: markp on 25 Jul 2010 12:07
>
> markp wrote:
>
> Hey mark, I have already looked at the LTC3108 chip.yes it's used for
> energy harvesting, but it needs a dc input voltage. I plan to use that
> chip, but before that I have to rectify my AC voltage.
>

Not true, the application circuit actually produces an AC source from DC by
using a resonant oscillator which is then synchronously rectified. The
device can be used with AC, see page 14: "Any source whose peak voltage
exceeds 2.5V AC or 5V DC can be connected to the C1 input through a
current-limiting resistor where it will be rectified/peak detected." In fact
it mentions vibrational sensors as a possible input source which is very
likely to be AC.

So it seems by placing a 1:12.5 step-up transformer from your 200mV input
you could produce a 2.5V AC signal suitable for use.

Mark.


From: Jim Thompson on 25 Jul 2010 12:31
On Sun, 25 Jul 2010 02:25:32 +0000,
findprahul_at_yahoo_dot_co_dot_uk(a)foo.com (rahulponna) wrote:

>rahulponna had written this in response to
>http://www.electrondepot.com/electrodesign/Re-AC-to-DC-conversion-without-using-diodes-and-no-external-484602-.htm
> :
>
>Jamie wrote:
>
>I am looking at a frequency of 950MHz. the input voltage is 200mV (peak).
>Also for precision rectifier I have to use external supply for the op amp.
>I need to make all my electronics work with the harvested energy.
>
>
[snip]

950MHz is a RFID "TAG" frequency.

What is the source impedance? How about a transmission line
transformer?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Spice is like a sports car...
Only as good as the person behind the wheel.
From: Paul Keinanen on 25 Jul 2010 12:44
On Sun, 25 Jul 2010 17:07:54 +0100, "markp" <map.nospam(a)f2s.com>
wrote:

>>
>> markp wrote:
>>
>> Hey mark, I have already looked at the LTC3108 chip.yes it's used for
>> energy harvesting, but it needs a dc input voltage. I plan to use that
>> chip, but before that I have to rectify my AC voltage.
>>
>
>Not true, the application circuit actually produces an AC source from DC by
>using a resonant oscillator which is then synchronously rectified. The
>device can be used with AC, see page 14: "Any source whose peak voltage
>exceeds 2.5V AC or 5V DC can be connected to the C1 input through a
>current-limiting resistor where it will be rectified/peak detected." In fact
>it mentions vibrational sensors as a possible input source which is very
>likely to be AC.
>
>So it seems by placing a 1:12.5 step-up transformer from your 200mV input
>you could produce a 2.5V AC signal suitable for use.
>
>Mark.
>

Apparently the internal oscillator is operated at 10-100 kHz, so it
would make sense to optimize the synchronous rectifier for that
frequency range too.

I very much doubt that the synchronous rectifier would be too useful
at 950 MHz, which the OP had in mind.


From: Grant on 25 Jul 2010 21:44
On Sun, 25 Jul 2010 17:07:54 +0100, "markp" <map.nospam(a)f2s.com> wrote:

>>
>> markp wrote:
>>
>> Hey mark, I have already looked at the LTC3108 chip.yes it's used for
>> energy harvesting, but it needs a dc input voltage. I plan to use that
>> chip, but before that I have to rectify my AC voltage.
>>
>
>Not true, the application circuit actually produces an AC source from DC by
>using a resonant oscillator which is then synchronously rectified. The
>device can be used with AC, see page 14: "Any source whose peak voltage
>exceeds 2.5V AC or 5V DC can be connected to the C1 input through a
>current-limiting resistor where it will be rectified/peak detected." In fact
>it mentions vibrational sensors as a possible input source which is very
>likely to be AC.
>
>So it seems by placing a 1:12.5 step-up transformer from your 200mV input
>you could produce a 2.5V AC signal suitable for use.

At 950MHz?

Grant.
>
>Mark.
>
From: Grant on 25 Jul 2010 21:50
On Sun, 25 Jul 2010 09:31:36 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote:

>On Sun, 25 Jul 2010 02:25:32 +0000,
>findprahul_at_yahoo_dot_co_dot_uk(a)foo.com (rahulponna) wrote:
>
>>rahulponna had written this in response to
>>http://www.electrondepot.com/electrodesign/Re-AC-to-DC-conversion-without-using-diodes-and-no-external-484602-.htm
>> :
>>
>>Jamie wrote:
>>
>>I am looking at a frequency of 950MHz. the input voltage is 200mV (peak).
>>Also for precision rectifier I have to use external supply for the op amp.
>>I need to make all my electronics work with the harvested energy.
>>
>>
>[snip]
>
>950MHz is a RFID "TAG" frequency.

!!

When I worked with them they were still down around 130kHz, time
flew. And they self power from the loop field, transmit during
the breaks in loop excitation. Were used back then for cattle,
dog and cat 'chipping'.

Easy to get power transferred 'cos it's a tuned circuit to
known frequency, and fairly short range -- rx inside or close
to loop antenna.

Grant.
>
>What is the source impedance? How about a transmission line
>transformer?
>
> ...Jim Thompson
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