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Old 21st December 2012, 05:45 AM   #1261
RNMarsh is offline RNMarsh  United States
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Originally Posted by scott wurcer View Post
Yes indeed, perfect application. I will gladly answer any questions should they arise. I think the Panasonic ones are cheap and widely stocked and easily make enough volts for any Vp.
Pls help us with the design to use it in the 339A. -Thx RNMarsh
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Old 21st December 2012, 01:14 PM   #1262
davada is offline davada  Canada
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Default PV

Scott will these output a proportional voltage to LED current?

The data sheets for the Panasonic says cut off voltage of 8.7 volts.
What does this mean?
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Old 21st December 2012, 01:29 PM   #1263
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Scott will these output a proportional voltage to LED current?

The data sheets for the Panasonic says cut off voltage of 8.7 volts.
What does this mean?
Everyone gets confused. That's the max open circuit voltage OUT of the PV array, these are speced as MOSFET drivers so their VT would have to be less than that.

In this application they look like a current to current converter of 1/1000, 1mA of LED current makes 1ua of PV current. Into 1 Meg this makes a Volt, you are free to flip the polarity because the array is galvanicly isolated. The graph is on the data sheet, there is a max speced by heat in the LED. I'll post a complete circuit today, got too late last night.
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Old 21st December 2012, 01:46 PM   #1264
davada is offline davada  Canada
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Originally Posted by scott wurcer View Post
Everyone gets confused. That's the max open circuit voltage OUT of the PV array, these are speced as MOSFET drivers so their VT would have to be less than that.

In this application they look like a current to current converter of 1/1000, 1mA of LED current makes 1ua of PV current. Into 1 Meg this makes a Volt, you are free to flip the polarity because the array is galvanicly isolated. The graph is on the data sheet, there is a max speced by heat in the LED. I'll post a complete circuit today, got too late last night.
That's great. They are sold as switches so yes I got confused. I thought they were on off devices.

Thanks,
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Old 21st December 2012, 01:47 PM   #1265
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These PV's don't have much of a output voltage range.

3V min and 8V max is typical. Not sure how to use these.
They stack fine but 8V would pinch-off almost any FET I use. I made my own 65V versions on a project chip.
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Old 21st December 2012, 01:49 PM   #1266
davada is offline davada  Canada
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They stack fine but 8V would pinch-off almost any FET I use. I made my own 65V versions on a project chip.
Even a 5 volt would be fine for the 339a osc.
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Old 21st December 2012, 04:05 PM   #1267
1audio is online now 1audio  United States
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Scott-
How fast to the LED-PV links respond? I suspect the PV is a pretty high source impedance so a small cap will slow them down a lot (not bad if you don't have stability problems from it). I can see some other interesting applications for it.
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Old 21st December 2012, 06:36 PM   #1268
RNMarsh is offline RNMarsh  United States
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Default 339A stock Osc ckt -

In case anyone is wondering what happened to ideas about paralleling and Rsource trimming --- I did the parallel using same jFET from another spare unit... used it backwards and forwards. The Rsource trim does find a null but it isnt any deeper than the stock 339A osc with a single jFET. HP had found the sweet-spot with this method. So onward and upward with SW's suggestion. For those following along, I've attached the osc section of the schematic. Thx-RNMarsh
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File Type: jpg 339A osc ckt.jpg (713.7 KB, 137 views)

Last edited by RNMarsh; 21st December 2012 at 06:39 PM.
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Old 21st December 2012, 06:49 PM   #1269
davada is offline davada  Canada
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Scott-
How fast to the LED-PV links respond? I suspect the PV is a pretty high source impedance so a small cap will slow them down a lot (not bad if you don't have stability problems from it). I can see some other interesting applications for it.
Hi Demian,

The guys using these for output protection replacing relays with solid state relays say 100ms to turn off a mosfet. A Jfet has a much lower capacitance.

The PV's can be paralleled for speed up. The manufactures of these PV's make them for SMP applications.

I don't think this should be a problem at least for the 339a osc. Consider the 60uF cap in series with the 2k resistor on the jfet feedback leg.

The circuit Scott proposed replaces the feedback arrangement.

We will see.

Cheers,
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Old 21st December 2012, 07:03 PM   #1270
davada is offline davada  Canada
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Originally Posted by RNMarsh View Post
In case anyone is wondering what happened to ideas about paralleling and Rsource trimming --- I did the parallel using same jFET from another spare unit... used it backwards and forwards. The Rsource trim does find a null but it isnt any deeper than the stock 339A osc with a single jFET. HP had found the sweet-spot with this method. So onward and upward with SW's suggestion. For those following along, I've attached the osc section of the schematic. Thx-RNMarsh
Try it at 10KHz. Found a much better null there than at 1KHz.
I was getting 100dB-110dB on the 2nd at 10KHz and now I get -120dB or there about.
The amplitude control has to be trimmed as well as the Rsource trim.
The two trims have to be worked alternately to get the best null. If you think you have best try going a little further with the trims. Some times the 2nd rises and fall again much deeper.

I have tried it with and without paralleling a few times.

Adding a degeneration R to source, and yes I did cut the trace, had an opposite effect to what was proposed.

I do think we have hit bottom with oscillator. I'm experimenting with larger caps in the AGC filtering and integrator. Too big a cap here kills the oscillator. My target is THD20+N -120db.

A THSH might do better for the AGC. Jfets seem to enjoy a really fast AGC.
Get the ripple down.

Cheers,
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Last edited by davada; 21st December 2012 at 07:20 PM.
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