On a sunny day (Fri, 03 Nov 2023 12:19:20 -0700) it happened john larkin
<jl@650pot.com> wrote in <7ugakit1jtm431b4jaml3cs43gla1amdi8@4ax.com>:

>On Fri, 3 Nov 2023 09:47:09 -0700 (PDT), Fred Bloggs
><bloggs.fredbloggs.fred@gmail.com> wrote:
>
>>On Friday, November 3, 2023 at 11:02:35?AM UTC-4, John Larkin wrote:
>>> I have an opamp with a 10 volt positive supply and need the output to 
>>> swing to about 16 volts. I was thinking I could add a paralleled 6.8 
>>> volt zener, a cap, and a floating power supply at the opamp output. 
>>> 
>>> The power supply could be a PV optocoupler like this: 
>>> 
>>> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804 
>>> 
>>> My load is obviously light, a varicap in fact.

If you want to tune a 50 MHz? oscillator with a varicap,
I tune those with a transistor Cce,
here tuning a crystal oscillator, 25 MHz f0, pot on the left.
 https://panteltje.nl/pub/lnb_ref_circuit_update_IMG_6652.JPG
No need for high voltages, pick a low capacitance NPN or PNP if frequencies are very high.

On a sunny day (Fri, 03 Nov 2023 08:01:58 -0700) it happened John Larkin
<jl@997PotHill.com> wrote in <db2aki9v2gst0o57hamemq56brv7vscdol@4ax.com>:

>I have an opamp with a 10 volt positive supply and need the output to
>swing to about 16 volts. I was thinking I could add a paralleled 6.8
>volt zener, a cap, and a floating power supply at the opamp output.
>
>The power supply could be a PV optocoupler like this:
>
>https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804
>
>My load is obviously light, a varicap in fact.

Interesting, you get about 8 V at 10 mA and 1 M load.

On Friday, November 3, 2023 at 8:02:35 AM UTC-7, John Larkin wrote:
> I have an opamp with a 10 volt positive supply and need the output to 
> swing to about 16 volts. I was thinking I could add a paralleled 6.8 
> volt zener, a cap, and a floating power supply at the opamp output. 
> 
> The power supply could be a PV optocoupler like this: 
> 
> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804 
> 
> My load is obviously light, a varicap in fact.
So, put two lithium coin cells in series with the op amp output (it'll work for years if the load is really light).

Zeners sound good until you actually see one with very light current through it; they can be unstable and noisy.

On Fri, 3 Nov 2023 19:29:46 +0000, piglet <erichpwagner@hotmail.com>
wrote:

>On 03/11/2023 19:19, john larkin wrote:
>> On Fri, 3 Nov 2023 09:47:09 -0700 (PDT), Fred Bloggs
>> <bloggs.fredbloggs.fred@gmail.com> wrote:
>> 
>>> On Friday, November 3, 2023 at 11:02:35?AM UTC-4, John Larkin wrote:
>>>> I have an opamp with a 10 volt positive supply and need the output to
>>>> swing to about 16 volts. I was thinking I could add a paralleled 6.8
>>>> volt zener, a cap, and a floating power supply at the opamp output.
>>>>
>>>> The power supply could be a PV optocoupler like this:
>>>>
>>>> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804
>>>>
>>>> My load is obviously light, a varicap in fact.
>>>
>>> Not seeing the need for a zener...
>> 
>> The PV voltage has a bad negative tempco, and that could cause us
>> problems. A zener helps that. An LM4040 bandgap would be great, but
>> they only come in 5 and 10 volts, too low and too high!
>>>
>>> I take it mean the standard non-inverting OA with the PV in series with OA output, and a high-Z resistor feedback divider from the composite output (PV cathode) to OA (-). Loop gain, which should be very large attenuates noise and the unknowns at the composite output.
>> 
>> If I have a pretty constant offset added to the opamp output, I don't
>> need to feed back from the offset,  just from the opamp output. If I
>> use the PV for the offset, I don't have enough current for the opampm
>> feedback resistor.
>>>
>>> Is there some reason you can't drive current through the detector? Maybe too non-linearizing...
>>>
>>> They datasheet is so fixed on detector Voc Isc with input LED drive, it's almost tempting to use the LED drive to modulate the final output into place.
>> 
>> To slow.
>> 
>> Nice puzzle.
>> 
>
>There is the adjustable LM4041 but the minimum operating current will be 
>too much for the PV.
>
>Most action in a varicap is in the 1-10V range, can't you simply pad the 
>varicap capacitance down so you avoid the need to go to 16V?
>
>piglet

The varicap is violently nonlinear at low voltages. Something like 6
to 18 volts has about a 2:1 slope, which we can barely tolerate. Maybe
I can talk the boys into doing a 2nd order polynomial in the FPGA to
correct the varicap curve and keep the control loop happier.

But today's revelation is to bias the cold side of the varicap to -8V,
and not grounding it, instead of shifting the opamp output up!

On Friday, November 3, 2023 at 3:19:36 PM UTC-4, john larkin wrote:
> On Fri, 3 Nov 2023 09:47:09 -0700 (PDT), Fred Bloggs 
> <bloggs.fred...@gmail.com> wrote:
> >On Friday, November 3, 2023 at 11:02:35?AM UTC-4, John Larkin wrote: 
> >> I have an opamp with a 10 volt positive supply and need the output to 
> >> swing to about 16 volts. I was thinking I could add a paralleled 6.8 
> >> volt zener, a cap, and a floating power supply at the opamp output. 
> >> 
> >> The power supply could be a PV optocoupler like this: 
> >> 
> >> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804 
> >> 
> >> My load is obviously light, a varicap in fact. 
> > 
> >Not seeing the need for a zener...
> The PV voltage has a bad negative tempco, and that could cause us 
> problems. A zener helps that. An LM4040 bandgap would be great, but 
> they only come in 5 and 10 volts, too low and too high!
> > 
> >I take it mean the standard non-inverting OA with the PV in series with OA output, and a high-Z resistor feedback divider from the composite output (PV cathode) to OA (-). Loop gain, which should be very large attenuates noise and the unknowns at the composite output.
> If I have a pretty constant offset added to the opamp output, I don't 
> need to feed back from the offset, just from the opamp output. If I 
> use the PV for the offset, I don't have enough current for the opampm 
> feedback resistor.

Did you say you have unregulated 24VDC? Then just find an OA that can handle it and use that to buffer the feedback resistor divider.

> > 
> >Is there some reason you can't drive current through the detector? Maybe too non-linearizing... 
> > 
> >They datasheet is so fixed on detector Voc Isc with input LED drive, it's almost tempting to use the LED drive to modulate the final output into place.
> To slow. 
> 
> Nice puzzle.

On Friday, November 3, 2023 at 3:19:36 PM UTC-4, john larkin wrote:
> On Fri, 3 Nov 2023 09:47:09 -0700 (PDT), Fred Bloggs 
> <bloggs.fred...@gmail.com> wrote:
> >On Friday, November 3, 2023 at 11:02:35?AM UTC-4, John Larkin wrote: 
> >> I have an opamp with a 10 volt positive supply and need the output to 
> >> swing to about 16 volts. I was thinking I could add a paralleled 6.8 
> >> volt zener, a cap, and a floating power supply at the opamp output. 
> >> 
> >> The power supply could be a PV optocoupler like this: 
> >> 
> >> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804 
> >> 
> >> My load is obviously light, a varicap in fact. 
> > 
> >Not seeing the need for a zener...
> The PV voltage has a bad negative tempco, and that could cause us 
> problems. A zener helps that. An LM4040 bandgap would be great, but 
> they only come in 5 and 10 volts, too low and too high!
> > 
> >I take it mean the standard non-inverting OA with the PV in series with OA output, and a high-Z resistor feedback divider from the composite output (PV cathode) to OA (-). Loop gain, which should be very large attenuates noise and the unknowns at the composite output.
> If I have a pretty constant offset added to the opamp output, I don't 
> need to feed back from the offset, just from the opamp output. If I 
> use the PV for the offset, I don't have enough current for the opampm 
> feedback resistor.

You do if you bootstrap a buffer into the feedback divider.

This example looks simplified:

https://www.digikey.com/en/articles/how-to-solve-analog-high-voltage-delivery-challenges

This approach is complicated and parts intensive, but the author is an IC designer so number of parts don't matter:

https://www.analog.com/en/analog-dialogue/raqs/raq-issue-168.html

The bootstrapped buffer drives the resistor divider feedback to the first OA.

> > 
> >Is there some reason you can't drive current through the detector? Maybe too non-linearizing... 
> > 
> >They datasheet is so fixed on detector Voc Isc with input LED drive, it's almost tempting to use the LED drive to modulate the final output into place.
> To slow. 
> 
> Nice puzzle.

On Friday, November 3, 2023 at 3:17:48 PM UTC-4, piglet wrote:
> On 03/11/2023 16:47, Fred Bloggs wrote: 
> > On Friday, November 3, 2023 at 11:02:35 AM UTC-4, John Larkin wrote: 
> >> I have an opamp with a 10 volt positive supply and need the output to 
> >> swing to about 16 volts. I was thinking I could add a paralleled 6.8 
> >> volt zener, a cap, and a floating power supply at the opamp output. 
> >> 
> >> The power supply could be a PV optocoupler like this: 
> >> 
> >> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804 
> >> 
> >> My load is obviously light, a varicap in fact. 
> > 
> > Not seeing the need for a zener... 
> > 
> > I take it mean the standard non-inverting OA with the PV in series with OA output, and a high-Z resistor feedback divider from the composite output (PV cathode) to OA (-). Loop gain, which should be very large attenuates noise and the unknowns at the composite output. 
> > 
> > Is there some reason you can't drive current through the detector? Maybe too non-linearizing... 
> > 
> > They datasheet is so fixed on detector Voc Isc with input LED drive, it's almost tempting to use the LED drive to modulate the final output into place.
> Not clear to me from JL's original post if the op amp has a negative 
> supply rail so that even after the 7V output offset the varicap can be 
> biased below 7V? 

Good point. Shunt the PV with an anti-parallel diode.

> 
> Modulating the PV LED drive could have horrible delays and upset the 
> dynamics? 
> 
> piglet

On 03/11/2023 19:19, john larkin wrote:
> On Fri, 3 Nov 2023 09:47:09 -0700 (PDT), Fred Bloggs
> <bloggs.fredbloggs.fred@gmail.com> wrote:
> 
>> On Friday, November 3, 2023 at 11:02:35?AM UTC-4, John Larkin wrote:
>>> I have an opamp with a 10 volt positive supply and need the output to
>>> swing to about 16 volts. I was thinking I could add a paralleled 6.8
>>> volt zener, a cap, and a floating power supply at the opamp output.
>>>
>>> The power supply could be a PV optocoupler like this:
>>>
>>> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804
>>>
>>> My load is obviously light, a varicap in fact.
>>
>> Not seeing the need for a zener...
> 
> The PV voltage has a bad negative tempco, and that could cause us
> problems. A zener helps that. An LM4040 bandgap would be great, but
> they only come in 5 and 10 volts, too low and too high!
>>
>> I take it mean the standard non-inverting OA with the PV in series with OA output, and a high-Z resistor feedback divider from the composite output (PV cathode) to OA (-). Loop gain, which should be very large attenuates noise and the unknowns at the composite output.
> 
> If I have a pretty constant offset added to the opamp output, I don't
> need to feed back from the offset,  just from the opamp output. If I
> use the PV for the offset, I don't have enough current for the opampm
> feedback resistor.
>>
>> Is there some reason you can't drive current through the detector? Maybe too non-linearizing...
>>
>> They datasheet is so fixed on detector Voc Isc with input LED drive, it's almost tempting to use the LED drive to modulate the final output into place.
> 
> To slow.
> 
> Nice puzzle.
> 

There is the adjustable LM4041 but the minimum operating current will be 
too much for the PV.

Most action in a varicap is in the 1-10V range, can't you simply pad the 
varicap capacitance down so you avoid the need to go to 16V?

piglet

On Fri, 3 Nov 2023 09:47:09 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

>On Friday, November 3, 2023 at 11:02:35?AM UTC-4, John Larkin wrote:
>> I have an opamp with a 10 volt positive supply and need the output to 
>> swing to about 16 volts. I was thinking I could add a paralleled 6.8 
>> volt zener, a cap, and a floating power supply at the opamp output. 
>> 
>> The power supply could be a PV optocoupler like this: 
>> 
>> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804 
>> 
>> My load is obviously light, a varicap in fact.
>
>Not seeing the need for a zener...

The PV voltage has a bad negative tempco, and that could cause us
problems. A zener helps that. An LM4040 bandgap would be great, but
they only come in 5 and 10 volts, too low and too high!
>
>I take it mean the standard non-inverting OA with the PV in series with OA output, and a high-Z resistor feedback divider from the composite output (PV cathode) to OA (-). Loop gain, which should be very large attenuates noise and the unknowns at the composite output.

If I have a pretty constant offset added to the opamp output, I don't
need to feed back from the offset,  just from the opamp output. If I
use the PV for the offset, I don't have enough current for the opampm
feedback resistor.
>
>Is there some reason you can't drive current through the detector? Maybe too non-linearizing...
>
>They datasheet is so fixed on detector Voc Isc with input LED drive, it's almost tempting to use the LED drive to modulate the final output into place.

To slow.

Nice puzzle.

On 03/11/2023 16:47, Fred Bloggs wrote:
> On Friday, November 3, 2023 at 11:02:35 AM UTC-4, John Larkin wrote:
>> I have an opamp with a 10 volt positive supply and need the output to
>> swing to about 16 volts. I was thinking I could add a paralleled 6.8
>> volt zener, a cap, and a floating power supply at the opamp output.
>>
>> The power supply could be a PV optocoupler like this:
>>
>> https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP3905-TPR-E/7809804
>>
>> My load is obviously light, a varicap in fact.
> 
> Not seeing the need for a zener...
> 
> I take it mean the standard non-inverting OA with the PV in series with OA output, and a high-Z resistor feedback divider from the composite output (PV cathode) to OA (-). Loop gain, which should be very large attenuates noise and the unknowns at the composite output.
> 
> Is there some reason you can't drive current through the detector? Maybe too non-linearizing...
> 
> They datasheet is so fixed on detector Voc Isc with input LED drive, it's almost tempting to use the LED drive to modulate the final output into place.

Not clear to me from JL's original post if the op amp has a negative 
supply rail so that even after the 7V output offset the varicap can be 
biased below 7V?

Modulating the PV LED drive could have horrible delays and upset the 
dynamics?

piglet