Building a current source that behave like a solar cell?

Thread Starter

MikeJacobs

Joined Dec 7, 2019
215
Anyone have any thought on a simple circuit that would behave the way a solar cell does?

voltage collapse with it shorted
have some open circuit voltage with no load
etc etc just like a solar cell but with a few parts.

Thanks for the ideas
 

LowQCab

Joined Nov 6, 2012
1,614
All of the following Circuits basically do the same thing,
they try to maintain a fixed Voltage-Drop across a very low value Resistor.

When the Voltage being supplied goes up,
the Voltage across the Load continues to go up as well,
until a preset amount of Current is flowing in the Resistor.
If the Current tries to exceed the set amount,
the Voltage across the Load will decrease to keep the Current at the set-point.

The Resistance of the Load generally determines how much
Current will "Attempt" to flow at a given Voltage Input.

A Solar-Cell is not exactly this precise,
they're kinda "mooshy" devices,
but the effect will be very similar.
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Current Regulator 1 .png

Voltage Controlled Current Sink .png

Current Reference 2 .PNG

Current Reference .PNG
 

Thread Starter

MikeJacobs

Joined Dec 7, 2019
215
Are you trying to show a depletion mode mosfet in the first circuit
What does the Schottky do for you
 
Last edited:

LowQCab

Joined Nov 6, 2012
1,614
The lower the Forward-Voltage of the Diode, (in this case 0.3-Volts),
the lower the Voltage-Drop across the Current-Sensing-Resistor will be.
This allows for a much lower Resistance-value to be used,
which may or may not be an advantage.
It's an advantage when a very low Drop-Out-Voltage is a good thing,
like when the Supply-Voltage is barely adequate for the Voltage requirements of the Load.
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Hamlet

Joined Jun 10, 2015
485
I am going to reply to this only so I can find it again. Lots of good stuff here, and the emulation of a solar cell has benchtop applications.
 

Thread Starter

MikeJacobs

Joined Dec 7, 2019
215
The lower the Forward-Voltage of the Diode, (in this case 0.3-Volts),
the lower the Voltage-Drop across the Current-Sensing-Resistor will be.
This allows for a much lower Resistance-value to be used,
which may or may not be an advantage.
It's an advantage when a very low Drop-Out-Voltage is a good thing,
like when the Supply-Voltage is barely adequate for the Voltage requirements of the Load.
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You didn’t answer the question about the fet
I have simulated this circuit and it’s impossible that it works if this is a p channel depletion mode which is the symbol you have produced here
What fet are you intending
 

LowQCab

Joined Nov 6, 2012
1,614
Technically inaccurate Schematic-Symbols are rampant, even in manufacture's Data-Sheets.
Why should I worry about something that You should be smart enough to figure out by now ?
The Schematics that I make are quite often quickly thrown-together, without strict attention to detail.
They are usually to convey a general concept.
Some Schematics that I create are either real-working-Circuits,
with specified values and part-numbers,
others may need extensive simulation and trial-and-error adjustment,
and still others may be so simple that no part-numbers or part-values are given.

Few Circuits work exactly as simulated, almost all need testing and tweaking.

To make things more complex,
it's common for people to substitute specified part-numbers,
and then complain that the Circuit "doesn't-work".

Generally, a Schematic-Symbol is assumed to be the most common part in general use,
unless specifically stated otherwise.
A Depletion-Mode FET is a readily available, but uncommon, item.
"Jelly-Bean" "junk-drawer-parts" will usually work fine in simple Circuits, but certainly not always.

Flip the polarity on the Op-Amp-Inputs to use what ever type of FET You may have on hand.

In order to "guarantee" that a Circuit is going to perform exactly as expected,
You much actually construct the Circuit as it will actually be implemented in the real-World,
and then, test, test, test, test, with an Oscilloscope.
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Thread Starter

MikeJacobs

Joined Dec 7, 2019
215
Technically inaccurate Schematic-Symbols are rampant, even in manufacture's Data-Sheets.
Why should I worry about something that You should be smart enough to figure out by now ?
The Schematics that I make are quite often quickly thrown-together, without strict attention to detail.
They are usually to convey a general concept.
Some Schematics that I create are either real-working-Circuits,
with specified values and part-numbers,
others may need extensive simulation and trial-and-error adjustment,
and still others may be so simple that no part-numbers or part-values are given.

Few Circuits work exactly as simulated, almost all need testing and tweaking.

To make things more complex,
it's common for people to substitute specified part-numbers,
and then complain that the Circuit "doesn't-work".

Generally, a Schematic-Symbol is assumed to be the most common part in general use,
unless specifically stated otherwise.
A Depletion-Mode FET is a readily available, but uncommon, item.
"Jelly-Bean" "junk-drawer-parts" will usually work fine in simple Circuits, but certainly not always.

Flip the polarity on the Op-Amp-Inputs to use what ever type of FET You may have on hand.

In order to "guarantee" that a Circuit is going to perform exactly as expected,
You much actually construct the Circuit as it will actually be implemented in the real-World,
and then, test, test, test, test, with an Oscilloscope.
.
.
.
wow so you make a post with literally the wrong schematic symBol then when I ask for clarification tell me I should just know?
do us all a favor , don’t answer any other questions
If I knew what it was I wouldn’t have to ask.
 

ericgibbs

Joined Jan 29, 2010
14,697
Anyone have any thought on a simple circuit that would behave the way a solar cell does?
Hi Mike,

You could use a LM317 in a fixed current mode.
Do you want about 17Vdc when open circuit, no load, ie: Solar panel range
What short circuit current, at 0V, do you require.
E
 

LowQCab

Joined Nov 6, 2012
1,614
.......... so you make a post with literally the wrong schematic symBol
then when I ask for clarification tell me I should just know ? .........

................. If I knew what it was I wouldn’t have to ask.

Have You actually proof-read your post ?

How do You know that the Schematic-Symbol used is wrong ?

A poor Schematic would be one where a specific-part is required for the Circuit to perform as expected,
but yet the special-part is not specified, in writing, by number, or at least by "family" or type.
For example,
a "6uf" Capacitor could be any one of at least 4 different types,
all of which have substantially different characteristics and interactions in a particular Circuit.

Your Post-Title says You want to "build" a Circuit.
So it might be easily assumed that You are competent at
reading Schematics, and building elementary Circuits,
and having a basic understanding of how basic Electronic-Components work.
If my assumption was misplaced, I apologize,
but there is no need to loose your cool and start making rude accusations.

You received 4 examples of Circuits that may do what You need, for free.
No one owes anyone else here anything, for any reason.
You should feel grateful that there are so many good, smart people here
willing to help You out, for free.
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