maybe the diode will produce even more current

Reverse biased photodiode do not produce current at all.
When it is connected in series between voltage source and load,
photodiode works as light controlled current limiter only.

 

Reverse biased photodiode do not produce current at all.
When it is connected in series between voltage source and load,
photodiode works as light controlled current limiter only.

Okey.
But how about this post ?

As has been said, there is a limit on the actual current that will be output. For a photodiode that's intended to work in reverse-biassed or zero-bias configurations that limit will be at around 1mW/cm2 or 10W/m2 which is why data sheets generally only show values up to that point. 10W/m2 is typically medium to bright indoor lighting (1000W/m2 is generally taken as the maximum irradiation from the sun overhead on a cloudless day, and is used for solar panels and other true photovoltaic cells).

You can think of a photodiode as a perfect diode in parallel with a current source and a parallel load resistor Rp, plus a series resistor Rs to the external connection. The current source is linear with respect to the light power up to a certain limit but can't go above that (there only being so many electrons in the depletion layer that can be freed). The current source biasses the diode in the forward direction. Once the diode is starts conducting the current mainly flows through it giving an output voltage of typically 0.4-0.6v; when the output is shorted the photocurrent flows externally and the voltage is near to zero. These two states are illustrated in the simulation below:

View attachment 272487

The following simulations show what happens when the diode is is nominally reverse-biassed, but with different load resistances, RL < RLmax, RL = RLmax and RL > RLmax. In the middle case the diode just remains reverse or zero-biassed at max illumination, while last shows the diode going into forward-bias at high illumination.

View attachment 272488

It says that is is now in forward bias, and it's still photodetector ?

 

A photodiode is always a detector whether leaking or generating current - its still responding to light stimulus - however the speed of response in photoconductive mode (reverse or zero bias) is much faster than in photovoltaic mode (nS v potentially tens of mS). A photodiode for beam interruption sensing is never intended for use in a photovoltaic mode and would never be used as such - indeed if it strayed into that territory it would be considered very poor circuit design.

A photovoltaic cell, intended for power generation, while working on the same basic physical principles, has a completely different physical construction and consists of many series/parallel diode junctions over a much larger area. It would be a completely useless photoconductor.

The scenario you postulated has no practical use AFAIK, so there is no point to further discussion.

 

A photovoltaic cell, intended for power generation, while working on the same basic physical principles, has a completely different physical construction and consists of many series/parallel diode junctions over a much larger area. It would be a completely useless photoconductor.

I mean the basics I know for photodiode to work as photovoltaic cell is that there can't be a voltage source.
Something like this :



But hearing that photovoltaic cell can be a photoconductor is pretty wierd for me.

A photodiode is always a detector whether leaking or generating current - its still responding to light stimulus - however the speed of response in photoconductive mode (reverse or zero bias) is much faster than in photovoltaic mode (nS v potentially tens of mS). A photodiode for beam interruption sensing is never intended for use in a photovoltaic mode and would never be used as such - indeed if it strayed into that territory it would be considered very poor circuit design.

Yes but I just asked a simple question which is : For RL > RLmax it is changing into forward bias. So is this still photoconductive mode ? Or is it changing into photovoltaic. If it's still photoconductive then say yes.

 

Its moving to photovoltaic as the photocurrent is now over-riding the external bias current and the diode pn junction becomes, in this simulation, forward-biassed at around 7.5W/m2..

 

So it is photovoltaic even if there is Voltage source. Because the only photovoltaic I know are those where there is no Voltage source
Is it because I have crossed this limit Ub/RL?

 

I'm sorry for being so persistent.
But this topic is pretty complicated. I was just curious if I give more light while having Ub/RL if something will happen and I read here that if I give more light it still be Ub/RL. And from you I hear that It will change into photovoltaic so I'm confused.
Sorry

 

The only difference is how you perceive it. Light hitting the diode generates photocurrent. If there's an external source holding the device reverse-biassed then that photocurrent is seen as leakage. If not, then its seen as generative... Its only the transition that seems to be confusing you.

 

The only difference is how you perceive it. Light hitting the diode generates photocurrent. If there's an external source holding the device reverse-biassed then that photocurrent is seen as leakage. If not, then its seen as generative... Its only the transition that seems to be confusing you.

But I know only photovoltaic cells that there is no external source.
So it can still be photovoltaic if I add external source ?

Because in this situation :



It is photovoltaic which is wierd for me.

And again sorry for being a little bit annoying

 

If I have a battery connected to a resistor network and I add another battery and resistor network to it, does the first battery stop being a battery?

If I connect a photovoltaic cell to a circuit with a battery, does it stop being photovoltaic? Of course not! If the voltage seen by the photovoltaic cell from the network is greater than the cell voltage it wont export current to the network, but its still photovoltaic.

 

If I have a battery connected to a resistor network and I add another battery and resistor network to it, does the first battery stop being a battery?

If I connect a photovoltaic cell to a circuit with a battery, does it stop being photovoltaic? Of course not! If the voltage seen by the photovoltaic cell from the network is greater than the cell voltage it wont export current to the network, but its still photovoltaic.

I mean you are probably right, I just said what I have seen on the internet that every photowoltaic circuits didn't consist additional voltage source. So I thought that If I want a photodiod to work as a photovoltaic I need it to be connected to the load without this additional voltage but if I want a typical photoconductor I need an additional voltage.

It is pretty wierd for me because it is new that I can change photoconduction into photovoltaic and as I understand I can change it not from light intensity but from this load RL ?

 

I have seen on the internet that every photowoltaic circuits didn't consist additional voltage source

Of course not, since generally you power something from solar power - or recharge a battery - but you won't see something where a battery is 'powering' a solar cell as it has no practical value.

I can change photoconduction into photovoltaic and as I understand I can change it not from light intensity but from this load RL ?

No, that's not the point of what I've demonstrated. A bad choice of RL will potentially drop the diode out of reverse-biassing and that could impact the potential of the circuit to operate reliably. But you wouldn't do that deliberately, there's no practical use AFAIK. And anyway a photodiode for use in an encoder or beam interruptor is a very poor photovoltaic generator, at best a few tens of uA at <1v is of little real use.

 

Of course not, since generally you power something from solar power - or recharge a battery - but you won't see something where a battery is 'powering' a solar cell as it has no practical value.


No, that's not the point of what I've demonstrated. A bad choice of RL will potentially drop the diode out of reverse-biassing and that could impact the potential of the circuit to operate reliably. But you wouldn't do that deliberately, there's no practical use AFAIK. And anyway a photodiode for use in an encoder or beam interruptor is a very poor photovoltaic generator, at best a few tens of uA at <1v is of little real use.

I meant from RL is that wrong choice of RL will make Photoconductor into Photovoltaic. But Photovoltaic with additional battery is a poor photovoltaic as you said.

Beucase As far as I know from this post :

When you cross Ub/RL, current through photodiode is maximal.
When you give more light, current still equal Ub/RL. Photodiode is saturated.

The more light I give the current is still the same it is Ub/RL.

So I thought that if not the light can change this mode from photoconductor to photovoltaic then maybe RL ?

 

So I thought that if not the light can change this mode from photoconductor to photovoltaic then maybe RL ?

ADDED:

So it is RL ?
Because I don't understand the diagrams you have sent here.
What does it show?
As I see is that if the light intensity is high then Vout on photodiode is close to 0 V ? So what does it show for R = 100k ? What does it show ?

TROLL???

 

So it is RL ?
Because I don't understand the diagrams you have sent here.

What does it show?


As I see is that if the light intensity is high then Vout on photodiode is close to 0 V ? So what does it show for R = 100k ? What does it show ?

 

TROLL???

No I really don't understand.
I only see that the voltage drops to zero at some point.
What does it show if you could tell me ? Where does it show that photoconductor changes into photovoltaic ? If that's the point of this diagram.

 

Where does it show that photoconductor changes into photovoltaic ? If that's the point of this diagram.

ADDED:

Ok so If I change the R into like 100 ohm will there be still photovoltaic mode ?

Exactly TROLL.

ADDED:

Ok so If I change the R into like 100 ohm will there be still photovoltaic mode ?

Diagram for RL = 100 Ω:

 

Ok so If I change the R into like 100 ohm will there be still photovoltaic mode ?

Because you said that if there is Ub/RL then more light won't change it and it will be still Ub/RL, so it means that it is still remains in photoconductor mode ?

 

Or am I again wrong ?

 

Exactly TROLL.

????

You have showed that for a certain light there will be photovoltaic mode.
And I was thinking if for 100 ohm there will be also a transition from photoconduction into photovoltaic.

Because all I know from your post from before is that when I have Ub/RL and give more light then it will be still Ub/RL so I was thinking if it's still photoconduction.