High impedence/low impedence circuit using photodiode and transistor

Thread Starter

Kram724

Joined Jan 30, 2014
6
Trying to build a circuit that will give nearly zero ohms when photodiode is open and high ohms when the light hits the diode.
I'm using a photodiode and an npn transistor. +5 Volts is the source. I have had success making the circuit work, but it requires more light than I'm able to give it in the system. Basically I need a way to increase the sensitivity of the P-diode.

Thanks!
 

Bordodynov

Joined May 20, 2015
2,890
What question, such and answer.I showed the idea of increasing the sensitivity: it is using a resistor with a larger value (1MΩ).From such a resistor, the MOS transistor or Darlington will work well.You wanted a small impedance - get (15mΩ).A 1 ohm resistor in the load is to show how low the resistance of an open transistor is.More accurately form your wishes.After all, even a good telepath can not read your thoughts on the distance separating us.
 

Thread Starter

Kram724

Joined Jan 30, 2014
6
Thanks to all. My circuit is very close to the one Bordodynov thankfully submitted, except that I used a 2N2222 transistor. Sorry I didn't give an example, I will work on using the tools here. Also I deleted r2 for an open collector circuit. The objective is to not have any voltage leaving the circuit. Basically an open/close switch. As I increase the resistance in r1 the P-diode does seem to get more sensitive, but there is a limit. I need to activate it with a 400um fiber, which is a very small beam of light. Maybe I need to try a smaller P-diode.

Thanks again!
.
 

Bordodynov

Joined May 20, 2015
2,890
In the place of one transistor include two according to the Darlington scheme. Then you can increase the load resistance of the photodiode. The sensitivity is proportional to the value of the resistor.
 

Colin55

Joined Aug 27, 2015
519
What do you expect a Darling ton to do, over a 2N2222 transistor?

To start with, you are jumping the gun.

The first questions you should ask is: What is the value of the load resistor for the BPW34S, to obtain the greatest sensitivity?
Then ask: Is the change gradual or rapid.
 

Bordodynov

Joined May 20, 2015
2,890
I do not understand why you do not understand my proposals. The maximum value of the resistor is determined by the dark current of the photodiode. In order to work with a large value of the load resistor, it is necessary to have a small input current of the amplifying element. So I immediately suggested using MOS transistor. And further. If you want to get a more specific answer, then you must correctly formulate your goal. For example, what do you want to get at the output, what is the load, what speed is needed. Why do not you use proven solutions? Perhaps you want to solve a complex problem by simple means (because of ignorance of the technology in the field of photodetectors). I was developing a circuit, the sensitivity of which was somewhat picoAmpere photocurrent. I also developed a circuit that records 10 nanosecond pulses. So I could help you, but you're stuck.
 

Colin55

Joined Aug 27, 2015
519
"It would be more useful to the TS if you posted a solution to his problem,"

You obviously don't know what you are talking about.
I have already requested to the first two requirements.
 

ericgibbs

Joined Jan 29, 2010
13,242
Trying to build a circuit that will give nearly zero ohms when photodiode is open and high ohms when the light hits the diode.
I'm using a photodiode and an npn transistor. +5 Volts is the source. I have had success making the circuit work, but it requires more light than I'm able to give it in the system. Basically I need a way to increase the sensitivity of the P-diode.
Above is the TS' posted problem.

@colin
You were simply requested as follows: It would be more useful to the TS if you posted a solution to his problem.

If you cannot make a useful contribution to this Thread, leave it to other members who are prepared to put some effort in helping the TS.
 

Bordodynov

Joined May 20, 2015
2,890
Colin55.
So explain to the dark (ie me) what I need. I have 40 years experience in electronics and I have developed many different schemes (which have worked and work successfully). My specialty is radiophysicist. I developed microcircuits for 20 years (digital and analog). And who are you?
 

Colin55

Joined Aug 27, 2015
519
You need to have a BPW34S and work out what load resistor is required to get the maximum output for the conditions.
You don't know what background illumination is occurring and the intensity of the light from the fibre.
Only after the results are provided can the next step be done.
 

Bordodynov

Joined May 20, 2015
2,890
I used this photodiode because I did not know that the source of radiation is an optical fiber. For an optical fiber, a photodiode with a smaller area should be used. I have a universal spice-model of the photodiode and I can simulate everything. From background illumination in this case, you can get rid by placing the photodiode and the end of the light guide into the housing (box). To obtain high performance, it is necessary to use a transimpedance amplifier. But the author of the post is silent. Maybe he lost interest in the topic?
 
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