Boost photodiode output voltage with transformer?

Thread Starter

icypenguenz

Joined Mar 1, 2011
4
For the design of a no-power light detector, I need to boost the output of a small photodiode array (produces 20mV @ 1uA) to 1.5V. Since a short voltage spike would be sufficient and the light source will be oscillating, shouldn't a transformer be able to do the job? I tried this with a 1:50 turn ratio transformer but didn't observe any additional output at the secondary.
Any help would be greatly appriciated, thanks!
 

K7GUH

Joined Jan 28, 2011
190
Seems like an amplifier circuit would be more appropriate. The photo diode is direct current, is it not? Feeding d.c. into a transformer will get you a spike, but it will be of short duration and not carry much power. The amplifier doesn't have to be very powerful, but the 1.5 volt output has to have sufficient current to operate whatever is hooked to it.
 

Thread Starter

icypenguenz

Joined Mar 1, 2011
4
I am trying to avoid an amp at all cost, but will use it if neccessary. I am using the 1.5V signal to wake up up a microcontroller that is in stand by. The transition from low to high is what the uC is looking for, so short duration shouldnt be a problem.
 

wayneh

Joined Sep 9, 2010
16,398
I am trying to avoid an amp at all cost, but will use it if neccessary. I am using the 1.5V signal to wake up up a microcontroller that is in stand by. The transition from low to high is what the uC is looking for, so short duration shouldnt be a problem.
Why not use a small photocell, say one harvested from a cheap landscape light? It'd give a ton more juice than a photodiode.
 

Papabravo

Joined Feb 24, 2006
13,924
I am trying to avoid an amp at all cost, but will use it if neccessary. I am using the 1.5V signal to wake up up a microcontroller that is in stand by. The transition from low to high is what the uC is looking for, so short duration shouldnt be a problem.
That sounds pennywise and poundfoolish. Whatever the size of the transformer, it HAS to weigh more and consume more board space than an operational amplifier. Have you measured one lately? They're too small for me to see anymore.
 

Thread Starter

icypenguenz

Joined Mar 1, 2011
4
Yes, I know that op-amps are quite good these days. I have one that consumes only 700nA from TI. I am trying to avoid using one since this is a "no-power" application.
 

wayneh

Joined Sep 9, 2010
16,398
Yes, I know that op-amps are quite good these days. I have one that consumes only 700nA from TI. I am trying to avoid using one since this is a "no-power" application.
So far, it's only "no-power" because you say so. You didn't explain why you don't just use a small solar cell. Maybe charge a cap and "ping" a voltage spike if you really need that.
 

Papabravo

Joined Feb 24, 2006
13,924
Yes, I know that op-amps are quite good these days. I have one that consumes only 700nA from TI. I am trying to avoid using one since this is a "no-power" application.
What will you do if the choice is between alternatives that don't solve the problem and one that solves the problem but does not meet your requirements. Not all problems have solutions that meet our requirements. What ever convinced you there was a solution that did?
 

Thread Starter

icypenguenz

Joined Mar 1, 2011
4
You haven't heard about the new line of microcontrollers that break the laws of thermodynamics? The sensor itself needs to be "no-power". This is for a school project and there are several design constraints set by my professor. One is that there can be no external power source and another is that it must be a particular photodiode.

Charging and discharging a cap seems like a good idea. Thank you, I will try that.
 

Kermit2

Joined Feb 5, 2010
4,162
If it were me, I'd tell the instructor I'd be happy with an 'F' for the assignment if he'd let me examine and see, in operation, the one he built


;)
 

beenthere

Joined Apr 20, 2004
15,819
You haven't heard about the new line of microcontrollers that break the laws of thermodynamics? The sensor itself needs to be "no-power". This is for a school project and there are several design constraints set by my professor. One is that there can be no external power source and another is that it must be a particular photodiode.
This sounds pretty absurd. Are you able to give part numbers or references?
 
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