Hi I am designing a photodiode-amplification circuit. I only have 1 power source (0 - 30V). I was thinking about using 0 and 30V as vee and vcc for my opamp (LM741), and making the photodiode (fds100) signal float on 15V.
Thanks!
For the power source, try using a 7815 (assuming low current as seems to be the case). These are availabvle in a bewildering array of packages from a wide variety of manufacturers and are very inexpensive and easily available.
Cheers
PeteS
I don't think I've ever designed a photodiode circuit, or if I did it was a long time ago. Off hand, I would say that you could use a Zener diode to regulate the voltage.
One way to do that is to make the load as stable as possible. I'm envisioning a circuit in which you have a stable supply voltage, and just connect a voltage divider with equal resistances from "vee" to "vcc". That mid-point voltage then goes to the op amp (+) input, which is low current and reasonably stable. What will you call "ground" in this circuit? How will you "read out" the output? The photodiode can feed current to the op amp (-) input, and a feedback resistor from op amp output to the (-) input will convert that op amp current to a voltage drop, but the output voltage is referenced to the voltage at the (+) input.
If I were doing it with a single supply, since the photodiode current will be in one direction only, I'd get an op amp with low input bias current, and rail-to-rail input (or at least input common mode that includes the negative supply). The op amp should then also have rail-to-rail output or at least output that can go to the negative supply as well. Then the same circuit can reference everything to the negative supply voltage, which you can call ground. If you really need a bias (which would be negative in this case) on the photodiode for what you are doing, you can use a 9V alkaline battery, which will last for the shelf-life of the battery almost certainly, unless you're shining gobs of light on the photodiode all the time.
In any event, the op amp should have input bias current well below the minimum photodiode current you wish to detect. If you're doing low light level work, the 741 is probably not a good choice. Op amps are cheap, and picking the right one can save you a LOT of hassle.
Cheers, Tom
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