While searching a literature related to my experiment I come across this paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4424026/pdf/PP_PP201500119.pdf . On the page 27 under the section SRS microscopy they have described the set up. The detector used is a thorlabs si-photodiode https://www.thorlabs.com/drawings/5192555af7db78e1-C0DBB61A-E594-6195-A9756D77D1A106F9/FDS1010-SpecSheet.pdf, whose spec says that max reverse bias is 25V. However, in the paper they have said to have it operated under 70 V bias. Am I missing something ? P.S: Question was initially posted on beta engineering but deleted.
Electronic – Can a photodiode tolerate a reverse bias beyond its specification
circuit-designphotodiode
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I'll edit this answer severely as a general comment:
Photodiodes may be operated either forward or reverse biased.
Forward biased gives most output.
Reverse biased gives most speed. and is noisier.
In this mode Vsupply needs to be < Vreversebreakdown - hopefully in the data sheet.
Reverse biased mode is most usually used.
The Sharp BS120 is optimised for 560 nM operation. It specifies Vreverse_abs_max as 10 volts and has curves all the way up (or down) to -10V.
In "forward biased" mode the diode is usually operated with NO added bias and is used as a voltage source.
For a silicon diode with Vforwards = Vf = 0.6V . Say you want 5 mA current and are using a 5V supply then
I = V / R = = (Vsupply - Vdiode) / R = (5-0.6) / 0.005 = 880 ohms Say 1000 Ohms (which gives a notional 4.4 mA)
For 1 mA you'd use (5-0.6)/0.001 = 4400 Ohms
Well, a PWM pin through an RC circuit basically acts like a DAC, so as long as you use a low enough cutoff frequency you should be fine. That being said, the circuit you linked probably needs an external RC filter for the control voltage input. It looks like C8 and C9 are required to reduce output noise by slowing down the response of the converter by limiting the feedback bandwidth. However, feeding a signal with lots of high frequency components (e.g. a PWM signal) directly into the feedback pin will cause issues. So, as long as you add a decent series R and a nice big C right on the Vprogram side of R4, it will probably work just fine.
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Best Answer
The manufacturer gives a maximum voltage that he expects all devices to survive.
When he measures the breakdown voltage in development, he will see a spread due to variations in the manufacturing process and the materials used. The voltage breakdown depends on diffusion depths (difficult to control), defect densities (difficult to control), material purity (difficult to control). So there will be a significant spread of withstand voltages. If he put the maximum at 3 sigma, then he would guarrantee that all his users would experience some failures if they used 1000 devices, which is bad for reputation and business. So he will be more conservative than that.
With a conservative 25v specification, it's easily plausible that some, even most devices of this type, could stand 70v.
The overloaders' creed is 'turn it up until it catches fire, then back off a bit'. If you know what you're doing, in your own one-off experiment, then it's quite a reasonable way of extracting more performance from a cheap stock part. Just don't sell what you've made to unsuspecting 3rd parties, they deserve all components operated within specification.
So if it's for your use, go for it. Just be aware that if you want to build another one later, or repair that one, diodes to that performance may no longer be available. Manufacturers have been known to change their process to tighten spreads, so can leave the published specification as is, while building a cheaper device that still meets the original specification, but now fails your inflated expectation. If it's not too costly, it would be prudent to do a 'one time buy' of all the diodes you'll ever need from this high performing batch, you may never see them again.