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Description: The CPC1822 is a monolithic photovoltaic string of solar cells. When operating in sunlight or a bright artificial light environment the optical energy will activate the cell array and generate a voltage at the output. The solar cells are capable of generating a floating source voltage and current sufficient to drive and power CMOS ICs, logic gates and/or provide "trickle charge" for power applications.

Features:

  • 4V output
  • Works best with natural sunlight
  • Provides true wireless power
  • No EMI/RFI generation
  • Solid state reliability
  • Small 8-pin surface mount SOIC

Documents:

Comments 33 comments

  • (cont)
    I think the only real “work” a person is going to get out of this solar cell is enough power to drive a MOSFET, maybe a small 4000-series chip, maybe a PIC or AVR running on a 32Khz crystal. That’s about it.
    Trickle charge a small battery? Even the smallest LiPo battery sold here, at 20mAh, in a perfect world, with perfect physics, with perfect light, with zero losses in the wiring, with a perfect battery, would take an absolute bare minimum of 400 hours (16 2/3 days) in continuous bright light to charge it up completely (ignoring all the complicated math that goes with charging and discharging).
    I think I’ll go buy a Shamwow!
    JDG

    • You are correct, in every way. People should really look over the datasheet and realize you can’t just plop this in and drive a circuit with it. It has its uses for sure, but isn’t magic.
      Let me know how the shamwow treats ya. ;-)

  • I was thinking about packing several of these on a board, focusing a lens in front of them and polling them to make really crude pictures that I could process with a microcontroller.

  • You could use these micro solar cells as active sensors. Since they generate their own power they would not have to be powered off the controller. I fly quad rotor RC models with lighting on them for show. During the day one of these on a load switch would keep the lights off. In the absence of ambient light the lights would be switched on. Seeing as electric RC models run on batteries, having something that doesn’t draw off current would be a plus. There’s a board on here somewhere that has opto isolators that gate some mosfet switches. One of these could drive the led in the opto isolator. Hmmm

  • These would be cool for projects such as heliostats, where you want to track maximum power. You could use a grid of them (say 5) at slightly different angles to work out the angle that is perpendicular to the suns rays…

  • This minature solar cell worked well for driving a couple of mosfet logic level gates, using only a hi-brightness red led. You don’t get much extra power, just enough voltage across a 1 Meg resistor to operate the gate. Previously, i tried the old “red led as a voltage generator” idea, but while that got 2.1 volts in sunshine, it wasn’t enough to activate the mosfet with only another red led as light source.

  • The application note states that it requires a MOSFET for it to work in a recharging circuit. Can anyone (esp Sparkfun) help or link me to a source for this MOSFET or any alternatives as diodes will be too costly a waste of power, according to the app note. Thanks!!!

    • I’m not fully sure what type of charging you want to do but this site used one of these, a 0.33F supercap and and a diode for reverse voltage protection to charge the supercap to 3.9V with a a fair mA output.

  • Can I use this to charge a 3.7v coin cell?
    http://www.sparkfun.com/products/10319
    My guess would be that the drop from 4v open will result in a voltage that is too low for charging? Then again I could use several of them in series and in parallel to boost voltage and current?

    • Yes they could, however the sheer number needed in parallel to charge that battery would be very impratical.

  • can these be tied to gether to mak eup to a 12 or 18v feed?

    • Theoretically, if tied in series the would supply 12 or 18V, at 50uA, to use these for any practical purposes you would need to use hundreds in parallel to get even a few mA’s.

  • It may not “trickle charge” a battery, but it will do something analogous with many microcontrollers. For example, the MSP430G2231 (one of two microcontrollers in the $4.30 TI Launchpad Kit) draws 220uA@2.2V in Active Mode at 1 Mhz, but only 0.5uA in standby. In some monitoring applications, the microcontroller is mostly in standby, but wakes up every second, minute or hour to check a measurement, then goes back to sleep, resulting in a very low average consumption. One of these, charging an ultracap 8 hrs a day might maintain sufficient charge to run the uC as well as sufficient surplus to trigger an alarm signal if the monitored condition goes out of bounds. I’ve also been working with the Linear Technologies LTC3108, to turn low power sources into usable ones.

  • Is the datasheet correct in indicating that the internal “diodes” are aligned with the conventional current flow, not against it? If so, wouldn’t it be pretty difficult to use these to “trickle charge” a battery?
    (“Trickle charge” always seems to be in quotes, so I’m wondering if it can really trickle charge anything, or if those words imply something else, like some sort of “simulated” trickle charge.)

    • It depends, a “battery” would entitle many, many days of charging in full sun for a fair charge, a super capacitor could charge in a few hours.

  • 4v 50Ua so how many to run an led under room lighting? also maybe use a capacitor and get at least a blink out of an led?

    • Hooked up in parallel, 200 of these in perfect conditions could run a very little, low power Led, with a capacitor maybe a few hours of sun for a couple of minutes at a time, these are not designed for -all things being relative- high current applications.

  • No this will not power a robot but if it produces 50ua in sunlight at 4V that is enough to charge a supercap that can then run some low power micros like the MSP430 from ti or the PIC16F1827.
    1 MSP430
    1 supercap
    1 cpc1822
    They all can fit on a 1 inch square pc board and you have a working sun powered micro.

  • For the price, you could always string together 10 or 20 of these at varying angles :P

  • Combined with a 0.33F supercap, you can get a full charge (3.9v) in one day. http://dorkbotpdx.org/blog/laen/an_itty_bitty_power_provider
    With that power, you can run a 10mA LED for 1 minute. Or power an ATtiny at 32KHz in Idle 24/7 and wake up to take measurements several times a day.
    Yes, you need to be very careful about power saving modes and leakage.
    No, it will not charge your LiPo minty-boost.

  • I’ve seen these used with a super cap to drive an underclocked pic for a couple mins a day. May be useful in a simple outdoor logging application. Something like logging soil moisture or daily sunlight measurements.

  • People aren’t reading the datasheet correctly.
    Open circuit maximum voltage output = 4v
    Open circuit means zero current flow. Put a load on it and the voltage will drop off dramatically. If you’ve got maximum voltage, but can’t support any current flow, you can’t do any work.
    Short circuit maximum current output = 50 uA
    Again, short circuit means maximum current flow with little or no voltage behind it (hence the term short circuit). If you’ve got maximum current flow, but no voltage behind it, can’t do any work.
    What this datasheet doesn’t have is a voltage over current graph, which will show the ‘knee’ of the curve, which would be the optimal region to operate this solar cell.
    Ya can’t have an open circuit and a short circuit at the same time.
    Also, note in the description in the datasheet:
    The CPC1822 is a monolithic photovoltaic string of solar cells with switching circuitry. When operating in sunlight or a bright artificial light environment the optical energy will activate the cell array and generate a voltage at the output. The solar cells are capable of generating a floating source voltage and current sufficient to drive and power CMOS ICs, logic gates and/or provide ?trickle charge? for battery applications.
    (cont)

  • There is no switcher, this is a raw solar cell which is effectively a stack of diodes. It will output a voltage relative to the amount of light. Noon-day summer sun I got about 4.2 volts open circuit. Indoors at 5pm indirect light 2 volts. Night indoor lighting 0.4 volts.

    • Hi gpeek,
      You are correct and the datasheet is incorrect. There is NOT “switching circuitry”, as the datasheet puts it, within these solar cells. I will be sure to update the doc when the new one becomes available.
      Thanks for catching that!

  • Why would you need this? Too little current… and even if you boost the current, will you have enough voltage to drive anything?

    • These are primarily used alone as trickle chargers for batteries, see app note for reference.

  • So am I correct in thinking that this will give about 4V or nothing. When the light intensity reaches a threshold it’ll start outputting 4V but it will stay at zero for any light below that threshold? Is this the “switching circuitry” mentioned?

    • Yes, that is correct. For you to get close to the 50uA spec at 4V, you will need to be in view of sunlight or a really intense lamp. The solar cell will not trigger to 4V with ordinary room light.

    • I’m wondering the same thing. At first I tought these devices had a step up switching converter that boosts the output voltage to around 4V. But I cant determine that for sure from the datasheet. They do look like pretty cool devices. They could be mounted on the PCB using standard pick-and-place.
      The price per amp seems pretty high though, and it might be tough finding an application for them with low enough current requirements. Personally I’m hoping Sparkfun starts stocking something like these:
      http://scientificsonline.com/product.asp_Q_pn_E_3081619
      They are still relativly small cells but output 10’s of milliamps (rather than microamps).

      • I am assuming they are using some kind of switcher as well to maintain the 4V.
        Also, thanks for the link! I will do some investigating to see if we can get our hands on something similar.
        Thanks!
        -Aaron

  • 4 volts from this? I bet it’s crazy low current but still, very interesting.

    • Yeah, we have yet to test that figure. The datasheet specs 50uA in full sun I believe. But still cool!


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