Backyard Aquaponics
A place to discuss aquaponics

If you are trying to power a chip from a small solar panel, there is a very gradual increase in power as the sun starts to shine.

This causes problems when the chip is nearly at running voltage and nearly ready to boot.

The obvious answer is to use a battery, but would a zener diode placed back to front make it so the chip didnt see any power until the reverse voltage point kicked in?


As I understand them, a zener diode blocks current one way until they see a particular voltage, then let a specific voltage pass the wrong way.

Is this how they work?

I've watched a few videos on youtube and read the wiki page, but I still dont understand how they do what they do.

This isnt for a specific device or anything, but I read a problem on the picaxe site and it made me realize I understood even less than I thought, and that's at odds with my plan to know everything.

You can't use the zener by itself as a switch because it has a voltage drop across it equal to the reverse break down voltage. Typically zeners are used as a voltage reference to control a transistor or FET switch.

The problem is solved best by using a uP supervisor IC or the built in brown out detector in the chip if it has one. Most do.

The brown out detector is just a comparator that compares the input voltage to a set trigger level. If the input voltage drops too low, it holds the reset line.

Your thoughts are basically correct.. as the voltage rises to the Zenner - Breakdown Voltage, you will get to the point where that happens.
Immediately, current will flow, and the current will flow into the device.. but what now happens is the resistance of the device will cause a voltage drop across that device, which will lower the voltage.across the ZENNER and it will likely shut down again..
So you will end up with the same hunting issue..

There is no really simple way of covering the problem of the PV panel producing a high Voltage, B4 it is capable of providing the current needed.. unless that current is miniscule.. eg .. a computer chip, that can then analyse the power and decide is valid power is there..

The simplest way would be to use a battery AND a solar detector, so that the battery will cover the times when the PV. Is energizing or de-energising..
Ie PV voltage = operate, and assume that either the current will soon be charging the battery, or, that voltage will soon be gone, and thus when gone, the device is powered off.. All a bit clumsy

The main question I would ask is what power do you need to supply.. can you supply 24/7 from a larger panel and battery..?
..

Thanks for the answers people.

The problem was someone else's, and had to do with booting a PICAXE chip powered by a small solar panel.

I dont really need a solution, but when I was reading their post I remembered zener diodes doing some break down reverse voltage thing, and thought it might apply.

So I did my usual thing and went off to learn about them, but found I didnt really understand what I was reading and watching.

I think the reason was they all seemed to say they did exactly what I thought, and simultaneously didnt. Which it turns out they are.

So thanks for clearing it up. Instant clear answers as usual from this place after 90 minutes of wading through other stuff

I wish backyard aquaponics had been entirely responsible for my education as a kid.

Now that would be cool. Lets adopt a baby!

I just had a thought.

There is a low power sleep mode on PICAXE chips, and I wonder if the chip is sitting in sleep mode when it gets just enough power, and it never sees a command to wake it up.

Is there a simple way to build power in a capacitor until it reaches a certain level then triggers?

There must be, because my flashing bike lights stay just as bright, they just flash slower as the batteries get low.

I'm off to crack open a bike light.

[edit-I just re-red your answers and find you already answered this]

You would use a voltmeter on the negative lead to measure the voltage when the unit finally boots up and runs reliably; and choose a zener diode with a voltage rating slightly higher than that. Put the zener diode in the negative lead and no current will flow until the voltage is high enough to run the unit.