Ok, first off, let's get one thing strait . . .
You guys rock!
This was exactly what I was looking for, and a great explanation for the aspiring novice.
I've been doing my research so that I can make a reasonably intelligent reply to your most informative posts.
@ steve
Thanks for the link, it was most informative.
4) get another zener with the same relationship to the output voltage you require. e.g. if the zener is 4.3 volts for a 5.0 volt output, then for 3.7 volts, you need a 3v zener.
5) fit the new zener and measure the output voltage.
Just to make sure I'm interpreting this correctly steve, you mean that once I verify the relationship between the zener voltage and final output voltage, I may then expect that my
final output voltage will vary in proportion to the difference between the old & new zener diodes?
(e.g. replacing a 4.3v with a 3.9v should result in the output dropping from 5.0v to 4.3v ??)
[note, this is taking into consideration your comments about zener tolerances:]
Don't be surprised if it's not exactly what you expect (but it should be close)
zeners are quite "loose" regulators. They have an absolute tolerance of 5 or 10%, a temperature coefficient, and a knee plus a slope on their voltage regulation.
Odd voltage readings with USB cables
~5.12 directly from the charger
5.31 from a 4' USB-A extension
5.37 from the extension + a 4' USB-B cable
5.38 from the USB-B cable only
Might this be because this simple power supply is not "regulated" (with exception to the zener) and I will only get a steady voltage rating when it is connected to the load?
- if so, then
should I make an effort to test the voltage under load? or
-
will the fluctuations scale proportionally?
(a side note, plunging in cables and testing of the charger resulted in HAVOC on my AM radio [1020 Khz] )
Battery or Capacitor ??
The camera not working when charging is most likely due to some other reasons than voltage.
Removal of the protection/sensor circuit may lead to some objections by the camera
@ Resqueline
this detail may be more helpful to me than you know.
In 'phase 2' of this project I was planning on replacing the battery with a capacitor capable of powering a 150ma load for ~30 sec.
It now occurs to me that I might instead build a charging circuit, and allow the native battery to preform this function.
(although I would think that there would need to be overcharge protection considerations, possibly a factor for the capacitor idea)
Project's main objective
This project centers around a motion triggered camera I will be using for surveillance outside that is connected to a light. When the light turns on, I want it to power on my camera. (the camera starts and stops recording based on motion)
The problem, however is that if the power fails before the camera saves the video, it will not be saved to the memory.
Thus I will require a buffer long enough to allow the camera to time out and save the video before powering down.
[advantages I perceive for the capacitor over the battery are frequent and brief usages, resulting in what would be a tough cycle for the Lithium Polymer battery.]
I am content at this point to focus on the constant power aspect of this project. (first stand, then fly ;-)
It has been educational as well thanks to your pithy replies.
I stumbled on to another candidate device in my research, if you can give your opinion on it's feasibility:
LED drivers . . . an alternative?
This unit promises 3.5~3.8v @ 2amps.
http://www.dinodirect.com/5W-3-5V-3-8V-2A-Constant-Current-LED-Driver-110V-240V-AC.html
Since I'm looking for the smallest package possible, this solution seems very desirable.
Since this circuit was not designed for the purpose I want it for, do
you think this is a good idea?
Can you point out any drawbacks?
Next research item, optocouplers
Although I am eager to complete this project, I also intend it to be a learning process.
So in an effort to better understand this charging circuit, I will next be doing the necessary research to fully understand how the remaining components affect the output voltage as summarized by Resqueline:
If you add to this the 1.2V forward voltage drop of the IR-diode in the optocoupler you get 5.5V out which is a common value.
I'm off to do more optocoupler research to determine why it adds voltage instead of lowering it. [I take the 817B to be between the usual CTR of 10-50%]