I want to power an At-tiny via induction. I have a setup which works fine turning LEDs on and off, but it will not power the Tiny. I assume, because even with a basic rectifier, the power is not consistent enough.
Attached is a schematic of what I want to build. I have a basic understanding of what I am doing, but I would like some pointers on which exact components to chose, or criteria on how to chose the components. Also, as I don't actually know what I am doing, please also point out errors in my approach.
The coil on the left is the secondary coil. (The primary coil is part of a hacked qi-complient charger. It operates at something between 120 and 200 khz. On the receiving end I measure ~5.5 Volts. The charger states that it can supply up to 1 Ampere at 5 Volts. I do not know how efficient my receiving coil is)
D1 to D4 are for rectification. These should turn from AC to a (messy) DC signal.
R1 is there in order to protect the zener diode
-ZD1 is there in order to protect my load from overvoltage
C1 is there to smooth out the signal, so that its nice and consistent when it gets to the ATtiny
Does this make sense?
Are there better ways of approaching this?
Could you recommend components to me? Or give suggestions on how to find the components I need? (digikey is allways a bit overtaxing to me. When I search for diodes there are soooo many options, half of which I do not understand.)
There should be a smoothing capacitor across the output of the bridge rectifier, before R1.
I don't know exactly how they do this in a Qi compliant charger, but in my experience, at least one side of the circuit must be a tuned LC circuit. I've had better luck using tuned receivers.
How far apart are the coils?
Most inductive charging systems need very closely coupled coils spaced only a few mm apart.
Hard to know what needs to be changed without more information about the primary coil circuitry.
I am not really worried about the coils, or about how they sync/line up etc. I also am aware that I need to add capacitors to improve resonate coupling. Right now, I want to build the circuit I drew a sketch of, but I am unsure which specific components to get. Somehow diodes just confuse me.
I was hoping somebody could tell me what to look out for in a diode, for the use I am intending.
For the diodes, I suggest a small signal Schottky diode such as BAT43. For better performance over a wide range of conditions, have the diodes feed a smoothing capacitor and then a micropower LDO regulator such as MCP1702 instead of the zener diode.
polymorph:
There should be a smoothing capacitor across the output of the bridge rectifier, before R1.
I don't know exactly how they do this in a Qi compliant charger, but in my experience, at least one side of the circuit must be a tuned LC circuit. I've had better luck using tuned receivers.
With closely coupled LC circuits the tuning will depend on both - I would have thought
the transmitter should be a high-Q tuned circuit and the reciever pretty much acts as the
losses in the system, so it should look like a lossy coil, not a tuned circuit. However the
amount of coupling is crucial, good coupling and you basically have a transformer, weak
coupling and you have a radio TX / RX where a resonant receiver is important.
Look at the Qi system it appears the transmitter is resonant, but is operated slightly
off resonance so that the receiver can easily communicate back by modulating the
receiver Q value.
The number of turns in the receiver coil is probably mainly to do with the desired voltage,
rather than setting any resonance. The transmitter modulates its output power by moving
further from resonance.
Resonant circuits are some fun stuff. I did some classes at OlyMEGA (local maker club) where I had a few turns untuned connected to a signal generator, and a few turns untuned connected to a couple of antiparallel red LEDs. Even close coupling would not light the LEDs, but if I inserted a tuned LC circuit near them, the LEDs would light.
