Clean DC from wildly varying AC
Clean DC from wildly varying AC
(OP)
Hello all,
I have a pet project that is giving me a headache.
I am trying to power a microcontroller circuit from a magneto. The magneto is an AC source which varies in frequency from about 2 to 40 kHz. Waveform is very roughly sinusoidal, with peak voltage varying from about 8 to over 100 volts. Voltage peak increases with frequency.
The microcontroller and associated circuitry (mostly LEDs) will require max 2 A at 5 V.
I have been wrestling with this for a while. So far the best I have come up with is a 1:1 transformer to tap some power without affecting the rest of the system. Then a diode bridge followed by a zener diode and an emitter follower as an active clamp. After this caps and a linear regulator. I am worried the large variation in the AC's peak voltage will cause problems. I would also like to minimize wasted power as much as is possible.
Thanks for your help.
I have a pet project that is giving me a headache.
I am trying to power a microcontroller circuit from a magneto. The magneto is an AC source which varies in frequency from about 2 to 40 kHz. Waveform is very roughly sinusoidal, with peak voltage varying from about 8 to over 100 volts. Voltage peak increases with frequency.
The microcontroller and associated circuitry (mostly LEDs) will require max 2 A at 5 V.
I have been wrestling with this for a while. So far the best I have come up with is a 1:1 transformer to tap some power without affecting the rest of the system. Then a diode bridge followed by a zener diode and an emitter follower as an active clamp. After this caps and a linear regulator. I am worried the large variation in the AC's peak voltage will cause problems. I would also like to minimize wasted power as much as is possible.
Thanks for your help.





RE: Clean DC from wildly varying AC
You must use diodes for the bridge that are fast enough for 40kHz,(not a big problem).
Charge a cap with an appropriate voltage and temperature rating that exceeds the magneto's output ability.
Select and use a buck switching controller to draw from the varying voltage stored on the cap to create whatever voltage you seek.
If you are actually using this result only to run LEDs then you should seek to make the buck regulator a current regulator instead of a voltage regulator.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Clean DC from wildly varying AC
I'd use a switching voltage regulator for voltage control. Use capacitors and a choke on the output to clean up the current spikes to reduce rf interfernce. I would probably run it with a choke at the output followed by a few capacitors. You can also use a diode to clean this up even more.
I would stay away from the linear regulator just due to heating reasons. If you have 100 Volts peak, and are bringing that down to 5VDC at 2 Amps, that is going to be a tremendous amount of heat for the linear regulator to dissipate. A switching regulator uses short pulses and therefore will be significantly more efficient.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Clean DC from wildly varying AC
RE: Clean DC from wildly varying AC
An SMPS with an exceptionally broad input voltage range is probably the best solution. But still doubting if you can have your 2 amps at 5 V when running at low speed.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Clean DC from wildly varying AC
RE: Clean DC from wildly varying AC
I was hoping using a SMPS with 4-60 volt input would allow the zener, as I would only have to clip above 60 V. Is there a better method?
The low end is a problem. I haven't checked output of the exact magneto, but a very similar one I looked at a while ago had this output. I will be able to check out the exact output soon, hopefully it will be a bit better.
OperaHouse, the LEDs are not in series as I need to individually control them.
RE: Clean DC from wildly varying AC
RE: Clean DC from wildly varying AC
I'm not talking a linear! You need to draw 2A x 5V = 10W from the magneto.. That means at 80V only 125mA.
If you don't want to deal with the 100V then just add in a voltage controlled switch between the rectifiers and the cap that disconnects the cap whenever the cap voltage exceeds 50V. You're following the cap with a switching regulator it will use whatever the cap has on it and does not care that the cap voltage moves around.
If you are trying to run this thing down in the ditch where you shouldn't be, getting full power from it at 8 volts, you should check to see that the then required 2A is not going to be too much for the magneto's windings. If this is still OK then just select a buck/boost switching regulator. They can boost the voltage as well as buck the voltage. I'd still review the logic for that.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Clean DC from wildly varying AC
Here's what I can come up with: two separate power sources.
Use a single diode (halfwave rectifier) to get your DC. Use a large capacitor as a filter to smooth the ripple. Now you need some type of selector switch, I'd use a DPDT two pole relay. A mechanical type might work fine if you can handle a short power dip in the order of a 200mS. You'll need a voltage sensor of some sort to switch the relay when output voltage exceeds 50V.
The relay will then drive two separate voltage regulators. One with be the 60V max input 5V switching regulator with a choke and added filter capacitor. The second will be a two stage regulator. The first stage would be some buck regulator that can get your voltage down below your 60V threshold, and from there you can use the 5V switching regulator as in the first output.
I think that should do it for you. I can't think of any other way to overcome the issue, but perhaps someone else has an idea.
Use a switching regulator to get your 5V.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Clean DC from wildly varying AC
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Clean DC from wildly varying AC
Until then, Happy New Year everyone.
RE: Clean DC from wildly varying AC
Dan - Owner

http://www.Hi-TecDesigns.com