Generate 5V DC powersupply from 30<->300V AC source

[hpi]

Hi,

i'm developping a digital CDI-unit (engine ignition). Therefor i need to have a 5V DC power supply. The CDI is connected to the alternator (AC) of the engine and gets 30V at very low RPM till 300V at high RPM. (See 'drawing' below) One half of the ac current is used to load capacitance of 400V 1µF (for ignition purpose) the second half is used to make the 5V powersupply. The system is very sipmle and not very elegant, but it works with most types of motorcycles. It charges a capacitance of 35V 1000µF till +/- 12V and then the thyristor th1 is being ignited so the exces of energy is being sent 'away'. After this 12V capacitance, there is an 7805 for the 5V powersupply. Now some motorcycles are much more powerfull and in these cases the th1 gets enormously hot. I'm looking for a minor adjustement now to limit the power through th1 with a simple adjustement. Because the frequency varies between 5Hz-266Hz, i was thinking that the capacitance of 12V doesn't need to be charged every cycle. So at the place where the (X) is in the schematic i would like to insert a diode and a thyristor in antiparrallel. the diode is needed to be able to charge the 400V capacitance. The thyristor is needed to block the current as the 12V capacitance is still sufficiently loaded. In this case its possible that for 20 or more cycles the 12V capacitance isn't loaded and then if it's level drops below 7-8V it's being loaded again for 1 cycle.

Now the question, what what circuit can I control this thyristor (not th1, but the newly inserted one)

D1,D2,D3,D4: diodes ex.1N4007
Th1: Thysistor ex.TIC106M


Coil 30-300V AC
|OOOOOOOOOOOOOOOOOOOOOOOOOO|
| |
| |(X)
| D1 GND D2 |
|--|<-------|---------->|--|
| | Th1 |
| |------|<------|
--- | \ |
---400V 1µF | V D3
| | 35V 1000µF -
| D4 | || |
|----->|----|-----||-------|
| | || |


Thnx Tom

 

[hpi]

Ok, i'm sorry for the bad drawing. Copy paste it to notepad and it should be much better. Use courier as font.

Greetz Tom

 

[nbucska]

I can't see any complication : Reduce the current of the
5V circuit to <<10mA -- this means max. 3W at 300V and
the regulator can dissipate this with a small heatsink.

If this is for production, you can reduce it much more
with some more work...

<nbucska@pcperipherals.com>

 

[dspDad]

I love it. I ride an ST1100, and get a little surge over motorcycle projects.

Is there a reason you don't get the 5V off the 12V motorcycle supply? Is the alternator you describe the charging circuit for the bike, or is this a second alternator? If it is the bikes own alternator, then the 300 V will destroy the rectifier diodes and maybe more.

The reliability of the system over temperature seems problematic, and 3 W dissipation in a scorching hot environment might not be practical.

I might also be totally misreading the 'schematic'. I haven't seen one as complex as this in ASCII before. Nice work.

DspDad