CdiSupply (2005-06-11 12:30:51)

For inspiration i link to old type BOSCH CDI ignition box schematic, and layout can be studied here

http://forums.pelicanparts.com/showthread.php?s=&threadid=203100&highlight=6pin+cdi

link by MembersPage/SteenAndersen

CDI-schematic

http://www.highlandsun.com/hyc/ignition/

Some info..

http://www.beyond-designs.com/pspice_CD.htm


CDI requires an appr. 400V DC supply

We want to be safe, so 100W power should be targetted (0.25A output current).

Input is 14V as usual.

I was thinking about CDI supplies. I built a transformer based supply earlier (somewhat lower wattage).

The best I can come up with is a simple flyback design. This has the lower part-count, beautiful simplicity (including testing!) If power was >300W a transformer based might become more attractive.

We need to use many thruhole parts in any case.

Flyback design consist of only 4 major parts:

There is a concern with the inductor:


Inductor - (note: not transformer)

For experiments we can use 4 of these in parallel:

The same barrel type/size as the 1.5uH 5.4 A we use on v3.x.

Finally we'll wind our own toroid or whatever type.

(12V / 12uH) < (16A / 16usec)

16A peak is a bit high (for the IGBT too, and definitely for the diode). 16A peak means about 16A / 2 * 12V=100W.


IGBT

similar to what we have now, but to make 400V possible, clamping at 370V is not desired.

FETdriver is needed to drive the gate at 64 usec (15625 Hz).


Diode

To get 10A diode from 5 pieces of 2 A diodes is slightly more complex than simple parallel connection because of the -2mV/K temperature coefficient, the one with lowest voltage will overheat itself. Series resistors (for each diode, maybe trace is enough) can fix that.

Maybe 6..7 SMB in parallel and 0.022 Ohm in series with each.


Caps

Electrolitic cap is not the best idea at 16 usec period.

It might even explode. Some testing is needed in any case. Other cap that might work:

0.25 A * 16 usec = 4uC

4uC / 2uF = 2V (ripple)


Output arrangement

There are 2 possible types:


Another supply typology

Push-pull type

Push-pull use better the transformer, it can get more power with smaller transformer than forward, it needs two transistors.

There are some questions about CDI:

Are fired with Thyristors or IGBT? If it use Thyristor the supply must be shutdown when thyristor is actived until capacitor was discharged.

if IGBT are used, it is not necessary to shutdown supply but IGBT have to be fired with a precise pulse wide. Is it possible to configure ignition pulse wide in CDI mode?

board_small.gifpush-pull_small.giftransformers_s.jpgassembly_s.jpg
board.gifpush-pull.giftransformers.jpgassembly.jpg

It seems to work, At the moment i have meassured 100w at 350v, but it releases a lot of heat and the performance is not much high, I think it could be solved with a optimum design of the transformer, testing several transformers are hard-working.

current transformer is about 30 x 30 mm size, but i think it could fit a smaller one, with more frequency. It could be really small!!!