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:
- inductor
- switcher
- diode
- output capacitor
There is a concern with the inductor:
- the inductor magnetic core used in one B direction (as in the flyback design) has (?) worse efficiency
- than a transformer where magnetic core is used with alternating B direction (as in transformer design).
Inductor - (note: not transformer)
For experiments we can use 4 of these in parallel:
- 47 uHy 1.5A 0.14R 10% RAD * (BOU) RLB0914-470K 9.5
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.
- BY399 (3A continuous, 600V) dropped (thruhole not justified)
- SMB footprint fast ES2J that we use all over the place is perfect
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:
- 2uF 450V 10% . MOTOR MP60020061 (DNA) 25x52mm M (1.4 Euro)
0.25 A * 16 usec = 4uC
4uC / 2uF = 2V (ripple)
Output arrangement
There are 2 possible types:
- solution1: the coil+ can be connected to a capacitor charged to 400V
- and coil- switched just like it is done in an inductive app (like v3.x)
- solution2: coil- connected to GND
- cap+ charged to 400V through an inductor, than switched to GND
- coil+ powered from cap-. cap- tends to 0V when inactive, but when cap+ jumps from 400V downto 0V, cap- is forced to jump from 0V to -400V therefore activating the coil (releasing spark immediately on secondary side)
- Both has similar driver requirements: IGBT sounds better, but thyristor can theoretically work if sized well
- The number of required caps is just 1 (significant advantage) for solution1 (and 1 / channel for the solution2)
- voltage on coil is hot (referenced from GND) or solution1 even when inactive
Another supply typology?
This might be better than above flyback, mainly efficiency.
I and a friend are making some testings with single-transistor-forward-converter, we think this is the equilibrium.
The transformer is a EE30 (30mm width), frecuency is about 300Khz for 100W.
Size is shown in picture: cdi2.jpg
There are also horizontal transformer, it is better for ecu shape.
Transistor is the same than injector (20N06) but maximum current exceed 20A and we have to select another one.
The proposed shematic are this (very provisional)
Nice job, thanx. I think Keith (sly_) experimented with something similar but in ltspice only.