Pozdrav ljudi,
Molim za pomoć oko parametara transformatora. Naime treba mi DC-DC invertor u sklobu izrade CDI (Capacitive Discharge Ignition) paljenja za motor. Našao sam jednu šemu koja bi mi odgovarala (pre svega u kontekstu činjenice da ostatak potrebnih komponenti već imam po kutijicama :)...).
Šema je ispod:
Izlazni napon ka ovom 1uF kondenzatoru desno treba da se kreće u granicama od 200-300 Vdc. Propratni tekst kaže sledeće:
Citat:
Features
This DC-DC converter charges a 1uF capacitor at 250 volt in aprox. 1 msec. This theorically lets the CDI spark near 1000 times per second, 60,000 rpm in a single cylinder engine (1 spark per rev), 30,000 rpm rpm in a 4 cylinder engine (1 spark each 2 revs per cylinder).
Energy performance is about 85%. For example, at 12,000 rpm in a single-cylinder engine, with a 50 mJ load is equivalent to 12000/60*0.05=10 watt, with 85% performance it is equivalent to 11.8 W (1 amp)
How it works?
This inverter uses a SMPS (switching mode power supply) oscillator to convert from 12 volt to 200-300 volt range. It uses the flyback topology instead of typical forward converter. When the MOSFET is activated the transformer begins to accumulate magnetic flux and a negative pulse is present (and not used) at the secondary coil.
When MOSFET is turned off, the magnetic energy stored inside transformer is converted to a positive pulse in the primary coil (and not used), close 50 volt, and thus is multiplied by the transformer ratio in the secondary (close 300 volt). This high voltage pulse is used to charge the CDI's capacitor through a high speed schottky diode.
Flyback topology lets a wider range for transformation better than forward converter, by changing the duty cycle. In addition it prevents the "short-circuit" effect while the capacitor is not yet loaded. As in CDI the capacitor is continuously charging and discharging, performance is very bad with a standard forward converter. While voltage inside capacitor is low, the transformer is sawn as a shorcitcuit by the mosfet, dissipating a lot of heat.
Capacitor Energy:
Energy stored in capacitor is a function of V and Capacity: E (jules)= V^2 * C * 1/2.
For example: for 1uF capacitor, charged at 250 volt, E = 0.03125 J = 31.25 mJ.
Values near 50 mJ are standard, values higher than 50 mJ are high power
Mene konkretno interesuje proračun parametara za ovaj transformator. Prvo se postavlja pitanje jezgra. Mislio sam da iskoristim feritno torusno jezgro R12.5/7.5/5 K4000 (AL vrednost je 2000 nH). U nekim komercijalnim CDI uređajima koje sam rasklapao, video sam da su korišćenja ova malena torusna jezgra a u nekim isto ovako mala EI jezgra (ceo uređaj sa ostatkom elektornike treba da stane otprilike u kutiju dimenzija 9x6x3cm).
Moje prvo pitanje je da li mogu iskoristiti gore navedeno jezgro, a drugo pitanje je koliko onda treba (i kog prečnika žice) namotaja na primaru a koliko na sekundaru. Hvala unapred...