AT1454 Datasheet, PDF (14/18 Pages) Aimtron Technology – Photoflash Capacitor Charger for DSC

AT1454/AT1454A/AT1454B
Preliminary Product Information
Photoflash Capacitor Charger for DSC
Leakage Inductance and Parasitic Capacitance
The leakage inductance on the primary of the transformer results in the first spike
voltage when NMOS turns off. The spike voltage is proportional to the leakage
inductance. The spike voltage must not exceed the dynamic rating of the NMOS drain
to source voltage. It is important not to minimize the leakage inductance to a very
low level. Although this would result in a very low leakage spike, the parasitic
capacitance of the transformer will be high between windings. This will result in the
initial spike of current in the primary becoming excessively high while the NMOS
turns on. Therefore, trade off is necessary between leakage inductance and parasitic
capacitance.
Spike Voltage @Switching，Time(1us/Div)
Swing Current @Switching，Time(1us/Div)
V_LX(5V/Div) , I_PRI(1A/Div)
V_LX(10V/Div) , I_PRI(1A/Div)
Spike Voltage
CH1
Swing Current
CH2
CH1:V_LX; CH2:Input Current
Transformer Secondary Capacitance
The total capacitance on the secondary of the transformer will severely affect the
efficiency of the circuit. Any secondary capacitance is multiplied by N² when
reflected to the primary. Since this capacitance forms a resonant circuit with the
primary leakage inductance of the transformer. As such, both the primary leakage
inductance and secondary side capacitance should be minimized.
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: [phone] Fax: [phone]
WWW: http://www.aimtron.com.tw
3/24/2006 REV:1.2
Email: [e-mail]
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