Dual Output, 4w Dc-dc Converter

Circuit Description This Design Note illustrates a dual output, 4 watt, isolated dc-to-dc converter originally intended for fluorescent lighting applications. The converter is designed around ON Semiconductor’s NCP1031 monolithic dc-to-dc switcher IC. The chip contains all of the control functions for a low power converter including an integrated 200 volt internal MOSFET This particular design, with the appropriate circuit and component modifications CAN also be made to operate with nominal dc input voltages anywhere from 12 volts to 70 Vdc and with other output voltages depending on the particular application. The dc input includes an EMI ripple Filter comprised of L1 and C1 followed by a flyback dc-to-dc converter composed of transformer T1, and U1, the NCP1031 controller MOSFET Once started via the input voltage on pin 8, the controller operates from an auxiliary Vcc voltage generated by the lower primary side bias winding of T1. This voltage is rectified by D2 and filtered by Vcc capacitor C5. The NCP1031 includes input over-voltage and under- voltage shutdown sensing via pins 5 and 6 respectively. To minimized voltage spikes created by T1’s leakage inductance, the snubber network of D1, C3 and R1 is included. Output overload protection is also provided within the NCP1031 by sensing the peak MOSFET current. Additional collateral from ON Semiconductor y NCP1031 Current Mode Controller Fixed Frequency Operation y MMSD4148 1N4148 : 100 V Switching Diode y TL431A Programmable Precision Reference y MBR20100 1A, 40 V Schottky Rectifier
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Dual Output, 4 Watt DC-DC Converter using ON Semi NCP1031
Dual Output, 4 Watt DC-DC Converter using ON Semi NCP1031



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