Abstract: An electronic power supply circuit (50) that includes a rectifying circuit (14), a boost converter (16), an in-rush current reduction circuit (52), and a bulk capacitor (18). The in-rush current reduction circuit (52) includes an in-rush current limiting resistor (54) and a bypass capacitor (56) that are connected in parallel with each other. An improved version of the in-rush current reduction circuit (52) includes a bypass diode (58) connected in parallel with the in-rush current limiting resistor (54) and bypass capacitor (56) which is oriented to provide a path for current flowing out of bulk capacitor (18). One particular application of the disclosed circuit is for use in an electronic ballast for fluorescent lamps.

Abstract: A ballast for providing a dimmable fluorescent lamp (42) has a potentiometer (46) connected to AC power source (10). The potentiometer (46) is connected to a dimming circuit (44). In response to changes in the resistance of the potentiometer (46), dimming circuit (44) causes the duty cycle of a pulse width modulator (18) to change, thereby dimming the fluorescent lamp (42). A dimming disable circuit (60) disables the dimming circuit (44) when power is initially applied to the ballast (6) so that the lamp (42) will ignite.