Constant current and voltage controller carrying out pin multiplexing and a three-pin package

Abstract

A flyback converter includes a controller integrated circuit (IC) housed in an IC package with only three terminals. An inexpensive TO-92 transistor package can be used. A switch terminal is coupled to an inductor switch that is turned on by a switch control signal having a frequency and a pulse width. The inductor switch controls the current that flows through a primary inductor of the flyback converter. The controller IC adjusts the frequency in a constant current mode such that output current remains constant and adjusts the pulse width in a constant voltage mode such that output voltage remains constant. A power terminal receives a feedback signal that is derived from a voltage across an auxiliary inductor of the flyback converter. The feedback signal provides power to the controller IC and is also used to generate the switch control signal. The controller IC is grounded through a ground terminal.

Description

technical field

[0001] The invention relates to the field of power conversion, in particular to a switching mode power supply circuit which only uses three pins to regulate output current and output voltage. Background technique

[0002] Various integrated circuit chips are currently used to control flyback converters that provide constant current and constant voltage. figure 1 (Prior Art) An exemplary prior art constant output current flyback converter 10 is illustrated, which is controlled on the primary side of a transformer 11 . Although the flyback converter 10 saves the cost of optocouplers typically used in secondary-side controlled converters, the flyback converter 10 requires the use of a relatively expensive integrated circuit package. The flyback converter 10 includes an integrated circuit package with six pins for mating with a conventional peak current mode pulse width modulation (PWM) controller integrated circuit (IC) 12 . Typically, IC packages with more pi...

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