US 5,710,697 A · Power supply controller having frequency foldback and volt-second duty cycle clamp features

Abstract

A power supply controller implementing frequency foldback and volt-second duty cycle clamp features. An oscillator timing capacitor is charged with a fixed current and is discharged with a fixed current when the output voltage is above a predetermined level and with a decreasing current when the output voltage falls below the predetermined level, so as to decrease the power supply operating frequency during short circuit or overload fault conditions. A volt-second duty cycle clamp circuit limits the duty cycle to a maximum value which is independent of the tolerance of a capacitor which sets the maximum duty cycle as a function of the power supply input voltage.

Claims21

Dependent claims

A power supply controller for controlling the duty cycle of a power supply switch as a function of an oscillator ramp signal generated across a timing capacitor in order to provide a regulated output voltage, said power supply controller comprising:

a first current source for charging the timing capacitor with a first fixed current;
and
a second current source for discharging the timing capacitor with a second fixed current when the regulated output voltage is greater than a predetermined level and for discharging the timing capacitor with a variable current when the regulated output voltage is less than said predetermined level.

A power supply comprising:

a power switch operable at a variable duty cycle to convert an input voltage to a regulated output voltage;
a timing capacitor across which an oscillator ramp signal is generated, wherein said variable duty cycle is a function of said oscillator ramp signal;
and
a power supply controller responsive to said oscillator ramp signal for providing a drive signal to said power switch to control said variable duty cycle, said power supply controller comprising:
a first current source for charging said timing capacitor with a fixed current;
and
a second current source for discharging said timing capacitor with a fixed current when said regulated output voltage is greater than a predetermined level and for discharging said timing capacitor with a variable current when said regulated output voltage is less than said predetermined level.

4 more elements

A power supply controller for controlling the duty cycle of a power supply switch which is operable to convert an input voltage to a regulated output voltage, said power supply controller comprising:

a volt-second duty cycle clamp circuit for limiting the duty cycle of the power supply switch to a maximum duty cycle set as a function of the voltage across a capacitor charged by a charging current inversely proportional to the input voltage, wherein said capacitor has a tolerance associated therewith and said maximum duty cycle is independent of said tolerance of said capacitor.

A power supply comprising:

a power switch operating at a duty cycle to convert an input voltage to a regulated output voltage;
and
a volt-second duty cycle clamp circuit for limiting said duty cycle of said power switch to a maximum duty cycle set as a function of the voltage across a capacitor charged by a charging current inversely proportional to said input voltage, wherein said capacitor has a tolerance associated therewith and said maximum duty cycle is independent of said tolerance of said capacitor.

Dependencies are inferred from the claim text.

Power supply controller having frequency foldback and volt-second duty cycle clamp features

Life of this patent

Power supply controller having frequency foldback and volt-second duty cycle clamp features

Life of this patent

Abstract

Claims21