Semtech Corporation

Silanna Asia Pte Ltd

William E Rader, Iii

John Kenneth Fogg

Robert Eric Fesler

Yashovardhan R Potlapalli

David Paul Keesor

Ryan Foran

Joseph Michael Andruzzi

A transistor is switched on and off with an on-time that is held constant and an off-time that is varied. When the off-time is detected to be less than a threshold value that is greater than a minimum off-time limit, the on-time is extended. Then the power transistor is switched on and off with the extended on-time that is held constant and the off-time that varies.

Extending on-time for power converter control

A power transistor is switched on and off with an on-time that is held constant and an off-time that is varied. When the off-time is detected to be less than a threshold value that is greater than a minimum off-time limit, the on-time is extended. Then the power transistor is switched on and off with the extended on-time that is held constant and the off-time that varies.

A plurality of LEDs is driven in parallel, in at least two modes. In a first mode, the LEDs are driven with a first voltage. In subsequent modes, the LEDs are driven with successively higher voltages. The forward voltage drop for each LED is monitored, and the driver switches from the first mode to successive modes based on the largest of the LED forward voltage drops. The current through each LED is controlled by directing a reference current through a first digitally controlled variable resistance circuit, and directing the LED current through a second digitally controlled variable resistance circuit having substantially a known ratio to the first variable resistance circuit and connected in series with the LED. A digital count is altered based on a comparison of the first and second currents, and the first and second variable resistance circuits are simultaneously altered based on the digital count.

Method and apparatus for driving LED's

Method and apparatus for driving LEDs

A charge pump power supply includes two or more modes of operation. An input protection circuit is connected between an input of the power supply and a voltage source. The input protection circuit regulates the voltage at the input of the power supply, limits current at the input when switching from a weaker mode to a stronger mode, and prevents current reversal when switching from a stronger mode to a weaker mode. In some modes, the power supply continuously provides current to the load, obviating the need for an output capacitor.

Charge pump with current limiting circuit

An apparatus and method for virtual current sensing in a DC-DC switched mode power supply. In a fixed frequency implementation, when a switching phase begins, the phase node goes high when the high-side switching transistor is turned on. At this point, a first programmable current source begins charging a current sensing capacitor and the voltage across the capacitor simulates the rising slope of the voltage across a conventional current sensing resistor. Simultaneously, a ramp capacitor beginning at a reference voltage is charged by a second programmable current source. When the sum of the voltages across the two capacitors exceeds an error voltage, the phase node goes low when the drive signal to the transistor is turned off. At this point, a third programmable current source begins discharging the current sensing capacitor and the voltage across the capacitor simulates the falling slope of the current across the conventional resistor.

Method and apparatus for virtual current sensing in DC-DC switched mode power supplies

A step-down switched-mode power supply circuit includes a transformer having at least one primary winding and at least one secondary winding, a current sensing device for sensing a current through a primary winding of the transformer, a first switch and a second switch, a first comparator for determining if the current through the current sensing device exceeds a threshold, a voltage regulator coupled to the secondary winding to produce a regulated voltage, a second comparator for determining if the regulated voltage has drooped below an acceptable level, a counter coupled to the second comparator for generating a signal having a fixed number of switch cycles, and control circuitry for generating signals controlling the first switch and the second switch and responsive to the first comparator to enter a power saving mode disabling the signals, and to the second comparator to temporarily exit the power saving mode for a fixed number of cycles when the regulated voltage has drooped below an acceptable level.

Growing community of inventors

Carrboro, NC, United States of America

William E Rader, Iii