Linear Technology Corporation

Analog Devices International Unlimited Company

Linear Technology Holding LLC

Keith Szolusha

Min Hao Chen

Xugang Ke

Joshua William Caldwell

Shuilin Tian

Eric Stephen Young

Bryan Avery Legates

Brooks R Leman

Xin Qi

Yonghwan Cho

Yaojie Xu

Nancy Tarng

Min Chen

The Kappa converter circuit, as introduced herein, can be configured for step-down (buck), step-up (boost), or buck-boost operation. The Kappa converter circuit exhibits lower electromagnetic interference (EMI) relative to other buck, boost, or buck-boost topologies, such as without additional input or output filter circuits. The Kappa converter circuit can have high power handling capability and less DCR loss, for example due to a distribution of current signals through respective inductors. The Kappa converter circuit includes isolating inductors at its input and ground reference nodes to help reduce signal bounce or signal pulsations at supply and ground reference busses, thereby further reducing EMI noise due to switching in the circuit. When the Kappa converter is configured for step-up operation, the converter exhibits no right-half-plane (RHP) zero.

Kappa switching DC-DC converter with continuous input and output currents

A switching power converter circuit comprises an inductor arranged to receive input energy from an input circuit node; a switch circuit coupled to the inductor; a load current sensing circuit element coupled to a regulated circuit node and an output circuit node; a compensation circuit coupled to a compensation circuit node; a control circuit coupled to the compensation circuit node and the switch circuit, the control circuit configured to modulate activation of the switch circuit to regulate a voltage at the regulated circuit node; and a feedforward circuit coupled to the load current sensing circuit element and the compensation circuit, and configured to adjust modulation of the switch circuit according to sensed load current.

Load current feedforward schemes for current-mode controlled power converters

A technique to eliminate perceptible flickering by LEDs being dimmed by PWM pulses is disclosed. A controllable oscillator controls a switching frequency of a converter for supplying a regulated current or regulated voltage. The converter controls a first switch at a switching frequency. A varying second signal level is generated by a spread spectrum control (SSC) circuit for controlling the oscillator to vary the switching frequency during operation. A PWM dimming circuit generates a string of PWM pulses that control a switch in series with the LEDs. The SSC circuit is synchronized with the PWM pulses to generate the same second signal level at a start of each PWM pulse, such that the switching frequency of the converter is forced to be substantially the same at the start of each PWM pulse while the pulse widths are constant. The repeating driving current waveform eliminates perceptible flicker by the LEDs.

PWM control for LEDs with reduced flicker when using spread spectrum switching frequencies

A supply circuit comprises a regulated positive supply circuit and an unregulated negative supply circuit. The regulated positive supply circuit includes an inductor arranged to receive input energy from an input circuit node, a switch circuit coupled to the inductor at a switch circuit node, and a control circuit coupled to the switch circuit. The control circuit is configured to control activation of the switch circuit to regulate a voltage at a regulated circuit node and generate a positive output voltage at a positive output circuit node. The unregulated negative supply circuit is operatively coupled to the switch circuit node and is configured to generate a negative supply voltage at a negative output circuit node.

Negative charge pump doubling output voltage range for step-up LED driver

A converter has a boost portion and a buck portion. The boost portion supplies a boosted voltage and includes a first inductor having a first end coupled to the input terminal, a first switch coupled to a second end of the first inductor to charge the first inductor when the first switch is in its on-state, and a first capacitor for being charged to the boosted voltage. The buck portion supplies an output voltage to a load that is less than the boosted voltage and includes a second inductor in series with the load, and a second switch in series with the second inductor and the load to charge the second inductor during an on-state of the second switch. A single controller IC receives feedback signals and controls the switches to have the same duty cycle to achieve a regulated load current or voltage with low EMI.

Boost then floating buck mode converter for LED driver using common switch control signal

A converter generates an output voltage differential across a floating load, such as a string of LEDs. The converter receives an input voltage Vin from a power supply, and the floating output voltage differential may be greater than or less than Vin. The converter uses a first switch and first inductor in a boost mode type configuration, and uses a second switch and second inductor in a buck mode type configuration. The inductors have a common node. The first inductor has another end coupled to ground, and the other end of the second inductor is coupled to the load. Both inductors charge and discharge together depending on the conductivities of the switches. One end of the load will be approximately zero volts, while the other end will be at a negative voltage VEE. The two inductors smooth input current/voltage ripple and output current/voltage ripple, resulting in low EMI.

Floating output voltage boost-buck regulator using a buck controller with low input and low output ripple

An LED driver uses a positive-to-floating boost converter topology to generate a negative voltage &#x2212;Vee relative to ground. The converter receives an input voltage. Vin from a power supply. One end of an output inductor is coupled to ground, and the other end of the inductor is coupled between a highside switch and a low side switch. The bottom terminal of the lowside switch generates &#x2212;Vee. The anode end of an LED string is coupled to Vin and the cathode end is coupled to &#x2212;Vee. The converter detects the LED current and regulates the switching duty cycle so that the LED current is equal to a target current. This is more efficient than coupling the anode end of an LED string to ground and the cathode end to &#x2212;Vee. A conventional buck controller IC may be used.

Floating output voltage boost regulator driving LEDs using a buck controller

In a method for controlling a current regulator for dimming an LED load, a dimming signal has a duty cycle that controls the LED ON-time and LED OFF time at a fixed frequency. The regulator is controlled by the dimming signal to only supply current to the LED load during the LED ON-time. The regulator includes an inductor. The inductor current at the end of an ON-time is detected and its value is stored. During the OFF-time, the inductor is pre-charged to the current level matching the stored value, while the regulator's feedback loop is frozen during the OFF-time to not change its feedback control signal. Upon the next ON-time, the regulator begins supplying current to the LED load with the pre-charged inductor current, so there is no initial decrease in the delivered LED current. Therefore, the current pulse magnitudes are constant even with very low duty cycles.

Pre-charging inductor in switching converter to achieve high PWM dimming ratio in LED drivers

In a method for controlling a current regulator for dimming an LED load, an adjustable delay circuit generates a delayed second dimming signal from an original first dimming signal. The second dimming signal has a duty cycle that controls the LED ON-time and LED OFF time at a fixed frequency. An ON-time pulse of the first dimming signal starts a pre-charging of the regulator's inductor to approximately the inductor current previously detected at the end of the previous ON-time of the LEDs. The pre-charging ends at the leading edge of the delayed ON-time pulse of the second dimming signal. The second dimming signal controls the regulator to only supply current to the LED load during the LED ON-time. The delay time is adjusted by a feedback loop. Therefore, the current pulse magnitudes applied to the LED load are constant at every duty cycle even with very low duty cycles.

Pre-charging inductor in switching converter while delaying PWM dimming signal to achieve high PWM dimming ratio in LED drivers

A switch mode converter converts an input DC voltage applied at one level at the converter input to an output DC voltage at a second level at the converter output. A switch is arranged to switch the input DC voltage on and off during each cycle of a plurality of cycles. An energy storage unit temporarily stores energy from the input source voltage when the switch is on, and releases energy when the switch is off during each cycle. Input energy stored is equal to the energy released with each cycle and achieves equilibrium when the converter is operating into normal loads. A reset mechanism provides additional reset voltage during each cycle to achieve equilibrium when the converter is operating in a fault condition.

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Saratoga, CA, United States of America

Keith Szolusha