Rohm Co., Ltd.

Kenichi Fukumoto

Hiroyuki Fujita

Hiroki Toda

Yosuke Aoyagi

Junichi Hagino

Yousuke Aoyagi

Goang-Woo Nam

Junichi Itai

Yoshikazu Sasaki

Nobuaki Matsui

Ryosuke Kanemitsu

Koji Katsura

Yoshinori Imanaka

Masao Yonemaru

Kouji Miyamoto

Seiji Nakashima

An LED drive circuit drives an LED module. The LED module has a light-emitting diode, and an identification unit having characteristic information relating to light-emitting characteristics of the light-emitting diode. The LED drive circuit includes a detection unit and a drive circuit. The detection unit is provided for detecting characteristic information, and generates a detection signal that corresponds to the characteristic information. The drive circuit generates drive current by a drive signal supplied according to the characteristic information based on the detection signal, and supplies the drive current to drive the light-emitting diode.

LED drive circuit, LED drive device, and LED drive system

A control circuit of a driving circuit of a backlight LED is provided. The driving circuit includes a DC/DC converter that supplies a driving current to the backlight LED. The control circuit includes a pulse signal generating circuit configured to switch between a quasi-resonant mode and a continuous current mode to generate a pulse signal based on a selected mode and a driver configured to drive the DC/DC converter based on the pulse signal.

Driving circuit of LED for liquid crystal backlight, control circuit thereof, and electronic device

An LED driving circuit drives a display backlight LED string including multiple LEDs connected in series. A power supply supplies a driving voltage from an output terminal thereof to a first end of the LED string. A detection resistor is arranged between a second end of the LED string and a fixed voltage terminal. The LED driving circuit receives a pulse modulation signal having a duty ratio that corresponds to the luminance. In the on period, in which the PDIM signal is the first level, the LED driving circuit controls the power supply such that the voltage drop across the detection resistor approaches a predetermined target value. In the off period, in which the PDIM signal is the second level, the LED driving circuit stops the control operation for the power supply.

Circuit and method for driving LED string for backlight, and backlight and display device using the circuit

A charge-discharge circuit charges or discharges a capacitor having a fixed electric potential at one end. A first comparator compares an output voltage of the capacitor with a first threshold voltage and outputs a first comparison signal in accordance with a comparison result. An edge detecting circuit detects an edge of a synchronization signal input from the outside and having a frequency of about &#xbd; of a triangular-wave signal generated by the triangular-wave generating circuit, and outputs an edge detection signal that will be at a predetermined level for each of the detected edges. A charge-discharge controller receives the first comparison signal that is output from the first comparator and the edge detection signal that is output from the edge detecting circuit, and switches between a charge state and a discharge state of the charge-discharge circuit in accordance with a level transition of these signals. A voltage of the capacitor is output as a triangular-wave signal.

Triangular-wave generating circuit synchronized with an external circuit

A switching circuit includes multiple transistors connected to the primary winding of a transformer, and alternately applies an input voltage and a ground voltage to the primary winding according to the ON/OFF operations of the transistors. Multiple ballast capacitors are respectively provided to multiple fluorescent lamps. One terminal of each ballast capacitor is connected to the secondary winding so as to form a common terminal. The other terminal thereof is connected to the fluorescent lamp. A first capacitor and a second capacitor are arranged in this order in series between an connection node that connects the fluorescent lamp to be monitored and the corresponding ballast capacitor and the ground terminal. An abnormal state judging unit compares the voltage at the connection node that connects the first capacitor and the second capacitor with a predetermined threshold voltage.

Inverter apparatus

A soft start circuit generates a soft start voltage which changes over time when light emission of an EEFL is started. A pulse modulator receives a feedback voltage that corresponds to the output voltage of an inverter and the soft start voltage, and adjusts the duty ratio of a pulse signal PWM such that these two voltages match one another using a feedback operation. A striking control circuit monitors an error signal which is asserted when an abnormal state occurs. In a case in which the error signal has been asserted at a detection timing after the soft start voltage has reached a target voltage, the striking control circuit resets and restarts the soft start circuit. A driver controls the switching of the voltage at the primary coil of a transformer according to the pulse signal received from the pulse modulator.

Inverter

In an apparatus for driving a CCFL, a first inverter outputs a first alternating current (AC) voltage to one end of the CCFL. A second inverter outputs a second AC voltage having a reversed phase to the first AC voltage to the other end of the CCFL. A first current-voltage converting circuit converts a secondary current of a first transformer in the first inverter to a voltage and outputs the voltage as a first detection voltage. A second current-voltage converting circuit converts a secondary current of a second transformer in the second inverter to a voltage and outputs the voltage as a second detection voltage. A first abnormality detection circuit determines a circuit abnormality when the potential difference between the first and second detection voltages exceeds a predetermined first threshold voltage.

Fluorescent lamp driving apparatus with abnormality detection circuit

A first comparator compares an output voltage Vout appearing at a capacitor with a maximum threshold voltage Vmax. A second comparator compares the output voltage Vout with a minimum threshold voltage Vmin. An edge detection circuit detects an edge of a synchronization signal SYNC having approximately &#xbd; of frequency of the output voltage Vout and outputs an edge detection signal SE. A charge-discharge control unit refers to the first and the second comparison signal, and sets the charge-discharge circuit to a discharging state when the output voltage Vout becomes higher than the maximum threshold voltage Vmax and sets the charge-discharge circuit to a charging state when the output voltage Vout becomes lower than the minimum threshold voltage Vmin. When the edge signal SE becomes the predetermined level, the charge-discharge control unit switches the charging state and the discharging state of the charge-discharge circuit.

Triangular-wave generating circuit, and inverter, light emitting device and liquid crystal television using the circuit

A pulse width modulator generates a PWM signal whose duty ratio is feedback-controlled so that a detection voltage according to a current across a secondary coil of a transformer is brought close to a reference voltage. A logic control unit performs a switching control of the current across the primary coil of the transformer, based on the PWM signal outputted from the pulse width modulator. A first protection circuit detects a circuit failure of an inverter and stops the switching control of the inverter when the circuit failure continues for a predetermined duration of error detection time. A second protection circuit monitors a feedback voltage corresponding to an output voltage of the inverter, and lowers the reference voltage sets the duration of error detection time short when the feedback voltage is lower than a predetermined threshold voltage.

Inverter with protection function

A soft start circuit generates a soft start voltage Vss which changes with time at a starting time of lighting an EEFL. A pulse width modulator generates a PWM signal Vpwm whose duty ratio is feedback-controlled so that a feedback voltage Vfb corresponding to an output voltage Vdrv of an inverter conforms to the soft start voltage Vss. A logical control unit performs switching control of a voltage of a primary coil of a transformer on the basis of the PWM signal Vpwm from the pulse width modulator. The soft start circuit executes at least one striking operation in which the soft start voltage Vss is raised with time, lowered when being reached to a first voltage level VH, and raised again when being lowered to a second voltage level VL lower than the first voltage level VH.

An inverter has a semiconductor switch circuit provided in the primary circuit of a transformer. The switch circuit is controlled by a PWM circuit. The switch circuit is operated on the basis of an intermittent-operation signal having an ON state and OFF state to: set an error signal to a substantially zero level during OFF periods; gradually increase the error signal upon transition from an OFF state to an ON state; and gradually decrease the error signal upon transition from an ON state to an OFF state. Each ON phase of the intermittent operation is slowly started and slowly ended through charging and discharging of a capacitor provided in a feedback circuit. This enables concomitant application of constant-current control and intermittent-operation control to the inverter, which in turn provides a broad range of power that can be supplied to a load, significantly reduces hamming of the transformer, and prevents over-current from occurring in the inverter.

DC-AC converter, controller IC therefor, and electronic apparatus utilizing such DC-AC converter

A DC power source voltage is supplied to a center tap of a primary winding, and first and second semiconductor switches alternately turned on are disposed between each of both ends of the primary winding and a common potential point, and a current flowing through a load is fed back and PWM control of each of the semiconductor switches is performed. Also, snubber circuits are respectively connected between a ground and the center tap of the primary winding, and an abnormal high voltage at the time of switching is reduced. Also, a parallel running of plural inverters is simply performed by disposing PWM comparators corresponding to the first and second semiconductor switches.

Controller IC, DC-AC conversion apparatus, and parallel running system of DC-AC conversion apparatuses

The switching timing is flexibly set in an inverter. An H-bridge circuit is controlled based on a triangular wave signal and an error voltage. To control the circuit, a first high-side transistor and a second low-side transistor are turned on in a first period until the triangular wave signal reaches the error voltage. The first high-side transistor is turned on in a second period until the triangular wave signal reaches a peak edge. A second high-side transistor is turned on in a third period until the triangular wave signal reaches a bottom edge. A first low-side transistor and the second high-side transistor are turned on in a fourth period until the triangular wave signal reaches again the error voltage. The second high-side transistor is turned on in a fifth period until the triangular wave signal reaches again a peak edge. The first high-side transistor is turned on in a sixth period until the triangular wave signal reaches again a bottom edge.

Inverter using PWM method

A dc-ac converter capable of supplying a finely regulated ac drive voltage to a load is provided. For this purpose, the converter includes, in a primary winding of a transformer, a full-bridge or half-bridge type semiconductor switch circuit whose switch can be controlled by pulse-width modulation. Transformer has a secondary winding for connection with a load. Based on PWM signals and by use of adequate switching logics for controlling multiple semiconductor switches, sophisticated control including zero-current switching and penetrating current prevention can be effected. Moreover, by means of regulated burst control of the ratio of on-duty period to off-duty period together with pulse-width modulation control, power supplied to the load can be regulated over a wide range beyond the limits of control obtained by the pulse-width modulation.

DC-AC converter and method of supplying AC power

Primary and secondary regions are electrically insulated from each other. The first and second pulse transformers are provided to the respective transistors in the switching circuit. Secondary windings of the first and second pulse transformers are connected to control terminals of the transistors. The control circuit supplies switching voltages to primary windings of the pulse transformers based on a feedback signal fed back through a feedback line. A primary winding of a transformer, the switching circuit, and the secondary windings are disposed on the primary region. A secondary winding of the transformer, the primary windings, the feedback line, and the control circuit are disposed on the secondary region.

Growing community of inventors

Kyoto, Japan

Kenichi Fukumoto