A ballast circuit suitable for driving an LED or similar load, comprises a primary switch mode converter, means for measuring a modulation, such as a phase cut, as used for dimming light levels, on an input AC supply, a current regulator positioned in series with the load, and a feedback controller for controlling operation of the switch mode controller based upon measured modulation levels. The feedback controller is adapted to interrupt normal switching of the switch mode converter if modulation levels detected lead to the ballast working at a lower than desired efficiency (deep dimming), or if voltage levels across the current regulator are higher than desired. The feedback controller may have a further feedback means for controlling switch mode parameters during lower levels of modulation (shallow dimming). The circuit allows large dimming levels to be achieved without generating appreciable light flicker in the load.

An arrangement for driving one or more light sources is provided. According to an example embodiment, the arrangement includes observing durations of active periods, wherein an active period corresponds to a continuous period of operating power being supplied to a driver apparatus, selecting one of a plurality of lighting programs for the driver apparatus in accordance with the observed durations of one or more active periods, wherein a lighting program defines the desired characteristics of light provided by the one or more light sources as a function of time for a subsequent active period, and controlling, in response to an active period, provision of operating power from the driver apparatus to the one or more light sources in accordance with the most recently selected lighting program.

The disclosure regards to drivers and driving methods for a LED string consisting of LEDs. The LED string and a current switch are coupled in series between a power line and a ground line. The power line is powered to regulate a signal representing a current passing through the LED string. An enable signal capable of switching the current switch is provided. Whether a predetermined event occurs is detected. When the predetermined event occurs, the enable signal is clamped to have a predetermined logic value, the current switch thereby being kept either open or short.

An LED luminaire comprising LED arrays, a buck circuit with a switching portion comprising a transformer, and an LED driving circuit comprising a feedback control circuit is used to replace a conventional luminaire with a severe temporal light artifact. The buck circuit with the switching portion is configured to generate a variable DC voltage with a low-frequency ripple associated with AC mains. The feedback control circuit is configured to feedback a mixed voltage and current control signal to the buck circuit with the switching portion to compensate the low-frequency ripple so as to regulate an LED driving voltage with a ripple-reduced LED current to drive the LED arrays with a flicker-reduced light emission that may protect users of the LED luminaire from possible health hazards such as seizures, headaches, eyestrain, reduced visual performance, migraines, etc.

An LED tube lamp having an LED unit is disclosed. The LED tube lamp includes a control circuit that selectively determines whether to perform a first mode or a second mode of lighting operation according to a state of a property of an external driving signal and a switching circuit coupled to the control circuit and the LED unit. When the control circuit determines to perform the first mode of lighting operation, the control circuit controls the second circuit in a manner such that the switching circuit maintains its on state to allow continual current to flow through the LED unit, until the external driving signal is disconnected from the LED tube lamp, and when the control circuit determines to perform the second mode of lighting operation, the control circuit controls the switching circuit in a manner to regulate the continuity of current to flow through the LED unit by alternately turning on and off the switching circuit.

An LED tube lamp includes a lamp tube receiving an external driving signal; a rectifying circuit rectifying the external driving signal to produce a rectified signal; a filtering circuit filtering the rectified signal to produce a filtered signal; an LED lighting module comprising a driving circuit and an LED module, the driving circuit, in a first driving mode, receiving the filtered signal to produce a first driving signal for driving the LED module to emit light; and a mode switching circuit receiving the filtered signal as a second driving signal in a second driving mode for driving the LED module to emit light. Wherein, the first driving mode and the second driving mode are determined based on the external driving signal.

An LED tube lamp is disclosed. An installation detection circuit is configured in the LED tube lamp configured to receive an external driving signal. The installation detection circuit is configured to detect during one or more pulse signals whether the LED tube lamp is properly installed on a lamp socket, based on detecting a signal generated from the external driving signal. The installation detection circuit includes a switch circuit coupled to the pulse generating circuit, wherein the one or more pulse signals control turning on and off of the switch circuit. The installation detection circuit is further configured to: when it is detected during one or more pulse signals that the LED tube lamp is not properly installed on the lamp socket, control the switch circuit to remain in an off state to cause a power loop of the LED tube lamp to be open; and when it is detected during one or more pulse signals that the LED tube lamp is properly installed on the lamp socket, control the switch circuit to remain in a conducting state to cause the power loop of the LED tube lamp to maintain a conducting state.

An LED driver circuit and a method prevent LED turn-off flash when input power is lost to the driver circuit. The driver circuit includes a DC-DC converter that provides an LED drive voltage to an LED load. A voltage drop sensing circuit detects the loss of input power and discharges a filter capacitor that provides operating power to a controller in a DC-DC converter. The controller turns off to halt the operation of the DC-DC converter before the voltage provided to the LED load decreases to a turn-off threshold of the LED load. The DC-DC converter cannot recharge a load capacitor across the LED load. Thus, once the LEDs in the LED load turn off, the LEDs remain off until the input power is restored.

Light sources for replacing fluorescent lamps comprise light circuits with light emitting diodes, first and second terminals located at first and second ends of the light sources for exchanging first signals with high-frequency ballasts, and converter circuits for converting the first signals into second signals for feeding the light circuits. The converter circuits comprise reactive circuits for matching the light circuits and the high-frequency ballasts and provide safety to persons when installing the light sources. The light sources may further comprise protection circuits for protecting parts of the light sources against problems. The protection circuits may comprise monitor circuits for monitoring parameters of the light sources and for in response to monitoring results short-circuiting outputs of the converter circuits, and fuses. The reactive circuits may comprise protecting capacitors.

An LED driving circuit, a light tube and an illumination device are provided. The LED driving circuit includes a first AC input end, a second AC input end, a driving module, a first protection unit, a first DC output end and a second DC output end. The first protection unit includes a voltage detection subunit and an abnormality cutoff subunit, and the voltage detection subunit is connected in parallel between two corresponding voltage nodes of the driving module, and the voltage detection subunit is configured to detect a voltage value of the driving module; and the abnormality cutoff subunit is connected in series between the second input end of the driving module and the second AC input end; the first protection unit is configured to cut off a circuit of the driving module when a voltage abnormality of the driving module is detected.