subject: Lighting LEDs on mains and Resonant asymmetric inductive supply [print this page] Lighting LEDs on mains and Resonant asymmetric inductive supply
LEDs, by nature, require direct current (DC) with low voltage, as opposed to the mains electricity from the electrical grid which supplies a high voltage with an alternating current (AC). where to buy cheap LED Strip? Lightereryday is a good choice.
A CR dropper (capacitor and resistor) followed by full-wave rectification is the usual electrical ballast with series-parallel LED clusters. A single series string minimizes dropper losses, while paralleled strings increase reliability. In practice usually three strings or more are used. An advantage of a capacitor is that it can reduce the high line voltage to an appropriate low voltage, without wasting power, with a very simple circuit; a disadvantage is that there may be a high surge of current for a short time when it is first turned on.
Operation on square wave and modified sine wave (MSW) sources, such as many inverters, causes heavily-increased resistor dissipation in CR dropper, and LED ballasts designed for sine wave use tend to burn on non-sine waveforms. The non-sine waveform also causes high peak LED currents, heavily shortening LED life. An inductor and rectifier make a more suitable ballast for such use, and other options are also possible. Dedicated integrated circuits are available that provide optimal drive for LEDs and maximum overall efficiency.
Multiple LEDs can be connected in series with a single current limiting resistor provided the source voltage is greater than the sum of the individual LED threshold voltages. Parallel operation is also possible but can be more problematic. Parallel LEDs must have closely matched forward voltages (Vf) in order to have equal branch currents and, therefore, equal light output. Variations in the manufacturing process can make it difficult to obtain satisfactory operation when connecting some types of LEDs in parallel.
To increase efficiency (or to allow intensity control without the complexity of a DAC), the power may be applied periodically or intermittently; so long as the flicker rate is greater than the human flicker fusion threshold, the LED will appear to be continuously lit.
RAIS is an off-line LED driver topology with TRIAC dimmer compatibility and near unity power factor with no loss in efficiency.
This LED driver technology is especially suited to use with domestic TRIAC dimmers. Resonant asymmetric inductive supply (RAIS) sits between the mains and the LED. Report L10270 from the Lighting Association Laboratories found that the technology would work across different dimmer types while still maintaining a power factor of 0.96, and with an input to output system efficiency of 91 per cent. As the light is dimmed, the system is able to hold a significantly higher efficiency than a Buck converter as RAIS draws a continuous current without using bleed resistors. RAIS is a single stage supply that also delivers a constant current output to the LED with no sense resistor. The report also found that RAIS technology fitted into the dimensions of a standard GU10 lampholder (bayonet mount). recommend directory: 3528 SMD Flexible Strip with waterproof 5 Meter 150 LEDS.
LED lighting typically involves LEDs connected in series. The resultant forward voltage may be in the region of 10 to 20V. In such cases, the ratio between the mains voltage and the voltage required to drive the load is between 10 and 20. With such a large ratio, conventional circuits used to drive LEDs become very inefficient because the switching will be operating at extremes of duty ratio with very short conduction times and high peak currents. This inevitably means that extra components, such as a common mode choke, need to be used. It is therefore common to include a magnetic or piezoelectric (ceramic) transformer with an input-to-output ratio suitable to create a step down in voltage and a corresponding step up in current, introducing further efficiency loss, cost and bulk.
In contrast, the RAIS technology can drive high current, low voltage LED strings from a 240V AC mains supply without high peak currents, a transformer, or common mode choke, and still achieve the turns ratio.
Typical Use: Between the mains and the LED within retro fit lamps, such as a GU10, where small size and use with conventional TRIAC dimmers is required.
Special Features : Inherent compatibility with a TRIAC dimmers through continuous current draw in the same way as a conventional lamp, in other words it looks like a resistor to the mains. This also has an impact on the efficiency as it does not require a bleeder circuit or holding current resistor to ensure proper TRIAC operation that can cause efficiency loss during dimming.
The topology is inherently constant current. There is no need for a second stage, current sensing, feedback or short circuit protection.
Typical performance of a TRIAC dimmable LED retrofit lamp, Power Factor 0.96, efficiency > 90%.
The RAIS technology has now been granted UK patent # GB2449616 dated 17th February 09 and is applied for in most other world-wide territories. recommend directory: 3528 SMD Flexible Strip with Non-waterproof 5 Meter 300 LEDS.
