Simplified luminaire design with LED modules
Acrich 2 modules from Seoul Semiconductor are designed for general illumination and are intended to be connected with 2 leads directly to the AC network without any further rectification needed. The incorporated IC, designed especially for the optimized drive of each individual LED, allows the lack of a separate ballast or rectifier. This space saving concept gives the designer a new freedom for the layout of his product.
Applications of the module start from modern luminaries to complex illumination systems but also conventional replacement bulbs and tubes. Benefits of the Acrich 2 are reduced weight, high life time, high efficacy and good power factor which gives tremendous long term potential for power savings in many illumination application.
Integrated driver concept
The drive circuit on the Acrich 2 modules consists of an IC generating the necessary current for each LED directly out of the AC without using a rectifier. Depending on power class the IC has 4 or 8 output channels which are directly connected to the LED. Each output channel is activated separately by the IC. The IC comprised all diodes and passive components and is therefore a simple and effective LED solution for the design of luminaries. As there is no need for life time limiting components like electrolytic capacitors the driver circuit does not limit lifetime. The AC synchronic drive of the LED reduces the noise level on the connection cables. In normal operation mode no further components are necessary to stay below the allowed noise level. This keeps the cost low. The human eye does not observe any flicker and many standard Dimmers can be used without problems.
Image 1: Drive principle and current level in relation to the AC input Voltage
Image1 shows the basic trigger circuit and the current level in dependence of the phasing AC voltage. For which LED the current is turned on from 0 to 180 shows the table below.
Acrich IC is designed for the standard network voltages
The Acrich2-IC is available for AC drive voltages of 90 – 120V (100V) / 100 – 144V (120V) / 200 – 264V (220V / 230V / 240V) and a nominal output power of 4 and 8 Watt. Based on that product range the typical AC drive voltages all over the world can be addressed. Power factor is 90%, lifetime with a minimum of 87.000h. The max. junction temperature is specified with Tj = 125°C, operating temperature Topr -30 to 100°C and a storage temperature of Tstg -40 to 120°C.
Image 2: Circuit configuration and mechanical appearance of the 4 Watt module (230V.)
Image 3: Circuit configuration and mechanical appearance of the 8 Watt module (230V). For full resolution click here.
Image 2 – 4 show the electrical circuit and the mechanic appearance of the 4, 8 and 12 module (230V DC). Meanwhile a 16W module has been launched.
Further safety precautions
Driven under the usual operating conditions of AC networks Acrich 2 modules do not require further safety precautions. If driven in AC networks with high voltage peaks e.g. in industrial areas with heavy inductive loads (motors), further safety precautions for the high voltage sensitive IC are necessary. For that purpose a metal oxide varistor (MOV) who keeps the short time electric energy is connected in parallel to the connection leads. A resistor R (22 Ohm, 1 Watt) works like a safety fuse when to much energy hits the IC (image5). The function of the protection circuit can be tested in the lab according the surge test IEC 61000-4-5 and the ring wave test according IEEE C.6241.
Image 5: Surplus protection circuit when Acrich modules are driven by AC net showing voltage peaks or danger of lightning
Driven under the usual operating conditions no further EMI protection is necessary. If the Acrich 2 module is used in an EMV sensitive area, like in laboratories or near to electromedical instruments, a suppression capacitor C on the connection leads will reduce the level of interference. The component (10nF, 630V) has to be an induction reduced metal film ceramic capacitor (image 6).
Image 6: Surplus suppression capacitor only has to be used in EMV sensitive surrounding
Protection against contact
While designing a light fixture the designer has to consider that no hot components are unprotected and touchable by the user. The red circle in Image 7 shows the connection pads of the module which are contacted direct to the AC network. It is recommended to cover the connection pad after soldering of the leads with some protection against contact. Possible materials could be silicon, epoxy or another isolating material. Further more wires have to be protected against damage with e.g. a silicon isolation tube.
Image 7: Connection pads with protection against contact
Operation with electronic dimmers
Standard electronic dimmers utilize phase modulating dimming through TRIAC switches and are designed for conventional incandescent lamps. The thermal inertia of the filament allows the continous variation of brightness although this is a type of pulse width modulation of the AC net voltage. When using electronic dimmers the overlap of phase cut and pulse width modulation can cause malfunction which leads to heavy flickering and reduced maximum brightness. Based on the AC syncronic switch mode of the Acrich IC such problems do not occur. During tests with some dimmers, like the Busch-Jaeger (6513U-102) GIRA (030700) or Merten (577199), it can be observed that the LED module can not be dimmed down completely, a marginal brightness is kept (Image 8). Normally, especially for private users, this effect is tolerable.
Image 8: Dimmer performance of a 100 W triac dimmer comparing the 8W and 12W module with a conventional 40W incandescent lamp
About the author: Lorenz Bauer is Senior Field Application Engineer for Seoul Semiconductor.
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