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 (Image 5
). 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.
This article was first published on EE Times Europe.
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