Fullscreen HTML5Med Res (??MB)HTML4

Advertising Index Advantage Partnership Lawyers... 95 Altronics....................................... 17 element14...................................... 5 Emona Instruments........................ 3 Harbuch Electronics..................... 10 Hare & Forbes.............................. 39 High Profile Communications....... 95 Icom Australia................................ 7 Ask SILICON CHIP . . . continued from page 94 (Samsung 13W chip) down-lights using Tenico UP-15W-D constant current dimmable LED drivers. The dimmer will be a Clipsal trailing-edge variety. All of this is said to be fully compatible by my electrical wholesaler. I have set it up as a test rig and all seems to function correctly. What did surprise me is the “blinding” brightness when the dimmer was turned full on; I was half expecting to see smoke! I then studied the specs of the lamps and the drivers and this is where I became confused. The lamp spec quotes: voltage 26-30V DC; current 320mA; power 13W; colour 3000K. The Driver spec quotes: constant current dimmable LED driver; primary 200-240VAC <at> 0.11A; secondary DC 23-38V 320mA ± 5%; dimmable with leading/trailing edge or universal dimmer. The variable DC requirement of the lamp and output of the driver is what confuses me. Is this to do with the constant current requirement of the LEDs? If so, then how is the output voltage controlled so that the current control is correct for the lamp involved? In my case it would appear that for the lamp to generate its full 13W output at 320mA, the voltage would need to be 40.6V. So why does my lamp quote a maximum rating of 30V <at>320mA which is only 9.6W? Conversely, as my driver can supply 320mA <at> 38V, does this mean that I can overdrive the lamps leading to earlier failure? Then of course one can bring the dimmer into the equation and I am lost! It would be really good to have an article on this subject so that the mystique of LED lamps, drivers and dim96  Silicon Chip DOWNLOAD OUR CATALOG at www.iinet.net.au/~worcom WORLDWIDE ELECTRONIC COMPONENTS PO Box 631, Hillarys, WA 6923 Ph: (08) 9307 7305  Fax: (08) 9307 7309 Email: worcom<at>iinet.net.au Jaycar .............................. IFC,45-52 Keith Rippon ................................ 95 KitStop.......................................... 11 LED Sales.................................... 95 Low Energy Developments.......... 95 Master Instruments...................... 95 Notes & Errata Nixie Clock, July 2007: the circuit diagram (Fig.1) shows pin 14 of IC1 connected to pin 12 of IC2. The connection should in fact go to pin 11 of IC2. The PCB layout diagram on page 73 of the August 2007 issue is correct. mers can be better understood. Failing that I would appreciate any comments you can make on my particular example. (M. F., Mount Eliza, Vic). •  Normally, LEDs are driven using a current source and the voltage developed across the series string of LEDs is dependent on the characteristics of the LEDs. These have a higher voltage across them with higher current, ie, they have positive impedance. So the LED lamp specifications of 26-30V at 320mA refers to the fact that this is the range of possible voltage across the lamp (of in-series LEDs) when driven at 320mA. The voltage depends on the individual LEDs themselves and can vary from manufacturing batch to batch. The 26-30V refers to the specified limits that the LED voltage could be at that 320mA current. So long as it can deliver the required voltage range of 26-30V at 320mA, then the driver should be suitable and Microchip Technology............... OBC Mikroelektronika......................... IBC Ocean Controls............................ 29 Premier Batteries......................... 55 Quest Electronics......................... 95 Radio, TV & Hobbies DVD............ 11 RF Modules.................................. 96 Sesame Electronics..................... 95 Silicon Chip Binders..................... 95 Silicon Chip Bookshop................. 90 Silicon Chip Online Shop........ 88-89 Silicon Chip Subscriptions........... 81 Tekmark Australia........................... 9 Wiltronics...................................... 65 Worldwide Elect. Components..... 96 xLogic............................................. 9 it can drive the LED lamp correctly. The voltage across the LED lamp will settle at the voltage that allows 320mA current to flow. When dimmed, the average current is lowered by reducing the pulse width of the applied current so that the lamp receives less power. The power discrepancy may be that 13W is the total power of the LEDs SC plus the driver. siliconchip.com.au