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  • Users: grigson
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  1. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    Thanks, My math is in pounds and pence, and we have done it the cheapest way. Our product range is for architectural use and often only used for one TV set, or for one poccasion/dinner/party etc. ..but still we'd like to have longevity in the product as well as their prettiness. The power...
  2. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    IRStuff: ......there's still going to be convection into internal ambient....which transfers heat through the plastic & perspex enclosure to external ambient....i admit its not a great heat transfer path, but its all we have. IRStuff ....When you say that, do you mean that we should make...
  3. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    sorry forgot, by the way, there is NO thermal test data on this product. It has past EMC testing, but no thermal testing has EVER been done.
  4. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    -thanks Sorry Operahouse, this product was designed by another engineer in the company who is now working on a different project. -I was simply asked to change a transistor to a cheaper variety on the schematic, -but looked at the product, and noted the lack of "bare" , uncovered aluminium...
  5. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    LEDs temperature rated to 120C junction.....they are 1W LEDs as i said, but actually its flashing, so, in fact, each of the twelve leds is dissipating 0.6W. We cant put holes in the enclosure as condensation would get in. Our margins are too tight and we cant afford hollow aluminium bar. I...
  6. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    its till worth convecting heat into the internal ambient, so that the warmed air can flow against the perspex enclosure and transfer heat to it, which will then conduct through the perspex, and then convect from the outer perspex surface to the external ambient. So we need to get an internal...
  7. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    the product is enclosed in a plastic and perspex case, so thers no convenient "somewhere else" for the aluminium bar to conduct the heat to. Our application is constant power, with no transients. VE1BLL... You appear to be saying what i am not brave enough to say.........that in fact the...
  8. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    Operahouse .....the option of having four copper clad PCBs with no aluminium in the middle does effectively form a hollow metal tube......the metal being provided by the backs of the PCBs. Otherwise, a hollow aluminium tube actually costs more than a solid one, since it takes more work to get...
  9. grigson

    Cooling LEDs?....Bigger volume of metal, or bigger surface of metal?

    Hello, We have four narrow rectangular LED PCB's, each one comprising three 1W LEDs. These are double sided PCB's with thermal vias to the bottom layer. Each PCB is mounted on one of the four faces of a vertical, solid aluminium bar...so we have light shining North, East, South & West from...
  10. grigson

    LEDs in parallel -no problems?

    Hello, My company has been putting 1A power LEDs from Cree and Osram in parallel for soome time now. We only ever use a single current source, and NEVER use series current equalisation resistors or current mirrors. We have encountered no problems......so why is everyone telling us we are...
  11. grigson

    Linear current regulator with pulsating 3.2A input current is bad?

    Thanks: Comcokid, ..yes but surely the turn on time is a small , tiny interval, and will not be significant in heating the LM350? When flash is on, the LM350 has 28 - (7.5+1.25 + 3.2*3.9) across it = 6.77V When flash is off, the LM350 has nearly 28V across it ..but its not conducting...
  12. grigson

    Linear current regulator with pulsating 3.2A input current is bad?

    Hello, We are in Brisbane and are having big trouble (and angry customers) with a 6.8W flashing LED light which is a warning light………… The linear regulator (LM350) keeps blowing up (its case is blown wide open). Here is the schematic. http://i48.tinypic.com/2cfxwqq.jpg (the schematic uses...
  13. grigson

    Why high voltage supply rails for class D amps?

    Hi, Why do Class D amplifier designers prefer high voltage supply rails? Please find attached here two Full-Bridge , Class D amplifier simulations which run in the free simulator called LTspice by linear.com. Each simulation is of a 4KHz sine wave which gives 100W of power in the speaker...
  14. grigson

    Likely value of Cpole for optocoupler?

    We understand how to measure it, its just that part to part variance is said to be extremely wide, and if we measure it on one part, we've still no idea what is the min and max of any particular batch. We are in Vancouver and the semiconductor/component reps dont get up to us much too.
  15. grigson

    Likely value of Cpole for optocoupler?

    hello do you know what are likely values of the Cpole parameter for this optocoupler? CNY17-2 http://www.vishay.com/docs/83606/cny17.pdf I am talking about when there is round 3mA flowing in the opto diode. I need the full tolerance range....i.e min and max of Cpole. This optocoupler will...
  16. grigson

    Method of Measurement of average current is accurate?

    Hello, Please can you tell if our method of measuring a 500KHz triangular current waveform is accurate? We are just measuring the voltage across a series sense resistor. This is the shape of current waveform we are trying to measure the average value of:- http://i39.tinypic.com/2vwsht1.jpg...
  17. grigson

    Flyback with "active" clamp is OK?

    In comparison to Bridge's and Forwards....i found the flyback, at the same frequency and the same V(in), has essentially the same peak primary current, and the same RMS input current as the bridge and the forward. (as you know, it depends on the Lp for each, but basically they can be the same)...
  18. grigson

    Flyback with "active" clamp is OK?

    There are four sacred laws that i look for in a smps design:- Thou shalt not overvoltage. Thou shalt not overcurrent. Thou shalt not overheat. Thou shalt pick the cheapest. and obviously there's EMC to pass, and whatever regulations apply. The usual sacred laws of small Size, efficiency and...
  19. grigson

    Flyback with "active" clamp is OK?

    Too be honest, its just a little better than the mains transformer that it replaces......but a lot better than that because the mains transformer only gave our required V(out) from a specific V(in). This is an amp for a 6-string guitar, and not for a bass guitar. We have introduced...
  20. grigson

    Flyback with "active" clamp is OK?

    Single switch forward i did not like because at switch-off, the drain voltage shoots up to 2xvin + leakage spike......and that really is a very high voltage, with a corresponding high switch-off switching loss. Forwards also need an output inductor, (or rather two in our case because output is...

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