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  • Users: grigson
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  1. 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...
  2. 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...
  3. 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...
  4. 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...
  5. 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...
  6. 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...
  7. grigson

    Flyback with "active" clamp is OK?

    Hello, I am designing a 330W flyback. (Vin = 180-373VDC, Vout = 80V, 4A) The problem is that at light load the RCD clamp dissipates about 2.8W. So i have come up with this switchable RCD clamp....... http://i43.tinypic.com/2h71de9.jpg Can you see any problems with this? Is it OK? Here is...
  8. grigson

    Flyback SMPS OK for 320W?

    Hello, We need to design an SMPS where efficiency is not that important. (its for a guitar amplifier) Max Load = 320W Vout = +/-40V at 4A Switching frequency = 66.7KHz. Vin = 385VDC. Can we use a Current Mode Flyback in Continuous Mode? The maximum duty cycle would be 0.25...
  9. grigson

    20W LED tube interchangeable with 20W fluorescent tube.

    Hello, We want to put a 20W LED tube into a socket for a fluorescent tube with a high frequency, switch mode fluorescent ballast driver. ...we dont want to remove the fluorescent ballast as it would be inconvenient. Are there any standard solutions for this? -we still want it to be quite...
  10. grigson

    Obtainign Bode plots for SMPS feedback loop?

    Hello, Is there any company, anywhere in the world, that can provide us with Bode Plots for the SMPS Feedback loop if we send them our SMPS schematic and the specification to which the SMPS is intended.? We would pay for this.
  11. grigson

    Resonating LC output of Full-Bridge SMPS?

    Hi, I was recently sacked from my job as a SMPS designer at a new start-up Class D amplifier company Was i sacked because my voltage mode, full-bridge SMPS with +/-40V rails would have resonated at the output LC resonant frequency when audio pulses at that frequency were drawn from it? It was...
  12. grigson

    Cross regulation vs Transient Response...SMPS for Audio ?

    Regarding Full or half bridge SMPS for audio, (with split +/- output rails) Does any reader know :- 1. What percentage of the output inductors should be coupled.? 2. How to get good transient response , in spite of having coupled inductors.? (-because coupled inductors improves...
  13. grigson

    Half-Bridge vs Full Bridge SMPS?

    I think that Offline Half-Bridge converters are a complete waste of time....am i right? The full-bridge is cheaper and better...... FET RMS current will be much higher with a half-bridge than a full bridge, and the half-bridge fets will need to be more pricey with bigger heatsinks. -this is...
  14. grigson

    Can off-the-shelf inductor handle skin effect loss?

    Hello Please could you tell if an off-the-shelf inductor will be ok for our requirement? Eg will this inductor be ok…. 2209-RC (47uH from Bourns.com) http://www.bourns.com/data/global/pdfs/2200_series.pdfhttp://www.bourns.com/data/global/pdfs/2200_series.pdf It is the output inductor on a...
  15. grigson

    Half-Bridge SMPS transformer seems too large?

    Hi, I am designing an offline Half-Bridge SMPS at 350W and Vin = 90-265VAC. (there is no PFC stage) I am finding that I need to use an ETD44 core , but this seems awfully large. -I am wondering if it is normal to allow the core to go into saturation (i.e. above 300mT during transients etc?)...
  16. grigson

    Nuisance tripping of mains fuse woth non-PFC SMPS?

    Hello, We are worried about nuisance tripping of our mains input fuse in our Offline 270W (at the output) SMPS which supplies a guitar amplifier Vin (min) = 90VAC and uses a voltage doubler mains rectifier. There is no Power Factor Correction stage, its just a half-bridge SMPS. The...
  17. grigson

    Why have Active PFC in Audio SMPS?

    Hi, I have just seen the datasheet for a 180W (peak) offline SMPS which comprises a single stage active power factor corrector... here it is, its the SMPS180 by Hypex...... http://www.hypex.nl/docs/SMPS180_datasheet.pdf I cannot , for the life of me, understand why Hypex have made a Power...

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