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Recent content by gijim

  1. gijim

    Simple fail proof overtemp protection

    If the transistor gets shorted on though, disconnecting the base won't do anything.
  2. gijim

    Simple fail proof overtemp protection

    BobM3 - thank you! They have one rated at 6 amps that should work well if epoxied to the transistor and/or heat sink. I will try to find a distributor. xnuke - thanks! That's certainly another option to look into.
  3. gijim

    Simple fail proof overtemp protection

    Thanks. Ideally if a thermal switch is used, it should be PCB mount (like the to-220 one) I think the polyswitch won't work; I haven't seen one that can handle both the voltage and the current (1-2A@90 up to 240Vac)
  4. gijim

    Simple fail proof overtemp protection

    I've got an AC circuit that draws about 2A. What I need to do is cut the power to the device should a transistors heat sink overheat (defined as >100C). Preferably until the user unplugs the unit, or at least until it cools down some amount (20C?). It should be resettable, not permanent...
  5. gijim

    Thread forming screws

    Excellent, thank you! I guess I must have been looking at sheet metal screws or something.
  6. gijim

    Thread forming screws

    I'm not very familiar with thread forming screws (not to be confused with thread cutting screws) How do you find the appropriate drill size for these? I want to attach two thick aluminum plates together, quickly, without having to tap holes. They seem like the best method, but these "odd"...
  7. gijim

    120V 0.7A Constant current source

    Okay, buck boost is bad....... I don't want it blowing up if the load went open circuit. How do I use two strings of LED's at half the voltage (~50V) with one buck converter? Suggestions?
  8. gijim

    120V 0.7A Constant current source

    Because according to another app note, you can only use the buck converter if your Vin > 2*Vout. Obviously in my case Vin~Vout, so the buck-boost converter has to be used.
  9. gijim

    120V 0.7A Constant current source

    Well the HV9910 will let me get by with about 10 parts. I have a question about ESR though... The ap note wants a 12uF low ESR (tantalum or ceramic) cap on the output. Since my output is >130V, that's a costly proposition. They don't make them, so I'd have to build it out of about $50 worth...
  10. gijim

    120V 0.7A Constant current source

    Wow, the actual design of a switching power supply is a bit over my head, but they have a really good app note that walks you through it. Thanks!! (I'll have to search to see if there are similar premade solutions... I'd like to get this up and running soon)
  11. gijim

    120V 0.7A Constant current source

    Well if you wanted to get concise, yes! ;) Can you suggest a switching supply with current control off the top of your head? The only ones I knew existed were straight forward fixed voltage..
  12. gijim

    120V 0.7A Constant current source

    Sorry, I always tend to muck descriptions up.... It's a diode array that will be powered by mains (120V) voltage. Problem is there is a wide range of voltage tolerance on these devices... Nearly 100%. So these devices will need "somewhere" between 76V-120VDC..... But 0.7A is their maximum...
  13. gijim

    120V 0.7A Constant current source

    Here's the problem.... I have a load that varies from 76 to 120VDC, but always needs a constant 0.7A. I figure "okay, no problem, just need to rig up a constant current source for 120Vac use".... In the interests of keeping costs and parts counts low, I decided an NPN current source might be the...
  14. gijim

    When is an LED hazardous to your eyes?

    Is there a way to calculate the danger like they do with lasers? I have 18 watts worth of LED's in a reflector. I know it is extremely bright, and looking at it directly for a split second will cause "floating images" in my vision for a few minutes. So I know it's not good to look at, but...
  15. gijim

    How does traction control work?

    It's hard on the engine in that you can burn up a valve if it hasn't been "calibrated". I'm assuming a race vehicle which does not have a catalyst, has a mechanical throttle, and the installer doesn't want to "calibrate" anything (or is inexperienced). The fuel cut seems to be the best of...
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