Recent content by RobD

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  1. R

    Does anyone know about Pulse Width Modulation?

    3490? 3453? If I were using an rechargeable LI battery I would go with the 3453 because it would give a constant current over the total battery range.(buck/boost) The 3490 (buck) is an odd chip if you ask me because it is designed for 1 or 2 A As so there will be a point where the...
  2. R

    Multiple mosfets in parallel

    You have to watch the gate cap loading (Miller Effect) but it's done all the time.
  3. R

    What Digital Multimeter Do You Recommend?

    Bench HP34401A Field- The Flukes. You can get the older HP with the LCD display on Ebay for around $150.00 and it's a good deal. The 34401a will cost $500.00 to $600.00 but boy are they nice! HP sells them new for about $1200 to $1400 new. The good thing about the Flukes is their cust svc...
  4. R

    Decision time! NiMH or lithium ion?

    Steve, I build a comparator circuit (MIC842 single comp/ref) into my flashlights to sense when the L-Ion is at 2.7 volts. When it is it turns off my drive chip. Saves my expensive batts.
  5. R

    Constant Power Lux Driver Circuits

    Re: Driver ckt design question (constant power) Hi guys, A couple of things: I looked a the circuit quickly and was wondering if the 358 will drive the 617 fully. If you're heat sinking the 617 that means you're losing efficiency. What freq. is this circuit going at?
  6. R

    Solar Panel + DC/AC Inverter = ???

    I agree with Tweek get a gel cell.
  7. R

    Rechargeable Li-Ion to 1W Stars

    Well, I'm really pulling my hair out trying to get high efficiency (88% or better) using the stars with Li-Ions (2.7 to 4.2 volts). I've come close but the best I can come up with is a boost over the 4.2 volts and not a buck/boost circuit. So essentially I'm boosing the batt. to a constant 4.5...
  8. R

    Variable Power Supply from a Wallwart ? Possible?

    Re: Variable Power Supply from a Wallwart ? Possib It is possible but not as easy as it looks. If you use a three terminal regulator there is something called insertion loss. (Most regs you buy at RS are the standard 317 series and the loss = 1.2 volts. The problem is going down to zero volts...
  9. R

    Undersize solar panel charging Li-Ion?

    I don't advise it. Here's why. Li-Ion batteries need a very specific charging cycle and they have to be held at the fully charged voltage for a specific period. Not following the manufacturers specs means shorter battery life. The best solution in any case is to use the designated charging chips...
  10. R

    Great little 1W luxeon driver circuit

    330ma is for 1 watt. You can run your 800ma too. Also don't run the Li-Ion down to 2.5 volts it's to low for good battery recovery. I run it down to 2.7 and then switch the circuit off with a 339 comp. Rob
  11. R

    Great little 1W luxeon driver circuit

    You can get away with SEPIC on buck or boost but not both in the same circuit. The problem with up/down SEPIC is efficiency losses. Most cases expect about 75%, give or take. The 'H' bridge will run boost with current sensing and limit so it always has high enough voltage to create the 3.4 volts...
  12. R

    Great little 1W luxeon driver circuit

    I'm beginning to think the only way to get any efficiency is with an 'H' bridge when using Li-Ion batts. A fully charged Li-ion is 4.2 volts if charged correctly. I'm working on a circuit to run constant current (330 ma) from 4.2 to 2.7 volts. At 2.7 volts the light shuts off to protect the...
  13. R

    New constant-current, constant-voltage LED driver

    Re: New constant-current, constant-voltage LED dri Yes and no. Mosfets are trickier than they appear. I like running 'N' types as high side switches using charge pumps to get the gate voltage up to where the conduct fully. Check out the Micrel MIC5014. Saves a lot of parts but it isn't that...
  14. R

    New constant-current, constant-voltage LED driver

    Re: New constant-current, constant-voltage LED dri I took a quick look at the Linear chip and it the efficiency is anything to rave about. What I want is 90+ with constant current from 2.7 to 4.2 volts. Has anyone done it? I was thinking of an 'H' bridge with low rds(on) mosfets and without...
  15. R

    Solar Battery Chargers - any thoughts.

    While you can get a solar panel to charge batteries you will also need a charge controller to keep the batts from over charging, batteries and an inverter to convert 12 volts DC to 120 AC. If you just want to charge ni-cads I think they make small solar charges for this. RobD
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