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  1. C

    IGBT Half-bridge Module Help

    It depends on what you want to do. Basically the lower transistor is a common-emitter device and the upper transistor is an emitter-follower. This means you need to drive the upper transistor from a PNP transistor to turn it on and then you drive the PNP transistor via an NPN transistor. You...
  2. C

    Quick question about Amp/Speaker Wattage

    "18V AC or 24VDC" Yes, but he has only got 3 watt spkr and so the max voltage should be about 12v to 15v You can get the 3 watt stereo version for 70 cents with free postage and all the hassles are over...
  3. C

    Need a super simple 3v DC timer circuit

    "I think Poor Mystic was talking about a common collector buffer where approx. 0.6 Volts is lost due to the Vbe junction." 0.6v doesn't even apply to an emitter-follower because the LMC555 does not go rail-to-rail and you lose another 0.3v. You don't think of using an emitter-follower when you...
  4. C

    Need a super simple 3v DC timer circuit

    "With a bipolar transistor, 0.6V is taken up by the base-emitter junction, which reduces the voltage available o drive the load." What rubbish. The collector-emitter voltage can be as low as 0.3v to 0.5v and some ZTX transistors can be as low as 0.05v.
  5. C

    Quick question about Amp/Speaker Wattage

    You need a 12v battery or plug pack. The plug pack can be AC or DC. The maximum voltage is 18v but you can use 12v AC or DC plug pack. You can use AC or DC and you can connect the wires either way to the board. This will give you a low wattage amplifier - just what you need.
  6. C

    Need a super simple 3v DC timer circuit

    A MOSFET needs at least 1.8v
  7. C

    Resistor value

    The instructor should not be teaching electronics. He gets 39% for setting the test. To give 25% for "good housekeeping" shows the instructor is short of questions. I have never asked or been asked such stupid questions. There are so many important aspects of basic electronics that have not...
  8. C

    Quick question about Amp/Speaker Wattage

    When the volume is turned down to a low output, the 3 watt speakers will only be seeing 1 watt. As you turn the wick up, you will see the cone move to its full excursion. That's as far as you can go.
  9. C

    Need a super simple 3v DC timer circuit

    You will need a buffer transistor as the chip will only deliver a few milliamp.
  10. C

    Resistor value

    What a terrible exam paper. Look at these stupidities: The resistance of a conductor involves BOTH the length and diameter. The two binary numbers - NONE of the above. Who has heard of a "resistance" meter???? How does a digital meter measure resistance???? Who wants to know ??? What are...
  11. C

    Need a super simple 3v DC timer circuit

    You will need 3 stages. Use BC338 in place of BD679 and motor goes in collector of BC338. Use 100u Remove diode and 1M and put switch in place of 1M. Remove globe.
  12. C

    Looking for a transformer. wonder if anyone could help

    It will be an auto transformer.
  13. C

    simple circuit drawing software

    I would go "one up" in font size and use 8pt for components and rectangles so you can fit the value inside the rectangle.
  14. C

    simple circuit drawing software

    "cant get any better than that and it prints so sharp!!" It is one pixel wide and you can write absolutely any value or comment without it getting fuzzy. I use Paint 6, only because I have been using it for 10 years and I sometimes have to add to old diagrams and I know how to drive it...
  15. C

    60 watts to 50 watts

    A 60 watt power supply is not $50.00 but $1.77 including free postage. http://www.ebay.com/itm/Buck-Module-24V-12V-9V-5V-DC-to-DC-4V-38V-to-1-25V-36V-5A-Step-Down-Power-Supply-/271701783241?pt=LH_DefaultDomain_0&hash=item3f42b032c9
  16. C

    60 watts to 50 watts

    There is one slight problem that no-one has addressed. The 12v transformer will deliver more than 12v on NO LOAD and also more than 12v on a load less than less than 60VA. The input to your cooler is DC. The output of your transformer is AC. When 12v AC is converted to DC via a bridge and...
  17. C

    PNP transistor in CLass B push pull amplifier

    Here's one answer. The NPN drives a load and generally this load is a speaker and electrolytic in series. When the NPN transistor turns ON, it delivers current to the speaker via the electrolytic and during this time the electrolytic charges a small amount. When the PNP transistor turns ON...
  18. C

    8-Pin Development Board

    You can't bring up the point that "It was going to have an overlay" because the simple fact is: IT DOESN'T Use a mini trim pot with shaft. The whole circuit will take less than 100mA and the regulator will not get warm. Come back to me in 6 months, after you have created another 20 projects...
  19. C

    8-Pin Development Board

    As you become more adept at laying out circuits you will find that your layout is just a jumble. Place the LEDs near the pins that activate them and always start with the IC socket around the correct way. Place everything as close as possible to the way the circuit is laid out. Never use a 10...
  20. C

    what wattage value would I use for the resistors in this schematic

    Just use 0.25w resistors
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