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  1. KrisBlueNZ

    Constant current regulation with boost converter, PWM and 555 timer.

    Yes, that's what I think. I didn't agree with Fish about the MOSFET being a high-side switch. It clearly isn't, and the converter is a standard boost converter. And you're not the first person here to want to use a 555 to control a high-power converter. But in the fight between "it's not...
  2. KrisBlueNZ

    Chicken Coop Door Opener

    That transformer looks fine. The slightly high mains voltage won't be a problem. You should connect the secondaries in parallel.
  3. KrisBlueNZ

    Nand Gate oscillator help

    One side of the speaker (the red wire) is connected to the emitter of the transistor. That's right. Where should the other side of the speaker be connected to? Also there is a yellow link wire from the emitter of the transistor to one of the power supply rails. It shouldn't be there. You may...
  4. KrisBlueNZ

    Solid State Trigger Coil Simulator

    How do you want to improve it? Do you want to make it simpler? Do you want to make the output pulse shape more accurate? If so, post a picture of what it should look like.
  5. KrisBlueNZ

    check the circuit

    If you tell us what the circuit is supposed to do, we might be able to tell you whether it's correct or not...
  6. KrisBlueNZ

    Portable mobile charger

    This data sheet has some good guidelines: http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf http://www.google.com/search?q=how+to+use+7805+regulator
  7. KrisBlueNZ

    surveillance equipment

    Sounds more like it's haunted... ;-)
  8. KrisBlueNZ

    12V - 350V 200mA converter for motorcycle CDI

    And it's only the transformer that's getting hot? Could be, but I doubt it. There's a lot of base drive available from the transformer. I think it's more likely a standard BJT. Do you still have the original transistor? Does it still work? You can measure the base-emitter voltage using a...
  9. KrisBlueNZ

    Constant current regulation with boost converter, PWM and 555 timer.

    The CMOS versions of the 555 have much lower output drive capability. You need a high current driver to charge and discharge the MOSFET's gate-source capacitance quickly. If you don't switch the MOSFET quickly, it will overheat because it will stay in its linear region too long. That is not the...
  10. KrisBlueNZ

    No Color. Black and White Picture

    Check the components and tracks in the path from pin 8 of the chroma IC to the flyback transformer. On that schematic they are R824 and R825, fed from pin 8 of the flyback. If that's all OK, I don't know what else to suggest.
  11. KrisBlueNZ

    High Amperage Power MOSFETs

    Hi Aaron and welcome to Electronics Point :-) The maximum continuous drain current relates to when the MOSFET is saturated, i.e. VDS is very low. As soon as VDS starts to rise, power dissipation in the MOSFET starts to rise very quickly. It's only because MOSFETs have such a low RDS(on) that...
  12. KrisBlueNZ

    -1kV pulse generator

    Um... I can't give you any specifics, I'm afraid. If I was going to do this, I would get a range of cores, a few reels of wire, and some high-voltage pulse-withstanding capacitors around the 1~47 nF range, and do some experimentation.
  13. KrisBlueNZ

    No Color. Black and White Picture

    Who is the manufacturer of the chroma IC? Do you have a data sheet for it?
  14. KrisBlueNZ

    12V - 350V 200mA converter for motorcycle CDI

    One other thing. Can you add a good-quality 1 µF 50V capacitor e.g. a film cap, as directly as possible between the top side of the primary and the emitter of the transistor. Just to give the transistor a nice clean low-impedance source to work into. Something like...
  15. KrisBlueNZ

    12V - 350V 200mA converter for motorcycle CDI

    Sorry for dropping out of the thread! Steve is doing a good job though. I really want to see a primary current waveform! The way you did it before, with a series resistor between the transistor's collector and the bottom of the primary, is not a good idea, because there are high-voltage spikes...
  16. KrisBlueNZ

    Combining an Amplifier with a Voice Changer?

    Bummer :-( Voltage across the C diode should be at least 4.2V with power turned ON. If it's not, and everything is connected exactly as before, either the C diode is short or, more likely, the voice processing IC under the tarry blob is dead. That's interesting that the amp works with the...
  17. KrisBlueNZ

    Help with using a 7404

    The module will detect the state of the switch according to the voltages on its inputs. If it needs to see "ground or nothing", then it has internal pullup resistors so that when a switch is open, its voltage is pulled up. This allows it to distinguish switch closed (input pulled to ground...
  18. KrisBlueNZ

    Help with using a 7404

    You can turn a standard BCD switch into a complementary switch by connecting its common terminal to the opposite supply rail. Pullup or pulldown resistors may also be needed.
  19. KrisBlueNZ

    What is BV in LDO datasheet?

    True, the 7805 is definitely not an LDO. And dhlee said that "BV" is not on the data sheet; it's in a comparison on a Powerpoint slide. I'm suggesting that the author of that slide might have meant "breakdown voltage".
  20. KrisBlueNZ

    Constant current regulation with boost converter, PWM and 555 timer.

    It's a boost converter. I agree, I don't think a 555 is a good control device. Google for designs based on the UC3842/3/4/5 current mode controller. It's normally used in isolated flyback applications but a boost converter is almost the same as a flyback converter without isolation. True dat.
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