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  1. KrisBlueNZ

    220v LED DIMMER??

    That's true. But there are problems with that circuit. Specifically the way the gate supply voltage is derived, and with PWM over house wiring. I found the original circuit with its description, at http://www.extremecircuits.net/2010/06/dimmer-with-mosfet.html The description specifies...
  2. KrisBlueNZ

    Question about MOSFET

    Yes, 15R means 15 ohms. Yes that circuit would run from 5V, but not much less. You need to have enough voltage at the MOSFET's gate to fully turn it on. I don't know what you mean by current from a voltage regulator affecting the operation of the circuit. Here's a better design, without the...
  3. KrisBlueNZ

    220v LED DIMMER??

    OK, I'm glad you drew up the schematic of the LED lamp, because that design WILL NOT work from DC anyway! It uses the two 800 nF capacitors to convert the AC mains voltage into a current. If you supply it with DC, the capacitors will just charge up and the current will drop to zero. To dim...
  4. KrisBlueNZ

    220v LED DIMMER??

    Sure. What worries me are the things you may not know that you don't know. That's one reason why electrical safety inspectors exist! Actually a switching power supply lS a good approach. A linear regulator wastes significant power, which gets converted to heat. Here are a few ROUGH calculations...
  5. KrisBlueNZ

    Question about MOSFET

    Yes, a Schmitt trigger is needed. This design should do what you want. This circuit will work with any supply voltage from 6V to 12V. R3 and D2 and the emitter-to-source connection create hysteresis, the necessary characteristic of a Schmitt trigger that makes it switch cleanly. The voltage...
  6. KrisBlueNZ

    220v LED DIMMER??

    Looks like there are lots of possibilities on Digikey. Go to their product index and select "Integrated Circuits -> PMIC - AC DC Converters, Offline Switchers". Narrow down the selection using the input voltage range and the output power rating, and by checking the "In Stock" box. Choosing power...
  7. KrisBlueNZ

    220v LED DIMMER??

    Oops! 100 mA at 300V is 30W, not 3W! So the Motorola app note I linked to might be the answer. Except that the NCP1052 is not available from Digikey. I suspect it's obsolete. But the app note might give you some ideas. Also have a look at the other search results.
  8. KrisBlueNZ

    220v LED DIMMER??

    You would need a switching regulator that would operate from 350 VDC! In other words, a mains-powered power supply with an output that can be varied over a wide range, and doesn't need to be isolated from the input. Try Googling high voltage buck converter power supply The first hit looks...
  9. KrisBlueNZ

    A431 NPN THROUGH TRANSISTOR

    BTW the generic part number for the device is TL431. It was originally made by Texas Instruments. It's readily available from various manufacturers, through Digikey, Mouser, etc.
  10. KrisBlueNZ

    Question about MOSFET

    1. Your schematic has a curved line from the 9V supply rail coming down to the ADJ pin of the regulator. I don't know what it's supposed to mean. It shouldn't be there. 2. Is your 9V battery the "PP3" type? That's the kind that's about the size of two AAs with a snap-on connector. These...
  11. KrisBlueNZ

    220v LED DIMMER??

    My guess would be that at a high duty cycle, you would see no dimming of the LED, and at low duty cycles, the LED might go out, or blink. It really depends on what's inside the LED light bulb. At very high duty cycles the circuit will stop working properly and I couldn't predict exactly what it...
  12. KrisBlueNZ

    A431 NPN THROUGH TRANSISTOR

    Excellent reply, davenn!
  13. KrisBlueNZ

    220v LED DIMMER??

    The circuit in your first post has a number of problems and I wouldn't use it. Also it probably won't dim an LED light bulb. It depends how the LED light bulb is designed internally. If it contains a rectifier and capacitor, PWM control won't vary its brightness. Nor will phase angle control...
  14. KrisBlueNZ

    Touch switch help!

    You started this thread with a touch switch that works by finger resistance, using two pads. This design works by noise pick-up. There are other methods. Have you done a thorough Google search? Try keywords touch switch methods techniques design. Your original design using the Darlington...
  15. KrisBlueNZ

    Touch switch help!

    Those component values look OK. The circuit relies on pickup of mains hum and other noise. When the pad is not touched, the 10M resistor keeps Q1 biased ON, which keeps Q2 turned OFF. When you touch the pad, Q1 doesn't turn completely OFF; what happens is that Q1 turns OFF briefly each time Q1's...
  16. KrisBlueNZ

    Resonance

    Are you for real? Or are you a... BTW I can tell you how to save money on your electricity bill using a crystal radio. 1. Turn off all the appliances in your house. 2. Build a crystal radio receiver. 3. Connect it to the mains supply. 4. While grasping an earthed water pipe with one hand...
  17. KrisBlueNZ

    Trapezoidal Wave Generator Circuit

    The best way to do that is to generate a fixed frequency using an astable multivibrator or any type of oscillator, and feed it into an adjustable monostable. The monostable period, as a percentage of the oscillator period, determines the duty cycle percentage. The frequency will not vary as the...
  18. KrisBlueNZ

    Common FETs

    Futurelec have a wide range of JFETs! Wider than Digikey or Mouser. That seems reasonable to me, but that's not an area I have much experience with. I guess you could Google JFET audio designs and see what other types have been specified. BTW when I asked where you live, I was trying to imply...
  19. KrisBlueNZ

    Common FETs

    I guess you'll be wanting JFETs. I would see what low-power audio JFETs are available from the company you're buying from. Which company is that? And where do you live? There aren't many different types of N-channel small-signal JFETs to choose from.
  20. KrisBlueNZ

    how test an optocoupler?

    http://www.google.com/search?q=how+to+test+an+optocoupler
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