| Electronics > Projects, Designs, and Technical Stuff |
| AC Rectified - DC Mosfet dimmer - Hints please |
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| BrianHG:
--- Quote from: bingo600 on March 02, 2017, 08:35:07 pm --- --- Quote from: Benta on March 02, 2017, 08:16:42 pm ---That circuit has so many dumb things, it's difficult to know where to start (is "instructables" really like that? I've never visited them). --- End quote --- Thanx for the comments I knew about the PWM source must be always on Author mentions this circuit (other creator) , and says it has some bad design faults , explains on Instructables page He modified it , and says this is better Unfortunately i'm an "Analog noob" , and "have to trust" the designers , that's why i asked for some hints (review) It will be in my summerhous , and i don't want a fire :scared: /Bingo --- End quote --- Yes, this is the schematic is what I was thinking of... |
| BradC:
--- Quote from: james_s on March 02, 2017, 10:21:03 pm ---Is there a reason for using such an unconventional circuit rather than the classic triac phase control dimmer? If you use a zero crossing signal to trigger an interrupt in your microcontroller it's fairly easy to adjust the trigger point. --- End quote --- The above circuit with the bridge rectifier in *series* with the load is a really neat way to allow you to use a DC device to control AC, so you can use a MOSFET rather than an IGBT. Additionally, it can be operated outside the parameters of being locked to a zero cross, so you can use either faster PWM *or* (as I've actually seen done) use the MOSFET as a resistor to give a clean but reduced voltage output (with the consequential power dissapation in the MOSFET). It'd even be a neat way of effectively implementing a trailing egde dimmer. I have a real issue with supplying high voltage DC to anything a finger can get into (such as light socket). |
| BrianHG:
You can also get rid of all the optocoupler and gate drive circuitry, replace it with a 500mw green led and a few photodiodes and a logic level mosfet. Good for switch on and off, isolated, but it wont work at high speed, but, you never need worry about the gate supply for that second circuit. |
| BrianHG:
Also, with the above AC circuit, a dumb 20Khz PWM allows for dimming of lights without the annoying 100/120hz buzz created by phase dimmers. Also, with a 20khz tuned inductor & cap filter, you can make a nice AC full sine wave of the source good for driving AC motors. |
| Zero999:
--- Quote from: bingo600 on March 02, 2017, 07:34:56 pm --- I'll be dimming 2 x 40w - lightbulbs (The big ballon ones with golden glow) --- End quote --- What sort of light bulbs? LED, compact fluorescent, incandescent? --- Quote from: Benta on March 02, 2017, 08:16:42 pm ---is "instructables" really like that? I've never visited them --- End quote --- Unfortunately yes. Most instructables are very poor quality. There are one or two very good ones but most are bad. There's no quality control on that site. Anyone can post crap and it doesn't get removed because it generates advertising revenue. I like to call them destructables. |
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