KSQ mit LM317???

  • Thanks for your answer. But i dont understand why do you have +12V?? The Transistor who is not named is the logic level mosfet or??? ULED is the voltage what all LEDs need, is that right? For what is the Pin PWM? Also i mean what function has it? For what maximal power is this shematic?

  • 1.
    +12 V is used to provide full opening of ANY (N channel of course) mosfet You use, so there is no need to use logic level mosfets. You can use also smaller voltage, but I have used +12V because it it very common and works well with ANY mosfet.


    2.
    Yes, Uled is the voltage which can be measured on the led string when full (rated) current flows through... (This should be measured in cold conditions at the start - the leds should not be warm like after some operation)


    3.
    The PWM pin is the input where You should connect Your uC PWM output signal. When positive voltage is at the uC output (on state), the mosfet opens and feeds the right current into the leds. After the positive voltage is shut down the mosfet closes. And this is happening cycle by cycle according to Your PWM signal from uC. This applies to the modified schematic of course, the first schematic is activated by switching to ground at input. After look into datasheet for Your uC either should be possible.


    4.
    There are no power limitations for this schematic, everything depends on the mosfet power, current and voltage capability, the resistor(s) connected to mosfet drain must have also enough power according to the current which flows through it. I wrote the equations before...
    So You can easily use string of 30pcs 3W leds (30x3,5V=105V - take 200V mosfet, measure led string voltage when operating at full current and calculate desirable supply voltage) or divide the string to 3x10 and use triple schematic with 100V mosfets etc...


    I think You should buy som cheap mosfet and the few other components and try it out with some leds and suitable supply! Costs about 1EUR all, but gives You RICH experience...
    For example take 3 leds, 12V supply for both leds and electronics, and some IRFZ44 or similar...
    For 350mA use 0,65/0,35=1,8 Ohm resistor (small 0,6W one will be enough)
    For 700mA use 0,65/0,7=0,9 Ohm resistor (1,5 Ohm and 2,2 Ohm in parallel, 0,6W each)


    I'm waiting for Your experience... And for first try use some car bulb in the place for leds to avoid burning them if something goes wrong... You can adjust the exact current by adjusting the resistor value.


    Good luck!