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  1. Replies
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    188

    Closed: Re: Hfe of NPN at extremely low base current

    Thanks, i now wonder if we can make R215 = 22K, and then surely the hfe will be enough to make the second bjt's vce <0.2v?

    It turns out we didnt need so much delay as the micro can be compus...
  2. Closed: Re: Circuit to pulse from 1v to 1.1v repeatedly.

    Thanks......it would need to be pfet, and i cant pull the gate down far enough as its only a 1.1v rail.
    (admittedly we could make a negative rail for this purpose but its extra components)
  3. Closed: Circuit to pulse from 1v to 1.1v repeatedly.

    Hi ,
    We need the “Output”of the following circuit to go from 1v to 1.1v as shown in the LTspice simulation. We are worried we may get too much VCE drop in the pnp….the datasheet does not tell the...
  4. Replies
    3
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    165

    Closed: Linear led current regulator

    Hello,
    We are seeking a linear led current regulator. We need it to be an error amplifier on a chip……..but the drive fet will be external, and the reference to the internal error amplifier will be...
  5. Replies
    7
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    188

    Closed: Re: Hfe of NPN at extremely low base current

    Thanks, without doing a new pcb, i am wondering if we can just replace R215 with 22k, to give more base current...then we can achieve the low enough vce_on of the q19?
    We didnt in the end need all...
  6. Replies
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    Closed: Re: Hand soldering a 6x6mm QFN (28pin)

    Thanks,
    Also, i sometimes wonder if , since i left 0.3mm pad extension outside of the body, then maybe we can use this soldering technique...
    https://www.youtube.com/watch?v=BvhE16vBfX4
    ...
  7. Closed: Does PIC16F18856 work if centre pad is left floating?

    Hello
    We have got a prototype PCB made up and realise we forgot to connect the centre pad of the PIC16F18856 footprint to ground.
    We are using the 6X6mm QFN type, shown on page 653 of the...
  8. Replies
    10
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    Closed: Re: Hand soldering a 6x6mm QFN (28pin)

    Yes thanks to all for pointing out that vss and centre pad should be connected...fortunately, their are ground pins on the edge so we will just use them.
    The chip will still work without the centre...
  9. Replies
    7
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    188

    Closed: Hfe of NPN at extremely low base current

    Hi,
    The attached is a delay circuit….when the PRIBIAS1 rail gets its 14V voltage, then Q20 holds Q19 off for some 40ms.
    However, the base current of Q20 can only be 50uA max.
    The Ic in Q20...
  10. Replies
    10
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    336

    Closed: Re: Hand soldering a 6x6mm QFN (28pin)

    Hi,
    Thanks, I think we will just have to end up trying to solder it without soldering the centre pad, as some of the small pads of the QFN achieve a ground connection anyway.
    The footprint pads...
  11. Replies
    10
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    336

    Closed: Hand soldering a 6x6mm QFN (28pin)

    Hi
    Do you think its possible to hand solder the 28 pin , 6x6mm QFN version of the PIC16F18856 by hand soldering. Eg…dragging solder along the pins, then mopping the excess up with braid?

    Page 654...
  12. Closed: Off the shelf inductor with 400V rating...for Offline Buckboost converter

    Hi,
    We are designing a 240VAC input , 10W Buckboost LED driver. LED bank is 30V.
    We are limited to using only offtheshelf inductors because of cost. The inductor needs to be rated to 400V due to...
  13. Closed: LNK304 input voltage below the datasheet minimum value...damage?

    Hello
    We are using the LNK304 on our PCB to supply 12V at 80mA.
    Mains is 240VAC.
    We wish to keep the input capacitance to the LNK304 at two parallel pieces of 100nF, 1812, 630V, X7R. (ie 200nF)...
  14. Replies
    29
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    1,168

    Closed: Re: Synchronous Buck Converter FET selection

    There are linear.com sync buck drivers which have bootstrap drive for a top side nfet, and these I think are better.
    You always need a series gate resistor , as EasyPeasy said, even if you end up...
  15. Closed: Inrush pulse in FET in offline SMPS....gradual degradation?

    Hello,
    We suffer the attached inrush pulse (VDS and IDS) into the FET M1, which is IPP90R1K2C3.
    LTspice sim also attached.
    (it’s the input stage to an offline smps)
    The inrush happens every time...
  16. Closed: Inrush pulse in 0R56, 1206 resistor....gradual degradation?

    Hello,

    We have a 0R56 , 1206 resistor which suffers the attached inrush power pulse at switch-ON. (shown in 2 scope shots of the same thing, but one is a close up)
    The initial high pulse, which...
  17. Replies
    1
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    236

    Closed: LTspice model for COB LED

    Hi,
    Do you know how I can get a LTspice model for the LC019D and LC033D LEDs from Samsung?
    Ie something that gives the same I,V curve when a DC sweep is done?
    (pages 26,27 of datasheet)...
  18. Closed: Re: Loading PIC micro programming pins ICSPDAT and ICSPCLK

    thanks, we are wondering if we can just get away with a 1k resistor to isolate the ICSPDAT pin from the external circuitry?...it would mean the ICSPDAT needing to be able to source some 3mA...which...
  19. Closed: Re: Translating a FET drive signal up in voltage

    pwm frequency is 500Hz. Load is just 2 little sot23 fets being driven on/off
  20. Closed: Re: Loading PIC micro programming pins ICSPDAT and ICSPCLK

    Programmer rating
  21. Closed: Re: Translating a FET drive signal up in voltage

    Thanks, yes, we will feed it a high side bias supply.
  22. Closed: Translating a FET drive signal up in voltage

    Hi
    We need to switch some PWM dimming FETs on and off. These FETs sit on top of a 100V rail and the driving micro sits at 0V…therefore we need to translate the drive signal up in voltage.
    We can...
  23. Closed: Loading PIC micro programming pins ICSPDAT and ICSPCLK

    Hi,
    We are using PIC16F1503. We need to use one of the programming pins, either ICSPDAT or ICSPCLK in the circuit to turn on a high Z input. The pickit3 programmer doesn’t tell what is the maximum...
  24. Closed: LTspice sim opf Synchronous 2 transistor forward

    Hello,
    Do you know why this LTspice simulation of a synchronous 2 transistor forward converter using LTC3705 and LTC3706 won’t even start switching the fets?
    LTspice sim and scm attached

    LTC3705...
  25. Closed: Re: Do you know what is likelihood of occurrence of tolerance extremes of L6564?

    its when its set up in fixed off time mode...
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