MC34063A chip advice

Discussion in 'The Projects Forum' started by airplane100000, Oct 1, 2016.

  1. airplane100000

    Thread Starter Member

    Aug 2, 2016
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    0
    I am designing a primitive flyback converter with no feedback. I was considering to accomplish the switching by means of a PIC and a MOSFET.
    I then stumbled along this chip: MC34063A , which (correct me if I'm mistaken) does the same thing. It is programmed with this tool.
    Is it correct to say that for a given frequency and duty cycle, it outputs the given voltage and current, then opens the "switch"?
    If so it seems to meet the bill, the only problem is that I need a low frequency, circa 100hz. According to the spec its min. frequency is 24khz.
    I then stumbled along this "variant", which claims to have a min. of 100hz: KA34063A.

    Does this solve my problem? If not, is there a better way to do this (looking for low cost and simplicity)
    Any response is appreciated
     
    Last edited: Oct 1, 2016
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,658
    632
    It may not completely solve your problem but it is a great start (you still need to find the other parts!).

    I have used the KA34063 and the tool to which you linked for both flyback and boost converters and experienced no problems.

    Cosider the preceeding to be an endorsement.
     
  3. airplane100000

    Thread Starter Member

    Aug 2, 2016
    59
    0
    Wait but I was just thinking, this chip actually can't be used to charge the primary of the transformer right? Being that it is a voltage regulator, its output voltage will always be what it is programmed to be, and will therefor not fall below that value. It cannot replace the MOSFET, only drive the MOSFET.

    Is that correct to say?
     
  4. DickCappels

    Moderator

    Aug 21, 2008
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    The circuit below is from the Motorola application note. Notice that the feedback is taken from the output. (A transformer or an simple inductor may be used.) The output voltage of the circuit will be that which it is set by the resistors connected to pin 5. The timing of the primary on the drive is automatically adjusted to maintain that voltage.

    upload_2016-10-3_10-39-44.png
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    First of all at 100 Hz there is not much energy transfered. If you had a large enough inductor, yes, but typically its in the 100uH range.

    This IC has a small transistor built in which is good for small currents. But youd see it turns hot easily because its not a very efficient IC. Good for 100mA or so.

    With a MOSFET and suitable parts you can get better efficiency.
     
  6. DickCappels

    Moderator

    Aug 21, 2008
    2,658
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    Would you please why you want to do this at 100 Hz?
     
    JWHassler likes this.
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