what is RSC 0.22 and CT 470pF

Discussion in 'Homework Help' started by bug13, Aug 2, 2012.

  1. bug13

    Thread Starter Senior Member

    Feb 13, 2012
  2. #12


    Nov 30, 2010
    Much as I suspected, Rsc is a maximum current detector (Figure 10) and Ct is "Capacitor, timing" for the oscillator (Figure 6).
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  3. WBahn


    Mar 31, 2012
    Look at the pin descriptions on Page 2.

    It specifically states:

    Pin 6: Peak Current Sense Input by monitoring the voltage drop
    across an external current sense resistor to limit the peak current
    through the switch

    Pin 3: Timing Capacitor to control the switching frequency
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  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
    34063 does not work a pure PWM controller. This circuit work more like a PFM ( pulse frequency modulation ) controller.
    How does it work? The ic contains a local oscillator and a BJT switch.
    If the comparator input (5) voltage is below the reference voltage (about 1.25V), the generator starts and turns ON the switch.
    How long the switch (BJT) is ON depends on two factors:
    1. Maximum Ton time for a given Ct
    2. Voltage drop across Rsc resistor reach 0.3V
    After meeting one of the above conditions the Switch is OFF at least for Toff time (set by Ct).
    If the voltage at comparator input (5 leg) did not reach about 1.25V - the cycle repeats.
    This is why this controller some times enter hiccup mode.
    More on how 34063 work here
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