what is RSC 0.22 and CT 470pF

#12

Joined Nov 30, 2010
18,224
Much as I suspected, Rsc is a maximum current detector (Figure 10) and Ct is "Capacitor, timing" for the oscillator (Figure 6).
 

WBahn

Joined Mar 31, 2012
29,978
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
 

Jony130

Joined Feb 17, 2009
5,487
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
http://jiggerjuice.info/electronics/projects/power/mc34063.html
 
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