MC34067, MC33067
http://onsemi.com
12
The maximum duty cycle is controlled by the leakage
inductance, not by the MC34067. The One
−
Shot in the
MC34067 only assures that the power switch is turned on
under a zero voltage condition. Adjust the one
−
shot period
so that the output switch is activated while the primary
current is slewing but before the current changes polarity.
The resonant stage should then be designed to be as long as
the time for the primary current to go to 0 A.
Figure 21. Application Timing Diagram
0 A
+ I
primary
- I
primary
Output Rectifier Voltage
0 V
1/2 V
in
V
in
Drive Output B
Drive Output A
One-Shot
3.6 V
5.1 V
C
OSC
3.6 V
5.1 V
V
in
/Turns Ratio
Primary Current
Input Voltage
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