Other Parts Discussed in Thread: MC33063A, ALLIGATOR
I'm using an external P-chan FET for higher supply current. I worked through the formulas to determine my minimum inductance and output capacitance needed for my application. What should I be seeing for the current going through the inductor.
The datasheet shows a consistent sawtooth starting at 0A and rising to about double my required DC current requirement. My circuit actually shows the the sawtooth bouncing around and teeth beginning in the middle of another teeth. Some teeth don't start or drop to 0A. I'm driving a brushless DC fan (~1.6A running) and am thinking my layout (circuit ground and current paths may not be adequately controlled) and the fan noise may be coupling into the MC33063.
What should the inductor current look like in a properly working switcher? Should the sawtooth always start a 0A and end at 0A? Will there be gaps between teeth? Should the peak amplitude of all the teeth be consistent? This is a PWM controller. The inductor waveform frequency should be consistent (set by Ct), and the output voltage is controlled by on/off time? Is that correct? The Oscope waveform below is a result of placing a 0.01uF cap across the lower feedback resistor, otherwise the waveform looks way worse.
Thx in advance!