How does the current limiting work in the MC33063. The datasheet doesn't explain the actual mechanism.
"Michael Robinson"
** OnSemi do have "app notes" you know !!See page 3 of the pdf, just under figure 4.
Seems the current sense circuit ( Ipk Sense) INCREASES the current going to Ct and hence makes the output stage on time less. So the second of your hunches applies.
..... Phil
n't
34063A-D.PDF aIt truncates the duty cycle when the INPUT current reaches the trip point; the output current is apparently not sensed directly. It's only a limit on the peak value of the input current, not an average, but of course that value and the operating frequency sets a current output limit.
"Michael Robinson" kirjoitti viestissä:w3S0n.1953$ snipped-for-privacy@newsfe18.iad...
It charges timing capacitor to some high voltage if input current exceeds threshold => Output disabled until discharged back to normal current.
-ek
The other posters have expalined how it works.
The current limit is poorly defined. It can not be used to provide a constant current supply. If you need that then you need extra components.
You could use the NCP3063 or MC34063 as a constant current driver but why would you? You could program the output current by Iout = Vref/Rout. But you're much better off using a constant current controller with a much lower reference like the TPS40211 or Onsemis NCP3065.
This application note describes an elaborate CC driver using the NCP3063
350 mA CC DriverFor comparison here is the NCP3065 constant current controller. This controller is almost identical to the 3063 hysteretic control etc but with a 235mV reference.
It has already been explained how the current limit works but here is a more detailed application note. See page 3.
How not to build a constant current driver with the NCP3063.
My guess it would have to be duty cycle..
Current limiting takes precedence with the value of Rsc, (6) and (7) obviously are some internal comparator that will gate the duty cycle shorter when needed.
If this isn't enough to maintain V, the comp for V just simply attempts a max duty cycle, which will only be what the current limiting circuit allows.
Briefly looking at it, that is what I get from it..
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