mc33063 current limiting
in [Design]
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From: Michael Robinson on 5 Jan 2010 20:54 How does the current limiting work in the MC33063. The datasheet doesn't explain the actual mechanism. http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF Does it discharge the timing cap when it detects overcurrent, which would restart the oscillator, or does it let the oscillator keep running but at a lower duty cycle?
From: whit3rd on 6 Jan 2010 01:56 On Jan 5, 5:54 pm, "Michael Robinson" <nos...(a)billburg.com> wrote: > How does the current limiting work in the MC33063. The datasheet doesn't > explain the actual mechanism.http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF > Does it discharge the timing cap when it detects overcurrent, which would > restart the oscillator, or does it let the oscillator keep running but at a > lower duty cycle? It 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.
From: E on 6 Jan 2010 03:26 "Michael Robinson" <nospam(a)billburg.com> kirjoitti viestiss�:w3S0n.1953$ap2.1686(a)newsfe18.iad... > How does the current limiting work in the MC33063. The datasheet doesn't > explain the actual mechanism. > http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF > Does it discharge the timing cap when it detects overcurrent, which would > restart the oscillator, or does it let the oscillator keep running but at > a lower duty cycle? > It charges timing capacitor to some high voltage if input current exceeds threshold => Output disabled until discharged back to normal current. -ek
From: Raveninghorde on 6 Jan 2010 05:59 On Tue, 5 Jan 2010 20:54:40 -0500, "Michael Robinson" <nospam(a)billburg.com> wrote: >How does the current limiting work in the MC33063. The datasheet doesn't >explain the actual mechanism. >http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF >Does it discharge the timing cap when it detects overcurrent, which would >restart the oscillator, or does it let the oscillator keep running but at a >lower duty cycle? > 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.
From: Hammy on 6 Jan 2010 06:39
On Tue, 5 Jan 2010 20:54:40 -0500, "Michael Robinson" <nospam(a)billburg.com> wrote: >How does the current limiting work in the MC33063. The datasheet doesn't >explain the actual mechanism. >http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF >Does it discharge the timing cap when it detects overcurrent, which would >restart the oscillator, or does it let the oscillator keep running but at a >lower duty cycle? > 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 Driver http://www.eetasia.com/ARTICLES/2008JAN/PDF/EEOL_2008JAN31_OPT_CTRLD_AN.pdf?SOURCES=DOWNLOAD 700 mA CC driver http://www.eetindia.co.in/STATIC/PDF/200809/EEIOL_2008SEP12_OPTO_AN_01.pdf?SOURCES=DOWNLOAD For comparison here is the NCP3065 constant current controller. This controller is almost identical to the 3063 hysteretic control etc but with a 235mV reference. http://www.onsemi.com/pub/Collateral/NCP3065.PDF It has already been explained how the current limit works but here is a more detailed application note. See page 3. http://www.intusoft.com/onsemipdfs/AN920-D.pdf |