NCP1200AP60 ,PWM Current Mode Controller With Low Standby Power, 40/60/100kHz3AND8069/DUsing an auxiliary winding as wired according to Figure 6offers true short–circuit protec ..
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NCP1200D40R2 ,PWM Current-Mode Controller for Low-Power Universal Off-Line SuppliesON Semiconductor14, rue Paul Mesplé – BP1112 – 31035 TOULOUSE Cedex 1, FranceAPPLICATION NOTE33 (0) ..
NCP1200D40R2 ,PWM Current-Mode Controller for Low-Power Universal Off-Line SuppliesAND8076/DA 70 W Low Standby Power Supply with the NCP120x SeriesPrepared by: Christophe Basso
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NCP1200AP60-NCP1200D40R2
PWM Current-Mode Controller for Low-Power Universal Off-Line Supplies
AND8069/D
Tips and Tricks to Build
Efficient Circuits with
NCP1200
Prepared by: Christophe BassoON Semiconductor
14, rue Paul Mesplé – BP1112 – 31035 TOULOUSE Cedex 1, France
33 (0)5 34 61 11 54
e–mail: christophe.basso@
IntroductionThe NCP1200 easily lends itself to designing
Switch–Mode Power Supplies (SMPS) in a snap–shot and
its success speaks for itself. However, customers
applications (and problems) are unique and often necessitate
the addition of specific component arrangements around the
IC. As usual, solving one particular design constraint brings
another one with it, perhaps puzzling the designer even
more. This application note answers typical questions that a
designer can raise when starting his own system analysis,
but also tries to answer some problems common to
Switch–Mode Power Supply applications.
The following topics are covered in this document: Adding an External Latching Circuit for Over Voltage
Protection or Over Temperature Shutdown Driving Big Gate–charge MOSFET Reducing the Standby Power with an Auxiliary
Winding that Disables the DSS Operation Using Auxiliary Winding Without Affecting the OCP
Trip Point, but Disabling the DSS Using Auxiliary Winding Without Affecting the OCP
Trip Point and Keeping the DSS Working Inserting a Resistor with Pin 8 to Avoid
Over–dissipation of the Package ’When I Insert a Resistor in the Gate of My MOSFET,
the Supply Becomes Instable” “What MOSFET Size can I Drive in Half–wave
Configuration?” “I Have Routed my 1200 with a Large Copper Area
Around the Package. What Power can I Dissipate?” “What Power Level can I Expect from the NCP1200?” A Low–cost Open Loop Offline Converter Brown–out Protection Reducing the Burst in Overload Mode A Primary Regulated Converter for TV Sets Improving Short–circuit Protection with an Auxiliary
Adding an External Latching Circuit for Over Voltage
Protection or Over Temperature ShutdownWhen pulling NCP1200’s feedback pin below the skip
cycle level (pin1 voltage), output oscillations cease. If this
action is accomplished through a thyristor, permanent
latch–off occurs until the user cycles the VCC down and up
again by unplugging the power supply. By firing the
thyristor via a zener diode connected to an auxiliary
winding, an efficient Over Voltage Protection (OVP) circuit
can be implemented. Figure 1 depicts the solution.
At rest, when the SMPS is properly working, Q1 and Q2
are transparent to the operations because the 10 k� resistors
block them. As soon as the auxiliary winding level exceeds
the zener voltage and fires Q2, the whole SCR turns on and
via the 1N4148, pulls FB low. As a result, it immediately
stops the 1200 driving pulses: the SMPS shuts off. However,
the Dynamic Self–Supply (DSS) being still alive (VCC
ramps up and down between 10–12 V), the 47 k� resistor
keeps the SCR latched despite the disappearance of the
default. Once the user cycles VCC down and up again (e.g.
by unplugging the power supply from the mains outlet), the
SCR de–biases and allows the 1200 to restart. Q1/Q2 could
be ON Semiconductor dual combo bipolar MMBT3946DW.
If for transformer noise reasons Vpin1 is much lower than
its default value (1.4 V), a BAT54 must be wired in place of
the 1N4148 to ensure that FB passes well below Vpin1:
Q2_Vcesat + Vf < Vpin1. Increasing the value of the 47 k will
change the total latch–off behavior into auto–recovery
mode, as the default over current protection does.
A temperature shutdown can be realized on top of the
above SCR by adding a PNP, as portrayed by Figure 2. The
Negative Temperature Coefficient sensor (NTC) is selected
to pull the PNP’s base toward ground at the wanted
shutdown level. To obtain slightly more dynamic on the base
level, a simple diode is inserted in series with the emitter. A
more economic solution involves a single thermistor, also
shown on the same picture.
