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AN667 डेटा पत्रक PDF( Datasheet डाउनलोड )


डेटा पत्रक - DESIGNING A HIGH POWER FACTOR SWITCHING PREREGULATOR WITH THE L6560/A TRANSITION MODE I.C. - ST Micro

भाग संख्या AN667
समारोह DESIGNING A HIGH POWER FACTOR SWITCHING PREREGULATOR WITH THE L6560/A TRANSITION MODE I.C.
मैन्युफैक्चरर्स ST Micro 
लोगो ST Micro लोगो 
पूर्व दर्शन
1 Page
		
<?=AN667?> डेटा पत्रक पीडीएफ

AN667 pdf
APPLICATION NOTE
The on chip features are:
Undervoltage lockout with hysteresis and
micropower start-up.
Stable error amplifier.
Output overvoltage protection.
Transition Mode Operating
Zero Current and coil Voltage detection.
Internal start oscillator.
Device Blocks Description
Supply Block (see fig. 2):
A precise bandgap reference is internally built to
ensure a good regulation.
The undervoltage comparator with hysteresis and
the very-low supply current, before the turn-on
threshold is reached, allows to minimize the start-
up and supply circuitry.
Figure 2: Supply Block Diagram
+Vi
8
REF.
H = VALID SUPPLY
-
+ L = UNDERVOLTAGE
D93IN034A
Error Amplifier and Overvoltage Detector
Block (see fig. 3):
The Error Amplifier input, through the ratio of two
external resistors connected to the output bus, al-
Figure 3: Error Amplifier and Overvoltage
Detector Block
+Vo
R1
R2
Ccomp.
1
2.5V
-
E/A
+
I
I
2
-
+
3.1V
X PWM DRIVER
D93IN035B
40µA
2/11
lows the feedback for the boosted output DC volt-
age regulation. The E/A output will be connected
to the compensation capacitor (see biasing of
I.C.) to filter the twice rectified mains frequency
(2f) so that the circuit doesn’t attempt to regulate
the output ripple.
The device is provided with an effective overvol-
tage protection (OVP), realized using the same
input pin used for the DC voltage regulation.
Since the compensation capacitor slows the E/A
response, an internal fast OVP detector is imple-
mented.
In steady state condition, the current through R1
is equal to the current in R2 because the comp.
capacitor does not allow DC current (nor of
course the inverting input of the E/A).
I
R
=
V
O
2.5
R1
V
=
2.5 V
R2
When the output voltage increase, abruptly the
current in R1 will be increased of V OUT R 1
value and since the R2 current is fixed by the in-
ternal 2.5V reference, the current must flow
through the capacitor. This current is sensed in-
side the L6560/A I.C and compared with an inter-
nal 40 µA reference. If this limit is exceeded, the
dinamic OVP is detected. As the time constant of
this fast detection is over, in case the overvoltage
condition persists (i.e. disconnected load), the
output of the E/A goes below an internal refer-
ence and the OVP condition will be confirmed.
The OVP detection disables the driver and the ex-
ternal Mosfet is forced off until the overvoltage
condition disappears. Moreover, during the OVP
conditions all the internal blocks are disabled (ex-
cept the ZCD clamp) allowing to reduce the
power consumption. The OVP limit VOUT will be
selected by the equation:
V OUT = R 1 40 µA
Zero Current Detection and Triggering Block
(see fig. 4):
Figure 4: Zero Current Detection and Triggering
Block
+Vi
5
5V
D93IN036A
+
-
1.3V
PWM
R
Q
S
DRIVER
7
GD

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