SSC2005SC Просмотр технического описания (PDF) - Sanken Electric co.,ltd.
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SSC2005SC Datasheet PDF : 19 Pages
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SSC2005SC
8. Operational Description
All of the parameter values used in these descriptions
are typical values, unless they are specified as
minimum or maximum.
With regard to current direction, "+" indicates sink
current (toward the IC) and "–" indicates source
current (from the IC).
8.1 Critical Conduction Mode: CRM
Figure 8-1 and Figure 8-2 show the PFC circuit and
CRM operation waveform. The IC performs the on/off
operation of switching device Q1 in critical mode (the
inductor current is zero) as shown in Figure 8-1. Thus,
the low drain current variation di/dt of power MOSFET
is accomplished. Also, adjusting the turn-on timing at
the bottom point of VDS free oscillation waveform
(quasi-resonant operation), low noise and high
efficiency PFC circuit is realized.
L1
D1
VAC
C1
Q1
IOFF
D
C2
ION
S
RCS
Figure 8-1 PFC circuit
voltage RVS2 is compared with the reference voltage
VFB = 2.50 V by using error amplifier (Error AMP)
connected to FB pin. The output of the Error AMP is
averaged and phase compensated. This signal VCOMP is
compared with the ramp signal VOSC to achieve on-time
control. The ON time becomes almost constant in
commercial cycle by setting VCOMP respond to below
20 Hz (Figure 8-4). This is achieved by tuning the
capacitor connected to the COMP pin.
The off-time and the bottom on timing of VDS are set
by both zero current detection of drain current and the
delay time configured by RDLY pin resistance. Thus,
simple PFC circuit with inductor having no auxiliary
winding is realized.
L1
D1
VOUT
Q1
RCS
U1
7
OUT
QR
S
ZCD COMP
VCS(ZCD)= -10mV
Error AMP
PWM COMP
VCOMP
FB 1
VSET
VOSC
VFB
= 2.5V
C6
OSC
CS
RT
RDLY
GND COMP
5
3
4
6
2
RS
C5 DZCS RRT C3 RDLY C4
CP
CS
RVS1
RVS2
R4
Figure 8-3 CRM control circuit
IL=ION+IOFF
I L(AVG )
1 ILPEAK
2
ION
ILPEAK
VAC(t)
IL(t)
IAC(t)
√2×VACRMS
ILPEAK
√2×IACRMS
IOFF
Bottom on
Free oscillation
Q1 VDS
OFF
ON
OFF
ON
Turn on delay time
Figure 8-2 CRM operation and bottom on operation
Figure 8-3 shows the internal CRM control circuit.
The power MOSFET Q1 starts switching operation by
self-oscillation.
The control of on-time is as follows: the detection
VCOMP
VOSC
VSET
OUT pin voltage
VAC(t)
tON tOFF
ILPEAK(t)
IL(AVG.)(t)
Figure 8-4 CRM operation waveforms
SSC2005SC-DS Rev.1.1
SANKEN ELECTRIC CO.,LTD.
8
Feb. 06, 2015
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