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PDF ( 数据手册 , 数据表 ) W6750

零件编号 W6750
描述 STRW6750
制造商 Sanken
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W6750 数据手册, 描述, 功能
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PRODUCT
DESCRIPTION
Series STR-W6750 Off-Line
Quasi-Resonant Switching Regulators
INTRODUCTION
The Series STR-W6750 devices are hybrid integrated circuits
(HICs) with a built-in power MOSFET and a control IC
designed for quasi-resonant type switch-mode power supplies
(SMPS). In normal operation, the HIC provides high effi-
ciency and low EMI noise with bottom-skip quasi-resonant
operation during light output loads. Low power consumption
is also achieved by blocking (intermittent) oscillation during an
auto-burst mode and reduced even further in a manually
triggered (clamping an output voltage) standby mode.
The HIC is supplied in a seven-pin fully-molded TO-220-style
package with pin 2 deleted, which is suitable for downsizing
and standardizing of an SMPS by reducing external component
count and simplifying circuit design.
Features
Blocking (or intermittent) oscillation operation by reducing
output voltage in the standby mode.
In addition to the standard quasi-resonant operation, a
bottom-skip function is available for increased efficiency
from light to medium load.
Soft-start operation at start-up.
Reduced switching noise (compared to conventional PWM
hard-switching solution) with a step-drive function.
Built-in avalanche-energy-guaranteed power MOSFET (to
simplify surge-absorption circuit; no VDSS derating is
required).
Overcurrent protection (OCP), overvoltage protection
(OVP), overload protection (OLP), and maximum ON-time
control circuits are incorporated. OVP and OLP go into
a latched mode.
Able to save SMPS design time with present designs and
evaluation processes.
All performance characteristics given are typical values for
circuit or system baseline design only and, unless otherwise
stated, are at the nominal operating voltage and an ambient
temperature of +25°C, unless otherwise stated.
TERMINAL FUNCTIONS
Start-up circuit
VCC (Pin 4)
The start-up circuit detects the VCC pin voltage (pin 4), and
makes the control IC start and stop operation. The power
supply of the control IC (VCC pin input) employs a circuit as
shown in Figure 1. At start-up, C3 is charged through a start-
up resistor R2. The R2 value needs to be set for more than the
hold current of the latch circuit (140 µA max.) and to operate
at the minimum ac input.
Figure 1 – External start-up circuit
If the value of R2 is too high, the C3 charge current will be
reduced. Consequently, it will take longer to reach the
operation start-up voltage. The VCC pin voltage falls immedi-
ately after the control circuit starts its operation. The voltage
drop can be reduced by increasing C3’s capacitance. There-
fore, to maintain the start-up operation, even if the rise of the
bias winding voltage is slow, the VCC pin voltage would not
fall to the operation-stop voltage. However, too large a C3
capacitance will cause an improperly long time to reach the
operation start after the initial power turn on.
In general, SMPS performs its start-up operation properly with
a value of C3 between 4.7 µF and 47 µF, and R2 between
47 kand 150 kfor 120 V narrow or universal ac input, and
82 kto 330 kfor 200 V narrow ac input.
Sanken Power Devices
from Allegro MicroSystems







W6750 pdf, 数据表
Series STR-W6750
Off-Line Quasi-Resonant
Switching Regulators
SwRitecghuinlagtors
Quasi-resonant operation bottom-skip operation
Quasi-resonance is operated under the absolute condition of
VOCP greater than VOCPBD(BS2). When the load becomes lighter
and the drain current drops to make VOCP less than
VOCPBD(BS2), the operation is shifted to the bottom-skip mode,
and the reference voltage is automatically changed to
VOCPBD(BS1). Figure 16 shows shift timing from quasi-resonant
operation to bottom-skip operation.
Bottom-skip operation quasi-resonant operation
The bottom-skip is operated under the absolute condition of
VOCP less than VOCPBD(BS2). When the load becomes heavier
and the drain current increases to make VOCP greater than
VOCPBD(BS2), the operation is shifted to the quasi-resonant
mode, and the reference voltage is automatically changed to
VOCPBD(BS2). VOCP is the OCP/BD pin voltage at the falling
edge of the MOSFET gate voltage.
As described above, the reference voltage for bottom-skip
operation, VOCPBD(BS1) and VOCPBD(BS2), has hysteresis to make
a stable operation shift as shown in Figure 17.
Standby Operation
The Series STR-W6750 devices incorporate the burst-mode
function to reduce power consumption in the standby mode.
Two modes are available. One is auto-burst mode, and the
other (for lowest possible power dissipation) is externally
triggered burst operation.
Figure 16 – Quasi-resonant to bottom-skip operation timing
115 Northeast Cutoff, Box 15036
8 Worcester, Massachusetts 01615-0036














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