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Номер произв STR-W6756
Описание (STR-W6700 Series) Quasi-Resonant Switching Regulators
Производители Sanken
логотип Sanken логотип 



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STR-W6756 Даташит, Описание, Даташиты
Product Information
STR-W6700 Series Off-Line
Quasi-Resonant Switching Regulators
Introduction
The Series STR-W6750 devices are hybrid integrated cir-
cuits (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 efficiency 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 down-
sizingand standardizing of an SMPS by reducing external
componentcount and simplifying circuit design.
Features and benefits include the following:
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.
Figure 1. STR-W6700 series packages are fully molded TO-220
package types. Pin 2 is deleted for greater isolation.
Table 1. Product Line-up
Type #
STR-W6735
MOSFET
VDSS
(V)
500
RDS(on)
(Max)
(Ω)
0.57
VAC
Input
(V)
120
POUT*
(W)
160
STR-W6753
Wide
1.70
230
58
120
STR-W6754
650
Wide
0.96
230
100
160
STR-W6756
Wide
0.73
230
140
240
STR-W6765
800
Wide
1.80
230
50
110
*The listed output power represents thermal ratings, and the peak
output power, POUT , is obtained by 120% to 140% of the thermal
rating value. In case of low output voltage and narrow on-duty
cycle, the POUT (W) becomes lower than the above.
Contents
Introduction
Pin functional descriptions
Operation description
Transformer parameters
General considerations
Design considerations
Package Dimensions, TO-220
Worldwide Contacts
28103.30
1
2
6
10 All performance characteristics given are typical values for
11 circuit or system baseline design only and are at the nominal
13 operating voltage and an ambient temperature of 25°C, un-
14 less otherwise stated.
17
SANKEN ELECTRIC CO., LTD.
http://www.sanken-ele.co.jp/en/
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STR-W6756 Даташит, Описание, Даташиты
Pin functional descriptions
VCC Supply (pin 4)
Start-up circuit The start-up circuit detects the VCC pin volt-
age, 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 2. 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.
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 voltage. The VCC pin voltage falls immediately after
the control circuit starts its operation. The voltage drop can be
reduced by increasing C3 capacitance. However, too large a
C3 capacitance will cause an improperly long time to reach the
Operation-Start voltage after the initial power turn on.
In general, SMPS performs its start-up operation properly
with a value of C3 between 4.7 and 47 μF, and R2 between
47 and 150 kΩ for 120 V narrow or universal AC input, and
82 to 330 kΩ for 200 V narrow AC input.
As shown in figure 3, the circuit current is limited to 100 μA max
(VCC = 15 V, and resistor R2 with appropriate high resistance
value for the circuit) until the control circuit starts its operation.
Once the VCC pin voltage reaches 18.2 V, the control circuit
starts its operation by the start-up circuit, and supply current is
increased. Once the VCC pin voltage drops down to lower than
the Operation-Stop voltage 9.7 V, the UVLO circuit operates to
stop the control circuit, and the IC returns to its initial state.
Bias/drive winding After the control circuit starts its operation,
the power supply is operated by rectifying and smoothing the
voltage of the bias winding. Figure 4 shows the start-up voltage
waveform of the VCC pin. The bias winding voltage does not
immediately increase up to the set voltage after the control circuit
starts its operation. That is why the VCC pin voltage starts drop-
ping. The Operation-Stop voltage is set as low as 10.6 V (max),
the bias winding voltage reaches a stabilized voltage before it
drops to the Operation-Stop voltage, and the control circuit conti-
ues its operation. The bias winding voltage, in normal power sup-
ply operation, is set for the voltage across C3 to be higher than
the Operation-Stop voltage, VCC(OFF) , 10.6 V (max.) and lower
than the OVP-operation voltage, VCC(OVP) , 25.5 V (min.).
I CC
100 μ A
( MAX)
9.7 V
( TYP)
VC C
15V 18. 2 V
( TYP)
Figure 3. VCC pin current versus voltage
R2
1
D
VCC 4
STR-W6700
S/GND 3
C3
P
D2
D
Figure 2. External start-up circuit.
VCC
18.2 V
( TYP)
Operation Start
Bias Winding Voltage
10.6V
(MAX)
AC on
Start-up
failure
time
Figure 4. VCC pin voltage after start-up, capacitor C3 installed
STRY6700-AN Rev. 2.0
SANKEN ELECTRIC CO., LTD.
2
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STR-W6756 Даташит, Описание, Даташиты
In an actual power supply circuit, the VCC pin voltage might
be changed by the value of secondary output current as shown
in figure 5. C3 is fully charged by the surge voltage generated
instantly after the MOSFET turns off. In order to prevent this, it
is effective to add a resistor (R7) of several ohms to tens of ohms
in series with the diode as shown in figure 5. The optimum value
of the additional resistor is determined in accordance with the
specifications of the transformer because the VCC pin voltage is
determined by construction of the transformer.
Furthermore, the variation ratio of the VCC pin voltage becomes
worse due to a loose coupling between primary and secondary
windings of the transformer (the coupling between the bias wind-
ing and the stabilized output winding for the constant voltage
control). Therefore, when designing a transformer, the winding
position of the bias winding needs to be studied carefully.
Overvoltage protection (OVP) circuit If VCC, referencing
the S/GND pin, exceeds 27.7 V, the OVP circuit of the control
IC starts its operation and the fault mode is latched by the latch
circuit, the control IC stopping its oscillation. Generally, the VCC
pin voltage is supplied from the bias winding of the transformer,
VCC
Without R7
and the voltage is in proportion to the output voltage; thus, the
OVP circuit also operates in the case of overvoltage output of the
secondary side, for example, when the voltage detection circuit
is open. The secondary output voltage for the OVP operation
(VO(OVP)) is obtained from the following formula:
VO(OVP)
=
VO(normal operation)
VCC(normal operation)
27.7 V
(1)
Latch circuit OVP and OLP fault modes latch the oscillation
output low, which stops the power supply circuit operation. The
holding current of the latch circuit is 140 μA (max., TA = 25°C)
when the VCC pin voltage is at the Operation-Stop voltage minus
0.3 V.
In order to prevent malfunction caused by, for instance, noise,
a delay time is programmed into a timer circuit, which prevents
latch circuit operation until the OVP or OLP circuit keeps operat-
ing for more than a programmed time. During the latched mode,
the internal regulator circuit keeps running, the circuit current is
maintained at a high level, and the VCC pin voltage drops.
When the VCC pin voltage drops down to the Operation-Stop
voltage (9.7 V (typ.) ), the voltage starts rising again as the circuit
current becomes less than 140 μA. When the VCC pin voltage
reaches the Operation-Start voltage (18.2 V (typ.) ), the circuit
current increases, and the voltage drops again. Consequently,
the VCC pin voltage is maintained between 9.7 V and 18.2 V in
the latched mode. Figure 7 shows the voltage waveform in the
latched mode. The latched mode is released by decreasing the
VCC pin voltage to below 7.2 V, or in general, by shutting off the
AC input.
With R7
SS/OLP (Pin 5)
Through the SS/OLP pin, soft-start and overload protection is
enabled by connecting a 0.47 to 3.3 μF capacitor to the pin.
IO
Figure 5. VCC versus IO (secondary load)
VCC 4
STR-W6700
S/GND 3
D2
C3
R7
D
Figure 6. VCC versus IO (secondary load)
Figure 7. VCC during latch mode
STRY6700-AN Rev. 2.0
SANKEN ELECTRIC CO., LTD.
3
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