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PDF LD7912J Data sheet ( Hoja de datos )
| Número de pieza | LD7912J | |
| Descripción | Green Mode Power Switch | |
| Fabricantes | Leadtrend Technology | |
| Logotipo |  |
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LD7912J
9/5/2012
Green Mode Power Switch with BNO
REV：00
General Description
The LD7912J is a green mode PWM controller integrated
with a 700V MOSFET in a DIP-7 package. It’s capable to
operate at fixed frequency of 100KHz. With multi-functions
built in this device , such as high voltage startup, Burn-in/out
/OLP/OVP/OTP protection, internal current mode slope
compensation, and green-mode power-saving operation
under light load or no load condition, this highly integrated
device provides high efficiency, low external component
counts, and low cost solution for compact power
applications.
Features
Built-in 700V Power MOSFET
Built-in High Voltage startup circuit
Fixed Switching Frequency at 100KHz
Frequency Swapping for EMI improve
Internal High Voltage Startup Circuit
Under Voltage Lockout (UVLO) on VCC Pin
Current Mode Control with Slope Compensation
Green-Mode Control for Power Saving
OVP / OLP / Internal Thermal Shut Down
Applications
Switching AC/DC Adaptor
LCD TV or PC Standby Power
SMPS for LCD Monitor
Typical Application
EMI
Filter
~
+
~
VCC Drain
LD7912J
BNO
COMP GND
S
Leadtrend Technology Corporation
LD7912J-DS-00 September 2012
1
www.leadtrend.com.tw
1 page  
LD7912J
Absolute Maximum Ratings
Supply Voltage VCC
COMP, BNO
S pin DC Voltage
S pin negative pulse voltage (Duration Time < 100nS)
Drain
Peak Pulse drain current
Total Maximum Power Dissipation of (25°C)
Package thermal resistance (DIP-7)
θJA
θJC
Operating Junction Temperature Range
Operating Ambient Temperature Range
Storage Temperature Range
Lead temperature (Soldering, 10sec)
ESD Voltage Protection, Human Body Model (Exclusive Drain Pin)
ESD Voltage Protection, Machine Model (Exclusive Drain Pin)
-0.3V~30V
-0.3V ~7V
-0.3V ~7V
-1.5V
-0.3V~700V
2A
1.25W
80°C/W
35°C/W
-40°C to 125°C
-40°C to 85°C
-65°C to 150°C
260°C
2.5KV
250 V
Caution:
Stresses beyond the ratings specified in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only
rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not
implied.
Leadtrend Technology Corporation
LD7912J-DS-00 September 2012
5
www.leadtrend.com.tw
5 Page 
LD7912J
Current Sensing and Leading-edge Blanking
Through current and voltage signal delivered from the
typical current mode of PWM controller, it is able to close
the control loop and achieve regulation. The LD7912J
detects the internal MOSFET current from S pin and
pulse-by-pulse limit current. The maximum voltage
threshold of the current sensing pin is Vcs_off (~0.45V). The
MOSFET peak current can be obtained from below
equation.
IPEAK(MAX )
Vcs _ of f
RS
Due to the integrated leading edge blanking circuit and
internal spike filter, it is free from external LC filter parts.
Internal Slope Compensation
Stability is crucial for current mode control when it operates
at CCM and more than 50% of duty-cycle. To stabilize the
control loop, the slope compensation is required in the
traditional UC384X design by injecting the ramp signal from
the RT/CT pin through a coupling capacitor. With this
function built in, the LD7912J is ideal to optimize the
external circuit design.
On/Off Control
The gate driver of LD7912J can be disabled immediately by
pulling COMP pin voltage level below Zero Duty Trip Level.
The disable-mode will be released once COMP pin voltage
level ramps higher above Zero Duty Trip Level.
Oscillator and Switching Frequency
The switching frequency of LD7912J is fixed at 100KHz to
provide the optimized operations in the good conditions of
EMI performance, thermal treatment, component sizes and
transformer design. The swapping frequency is internally set
between 6.2KHz to incorporate with 100KHz switching
frequency.
Green-Mode Operation
In using the green-mode control, the switching frequency
can be reduced under the light load condition. This feature
helps to enhance the efficiency in light load conditions. The
green-mode control is Leadtrend Technology’s own IP.
Maximum Duty-Cycle
The maximum duty-cycle of LD7912J is limited to 75% to
avoid the transformer saturation.
Voltage Feedback Loop
The voltage feedback signal is provided from the TL431 in
the secondary side through the photo-coupler to the COMP
pin of LD7912J. The input stage of LD7912J, as UC384X,
is incorporated with 2 diodes voltage offset circuit and a
voltage divider with 1/6 ratio. Therefore,
V(PWMCOMPARATOR )
1
6
(VCOMP
2VF )
A pull-high resistor is embedded internally to eliminate an
external one.
OVP (Over Voltage Protection) on Vcc
LD7912J is implemented with OVP function on Vcc. As
Vcc voltage rises above OVP threshold voltage, the output
gate drive circuit will be shutdown and stop the switching of
the power MOSFET.
If the fault condition is removed, the LD 7912J will automatic
restart at the next UVLO(on).
If the fault condition is not removed till next UVLO(on), the
Vcc will trip to OVP level and shutdown the output again.
Leadtrend Technology Corporation
LD7912J-DS-00 September 2012
11
www.leadtrend.com.tw
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LD7912J.PDF ] | |
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