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BL8896
High-performance current mode PWM Controller
GENERAL DESCRIPTION
FEATURES
BL8896 is a high-performance current mode
PWM control IC designed for AC/DC convertor,
which built-in high-voltage power switch tube and
supplies continuous output power of 10W within
the range of wide-voltage between 85V and
300V, the output power of peak value can be up
to 12W.The combination of optimized reasonable
circuit design and bipolar facture technology with
high performance and price ratio economizes the
whole cost ultimately. The power controller can
be applied to the typical flyback circuit topology
so as to form a simple AC/DC transformer. IC
circuit can use the power switch tube itself within
a larger version of startup, greatly reduces the
power loss of starting resistance .IC built-in PFM
function that when the output power increases
then the working frequency increases, thus
reducing switching loss and achieving high
efficiency when the power output decreases. The
PFM function combination of patent drive circuit
that can easily meet "of energy Star 2.0" strict
requirements. When VCC reaches 12V, the chip
internal over voltage protection activates and
limits the output voltage rising. That can prevent
the too high output voltage because the light
coupling or the feedback circuit damaged. The
circuit built-in the input voltage compensation
function, which realizes the constant output
power limiting in the whole power grid conditions.
In the IC internal that provides the overload and
the perfect saturation function. It can real time
control van overload, transformer saturation,
output short circuit in abnormal condition, so
improving the reliability of power supply. IC has
integrated the internal temperature protection
function, when the system is overheating, the
output power will be lower, or shuts down the
output. We can provide meeting ROHS and
green environmental protection requirements of
DIP-8 standard.
■ Meeting AC85-300V input voltage range of the
design requirements
■ Low starting current and working current
■ The standby power consumption can be
as low as 0.15W
■ Improve driving circuit efficiency 2-3%
■ Meeting the requirements of energy efficiency
energy star 2.0
■ With temperature compensation function
accurate current control
■ Wide voltage continuous output power can be
up to 10W, the peak output power can be up to
12W
■ AC line compensation
■ With functions of thermal protection (OTP)
■ With functions of over voltage protection (OVP)
■ Can be realized without Y capacitor system
design
■ Less peripheral components, and the overall
scheme of low cost
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APPLICATIONS
■ The charger
■ DVD/DVB power
■ Small appliances (such as: induction cooker)
■ PC&LCD TV standby power supply
■ The power adapter (such as communications
terminal products)
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BL8896
High-performance current mode PWM Controller
TYPICAL APPLICATION
Figure 1 Typical application diagram
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BL8896
High-performance current mode PWM Controller
GENERALINFORMATION
Pin Configuration
The pin map is shown as below for DIP-8
Absolute Maximum Ratings
Power supply voltage VCC
18V
Pins input voltage
VCC+0.3V
Endurance voltage of OC collector
-0.3-750V
VIN
OC
Switching current of peak value
1000mA
VCC
OC
Total dissipation power
1500mW
IS
Operating temperature range
-20 to +125℃
Deposit temperature range
-55 to +150℃
GND
BL8896
FB
NC
Welding temperature
+260℃,10S
TERMINAL ASSIGNMENTS
Pin Num.
Pin Name
I/O
Description
1
VIN
I
Circuit input compensation and high voltage current source to trigger
feet, external compensation resistance
2
VCC
P
Power Supply
3
GND
P
Ground
4
NC
5
FB
I
Feedback pins
6
IS
I
Switching current sampling and limit enactment, sampling resistance
of external current
7/8
OC
O
Output pins, meet switching transformer
No Connection
Recommended operating conditions
PARAMETER
MIN
Power supply voltage VCC
5
Pins input voltage
-0.3
Peak inverse voltage
-
Switching current of peak value
Operating temperature
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TYP
MAX
UNIT
10
V
-
Vcc
V
-
650
V
-
800
-10
100
mA
℃
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BL8896
High-performance current mode PWM Controller
BLOCK DIAGRAM
Figure 2 schematic diagram
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BL8896
High-performance current mode PWM Controller
ELECTRICAL CHARACTERISTICS
(Ta=25℃, VCC=5.5-7.5V, RS=1Ω, if not otherwise noted)
Parameter
Symbol
Test Conditions
Min
I_OC=10mA
750
Typ
Max
Unit
Output Section
Max withstanding voltage of the
switching tube
Saturation voltage
Output Rise time
Output Fall time
Vsat
TR
TF
V
I_OC=500mA
CL=1nF
CL=1nF
0.8
75
75
V
ns
ns
Current Sampling Section
Current sampling threshold
The maximum current
Transmission delay
Oscillator Section
Oscillating Frequency
Voltage stability
Temperature stability
RS=1Ω
0.63
0.65
V
0.61
-
0.63
150
0.65
250
A
ns
KHz
%
%
ns
F_OSC
65
VCC=5-10V
Ta=0-85℃
Leading edge blanking time
Feedback Section
FB Input
impedance
0.61
Pull up Current
Pull down Resistor
-
500
1
1
-
-
550
40
-
uA
KΩ
55
-
60
1.5
65
-
%
%
15
2.0
1.0
8.9
2.5
12
50
-
uA
mA
mA
V
V
V
PWM Section
Maximum Duty Ratio
Minimum Duty Ratio
D_max
D_min
VFB=2.5V
VFB=0V
Power Supply Current Section
Initiation Static Current
Static Current
High voltage current source
IQ
VCC=8.0V
Startup voltage
Oscillator turn off voltage
Over Voltage limiting Threshold
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-
Vac>80V
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5
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BL8896
High-performance current mode PWM Controller
OPERATION DESCRIPTION
●Start control: During start-up phase, the internal
●Standby
benchmark,
and
In standby mode, when the output voltage
protection circuit is stopped working, the small
increases, then the FB voltages lower. If the FB
current of 50uA on the starting resistance is input
voltage is less than 1.8V (about between
from VIN to the base of the Power Transistor, the
1.2-1.8V) then the oscillator cycle will increase,
amplifying current from Emitter through current
the smaller FB, the wider oscillator cycle. This
oscillators,
driving
circuit
limiting circuit outflows to VCC, more than 50uA feature
frequency reduction control circuit:
is
to
reduce
the
standby
power
current part charge to parallel capacitor of VCC,
consumption and prevent the occurrence of audio
when VCC voltage rises to 8.9 V, entering a state
interference at the same time.
of PWM control chip.
●Efficient
●PWM
makes the switch tube in critical saturation driving
control: The voltage of FB pins through the
driving circuit: The efficient driving circuit
partial pressure resistance exports to the PWM
state, improving the frequency of the triode,
comparator as the peak switching current
effectively
reference, the FB signal determines the size of the
improving the work efficiency of the whole system,
switch tube peak current, through the FB to realize
greatly reducing the fever of the chip at the same
the control of the PWM control. At the same time
time. That makes the system more reliable.
the Output pulse duty ratio is limited by maximum
●AC
duty cycle, the FB is controlled by internal and
the voltage size and real-time compensate the
external feedback circuit.
maximum output power; this makes the maximum
●External
limiting power constant. When high and low ac is
feedback circuit: After amplification the
reducing
the
triode
switch
loss,
line compensation: The chip from VIN detects
system output error adjusting signal is converted
input.
into current signal that can adjust the voltage of FB
●Thermal
by isolation transmission of the optocoupler. The
temperature is higher than 140℃, then making the
heavier load, the smaller optocoupler current, the
internal FB voltage reducing and the oscillator
higher FB voltage, the greater duty ratio of PWM
cycle widening, reducing or closing the power
signal, the output power increases, and vice versa,
output, so the BL8896 temperature does not
the load is light, the feedback current is added, the
exceed 150℃ in order to achieve protection.
protection function: When the internal
FB voltage decreases, the duty ratio decreases,
and the output decreases, so as to realize the
adjustment of the output voltage.
●VCC
overvoltage
protection
circuit:
if
the
peripheral feedback makes the VCC increasing
that is more than 12V, then the internal feedback
circuit makes the FB voltage reducing and
reducing the output power, it makes the VCC
voltage keeping in 12V, this feature can prevent the
output voltage increasing because the optocoupler
or feedback is damaged. Thus the secondary
circuit and its output load will not damage.
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BL8896
High-performance current mode PWM Controller
Electric Parameter Definitions
Application information
●Start-up
static current: The minimum current
sourcing current which can enable VCC
surging when VCC is connected to a filter
capacitor and an adjustable current sourcing.
●Start-up voltage: The maximum of VCC
above.
●Restart-up voltage: The minimum of VCC
above.
●Oscillator shut-down voltage: The Negative
edge of VCC above; the value of VCC which
can stop the oscillator.
●Static current: The VCC power supply current
in normal period when FB is connected to the
ground by a 1.0KΩ resistance.
●FB pull up current: which occurs in normal
period, when FB=2.5V, and IS=0A.
●FB upper current protection: The pull down
current of FB when FB=2.0V and IS=0.3A in
normal period.
● FB
feedback and control
In normal working state, the FB voltage will
determine the maximum switching current value,
the higher the voltage, the bigger switch current
(only limited to peak current limit). The FB pin
internal pull-up 550uA current source, pull-down
about 40KΩ resistor (approximate equivalent), An
external resistor reduces the depth of the
feedback, the size of the external resistance will
not affect the maximum peak current, it is
recommended to use 7.5K to 10K resistor, an
external resistor can improve reaction speed of the
system with overload and the input voltage
jumping. It is advantageous to the short circuit
protection. Moreover the FB voltage below 1.8V,
will make the period of oscillation widening, the
switch frequency falling, It is lower than 1.8V, the
frequency will be lower. FB converter capacitance
will affect feedback bandwidth, thus influence
some external parameters, such as transient
characteristics.
●The
VCC voltage limit: The value of VCC when
there is no feedback circuit of BL8896 in
normal period.
●OC upper limit current: If FB=2.0V, the
minimum OC current when there is pull down
current in FB.
Figure 3. FB feedback and control
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V1.0
BL8896
High-performance current mode PWM Controller
Typical applications for CFB capacitance value,
can be between 10-100nF selection based on the
frequency characteristics of the feedback loop,
General application can use the 100nF.
● Over temperature protection
IC has built-in precision over temperature
protection function. In the chip internal when the
temperature reaches 140 ℃ , the thermal
protection circuit pulls down the clock signal, and
the switch frequency is reduced in order to reduce
the power consumption. The Switching frequency
decreases with the rise of the temperature, and
until the oscillation shuts down. As shown in the
figure below
Figure 4.Over temperature protection
●Power tube driving characteristics and
high pressure offset technology
In the IC internal, it has an unique offset
technology, at the time of power tube shutting off,
the base output of Power Transistor drops down to
the ground instantly, at the same time the offset
output voltage of emitter is greater than the base.
Launching E junction reverse, it accelerates the IC
current rate of descent and expands the effective
security work area, The CB of the switch tube is in
the reverse voltage that achieves greater than
750V voltage. About more details of the switch
tube please refer to the relevant technical data
compression characteristics.
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Figure5 The collector emitter clamping voltage
Offset waveform as shown in the figure below:
Figure 6 Vbe driving voltage waveform
●Over voltage and under-voltage protection
IC has with hysteresis under voltage protection
function. When the VCC voltage achieves to 8.9 V
the IC will start, the initial voltage is provided by a
driving resistor, the input of high voltage through
the driving resistor enters to B injection of the
switch tube, the amplifying IC current through
current limiting circuit outflows to VCC capacitor
Thus forming the driving voltage. The VCC voltage
should be maintained in between 5-10V (including
full load) in the normal working, if the VCC voltage
pulls down to 2.5V the oscillator will enter closed
state.
V1.0
BL8896
High-performance current mode PWM Controller
In IC internal, the VCC has an upper limit voltage
comparator control, if the VCC is more than 12V
the comparator actions, the FB will be drop-down,
locking the VCC in 12V, achieving over-voltage
limit function. Use this function, it can easily
achieve front end voltage feedback function; also
can avoid the output voltage rising significantly in
the open loop, guaranteeing the safety of the load.
Therefore, the VCC should keep in a suitable
range and avoid the VCC rising too high with large
output loads, leading to the output voltage
dropping because the IC overvoltage limitation.
●Coil larges current programming and
driving current compensation circuit
Figure 7 Coil larges current programming
and driving current compensation circuit
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The IC has a current limiting function. Each
switching cycle detects the switching current, when
it achieves the setting current of the FB or the
upper limit of the current, then entering the closed
cycle, the current detection has the functions of
real-time leading edge blanking, shielding
switching peak, avoiding error detection of the
switching current. The reasonable temperature
compensation eliminates the influence of the
temperature, relative to conventional transistor, the
switching current in a wide range can be very
accurate, this don't have too big margin when
designing scheme, then can satisfy work in big
temperature range, improving the use safety of the
circuit.
Inside the IS chip connects a resistor R1 to the
ground, using to compensate the influence of the
internal drive current to the coil current. Its
corresponding relationship is I drive*R1=0.7V, the
biggest coil current is calculated according to the
volume of power, this can be made of the external
resistance R2 programming, its relationship is:
Iwinding(Max)=0.7/R2. As a result of the existence of
the internal resistor R1. When calculating the R2
value will not consider the influence of the internal
drive current to the coil current.
V1.0
BL8896
High-performance current mode PWM Controller
● The
heat dissipation requirements
● VCC
design points
As a result of the drive technology breakthrough,
When the VCC voltage rises to 8.9V, the IC will
the chip internal loss (fever) 40% less than the PIN
start, the VCC capacitor will store enough power
TO PIN the other products, but for a typical power
for IC before entering normal working until
switch,
cooling
establishing normal output voltage; So the VCC
measures, in order to avoid high temperature lead
capacitor is not too small, and the reasonable VCC
to thermal protection. In the IC internal, this main
capacitor is 22uF.
should
use
the
necessary
heating is the generated by the switching loss, so
the appropriate cooling position is the IC Pin7-8
feet, an easy to use method is laid a certain area
of PCB copper foil in Pin7-8 feet, especially it will
increase thermal capacity on copper foil tinning,
For a 85-265V input, typical application of 10W
output, 200mm ² is the size of copper foil is
necessary.
Figure 8 Heat dissipation map
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BL8896
High-performance current mode PWM Controller
Package size
Symbol
Dimensions In Inches
Min
Max
Min
Max
A
3.710
4.310
0.146
0.170
A1
0.510
0.020
-
A2
3.200
3.600
0.126
0.142
B
0.380
0.570
0.015
0.020
B1
1.524(BSC)
0.060(BSC)
C
0.204
0.360
0.008
0.014
D
9.000
9.400
0.354
0.370
E
6.200
6.600
0.244
0.260
E1
7.320
7.920
0.288
0.312
e
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Dimensions In
Millimeters
2.540(BSC)
0.100(BSC)
L
3.00
3.60
0.118
0.142
E2
8.400
9.000
0.331
0.354
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BL8896
High-performance current mode PWM Controller
IC reference junction temperature and thermal resistance
IC reference junction temperature and thermal resistance
DIP8 encapsulating junction temperature data
(θJC)1 …………………………………………………………………25℃/W
(θJA)2 …………………………………………………………………70℃/W
Note: 1. The test points to Pin7, 8 close to encapsulate the position.
2. Pin7, 8 are connected in a 2 oz copper area of not less than 200mm².
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