AN1057

```Application Note 1057
Design and Application Notes for AP3107/H System Solution
Prepared by Wang Zhao Kun
System Engineering Dept.
100mW, and the application note will show you how
to design a SMPS using AP3107/H.
1. Introduction
The AP3107/H is a high voltage start-up, current
mode
PWM
controller
with
green-mode
power-saving operation.
The AP3107/H is offered in SOIC-7 package to
realize a compact size.
The AP3107/H is specially designed for ultra low
standby power performance. Different from AP3106,
AP3107/H PWM switching frequency at normal
operation is fixed at 65kHz/130kHz internally with a
narrow range.
2. Peripheral Component
2.1 BNO Pin Resistor
The AP3107/H has the function of brown-out which
can be realized by BNO pin, the brown-out voltage is
adjusted by the resistor connected between BNO and
GND, the formula of DC input voltage and BNO pin
resistor is as the following：
Table 1. The differences Between AP3107/H and AP3106
AP3106
Frequency
Adjustable
FB Resistor
18k
Standby
Performance
Dynamic
Performace
Application
Area
AP3107/H
Fixed at
65kHz/130kHz
18k—Normal Mode
120k—Burst Mode
Better
Best
Good
A Little Bad
Adapter
LCD
Display/Standby
Power
2
VON (V ) = 0.0001(V / kΩ 2 ) × R BNO
(kΩ) − 0.1284(V / kΩ) × R BNO (kΩ) + 103.41(V )
2
VOFF (V ) = 0.0001(V / kΩ 2 ) × R BNO
(kΩ) − 0.13(V / kΩ) × R BNO (kΩ) + 96.181(V )
Where：
VON means AP3107/H starts to work when the
voltage on HV pin is higher than VON。
VOFF means AP3107/H does not work when the
voltage on HV pin is lower than VOFF。
RBNO is the resistor between BNO pin and GND.
110
The AP3107/H integrates a lot of functions such as
green mode, frequency dithering, VCC over voltage
protection (VOVP) and line compensation. The green
mode and burst mode functions with a low operating
current could minimize the power consumed on light
load, frequency dithering will help to achieve a good
EMI result, VOVP protects the IC from being
damaged when VCC voltage is too high in abnormal
conditions, and line compensation enables a constant
over
load
protection
(OLP).
Otherwise,
over-temperature protection, soft-start function and
brown-out function are also integrated in AP3107/H,
and the brown-out range is embedded with a tight
range of 70Vac to 80Vac.
105
Brown-out Voltage (V)
100
90
85
Turn on
80
75
Turn off
70
65
60
0
30
60
90
120
150
180 210
240
270
300
330
360
BNO Resistor (kΩ)
Figure 1. Brown-out Voltage vs. BNO Resistor
The AP3107/H provides the users a high efficiency,
low standby power, minimum external component
counts and low cost solution for AC/DC power
converters especially for LCD power. The standby
power of system using AP3107/H could be less than
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95
2.2 HV Protection Resistor
HV pin is connected to the high voltage line to start
the IC, it can be connected to the line directly, but
when the lightning surge test is done, the surge
current may go through bulk capacitor positive, if
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Application Note 1057
HV pin is connected to the line directly, the lighting
noise will influence the IC by the PCB track, so one
resistor 20kΩ to 50kΩ should be connected between
high voltage line and HV pin.
2.3.2 How to Get a Constant OLP
For a constant OLP from 90Vac to 264Vac, there is
line compensation in AP3107/H and AP3106, the
current limit point with line compensation is as
below:
V cs =
136 * 10 6 (V * Ω ) − (Vin (V ) − 107 .7 (V )) * ( R ext ( Ω ) + 78850 ( Ω ))
160 * 10 6 ( Ω )
Where Rext is the resistor of RC filter for SENSE pin
in Figure 3.
Figure 4 is the curve of SENSE pin voltage vs. line
voltage when Rext=1k.
1.00
SENSE Pin Voltage (V)
0.95
Figure 2. The Resistors of HV Pin and BNO Pin
2.3 SENSE Design for AP3106 and AP3107/H
Series
2.3.1 The RC Filter Function
When switch is turned on, there will be a voltage
spike (which is caused by parasitic capacitance of
primary winding and secondary recovery current) on
the current sensing resistor. To avoid false trigger by
the voltage spike, there is 250ns LEB (Leading Edge
Blanking) time for SENSE pin, but if the time of
spike exceeds LEB time, the IC will be triggered
falsely too, so the RC filter is necessary. Otherwise
when the switch is shut down, there is a negative
voltage on current sensing resistor, and the resistor
could protect the IC from being damaged.
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0
30
60
90
120 150 180 210 240 270 300 330 360
Line Voltage (V)
Figure 4. SENSE Pin Voltage vs. Line Voltage When
Rext=1K
The formula of input power on OCP point is as the
following:
For CCM,
Pin = Vo * ( Ipeak + Itd − Icomp ) * (1 − D ) * Nt −
N t2 * Vo2 * (1 − D ) 2
Lm * fs
For DCM,
Pin =
1
( Ipeak + Itd − Icomp) 2 * Lm * fs
2
Where
Ipeak is primary peak current which is VCS/RS;
Itd is the primary current caused by delay time (td) of
IC and system which is VIN*td/LM;
Icomp is the current of line compensation on sensing
resistor;
Nt is turn ratio;
LM is primary inductor;
fs is switching frequency;
D is duty cycle.
Figure 3. RC Filter for SENSE Pin
Though RC filter is helpful to the IC, it’s time
constant should be selected carefully, because it will
affect the OCP result of system.
By the formula, we can adjust some system parameApr. 2011
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Application Note 1057
but power ground can be crossed.
ters to receive a better OLP result.
(1) Primary Inductance
Primary inductance will influence the working mode
(CCM and DCM) of system on OLP point, and it will
also decide the depth of CCM. DCM is better than
CCM on contributing to constant OLP, and deeper
CCM has a negative influence on constant OLP, so a
lower value of primary inductance will be helpful to
constant OLP.
(2) RC Filter for SENSE Pin
For RC filter, it should be adjusted on practical using,
if the line compensation is too large on high line
(OCP current on high line is lower than it on low
line), increasing RC constant is helpful to constant
OLP, if the line compensation is not enough on high
line (OCP current on high line is lower than it on low
line), decreasing RC constant is a good choice.
Figure 5. High Current Loop
3.2 ESD Design
Electro-static Discharge (ESD) is an important testing
item for switching power supply, the ability of
bearing for system could be improved by designing a
path to release the electric charge to the ground.
(3) Turn Ratio
If the line compensation is too large on high line,
decreasing turn ratio is useful for constant OLP, if the
line compensation is not enough on high line,
increasing turn ratio is a good choice.
As shown in Figure 6, the red line means the
proposed path to release the charge. A copper tip for
discharging can be placed between primary side and
secondary side, but the distance between two tips
should be consistent with the requirement of safety
specification.
3. PCB Layout for AP310X Series
3.1 EMI Consideration
A proper PCB layout can abate unknown noise
interference and EMI issue in the switching power
supply. Shown as Figure 5, there are four main huge
high frequency current loops:
The inductor of common mode filter and differential
mode filter will affect the effect of transient
discharging, so there should be copper tip with them
and the distance should be as short as possible.
Another way is placing resistor paralleled with the
inductor to replace the copper tip and the value is
about 1kΩ to 5kΩ, a smaller resistor is helpful to
ESD but has bad influence for lightning surge.
1. The current path from bulk capacitor, transformer,
MOSFET, RCS returning to bulk capacitor, path A
in Figure 5;
2. The path from GATE pin, MOSFET, RCS returning
to the ground of IC, path B in Figure 5;
3. The RCD clamp circuit is a high frequency loop,
path C in Figure 5;
4. Transformer, rectifier diode, and output capacitor
is also a high frequency current loop, path D in
Figure 5.
3.3 Common Mode Lightning Surge Design
In common mode lightning surge test, the IC pins
may observe the noisy signal which is highly
dependent on PCB design, so a good layout could
improve the ability of enduring the surge test. “Star”
connection is highly recommended for primary GND.
As shown in Figure 7, the blue lines mean separated
routines tied to GND which are connected together in
bulk capacitor negative pin. The primary side of
Y-cap can also be connected to the high voltage pin
of transformer.
They must be as short as possible to decrease the
radiation area for a better EMI, and if the MOSFET
and Schottky diode have heat sink, they should be
connected to the ground separately.
Otherwise, the IC should not be placed in the loop of
switching power trace, and control signal (low
current and low voltage) should not be across
switching power trace with pulsating high voltage,
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Application Note 1057
Figure 6. The Path to Release Charge of ESD
Figure 7. Star Connection of Primary GND
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Application Note 1057
4. How to Design a Lower Standby
Power with 3107/H
50µA current
opto-coupler.
4.1 X-capacitor and X-resistor
A good quality X-capacitor will be helpful to save the
standby power, using a low value X-cap can also
decrease the X-cap losses, according to IEC 60950,
for the X-cap exceeding 0.1µF, during an interval
equal to one constant, the voltage will have decayed
to 37% of its original value, and after calculating, the
RC value is determined by R×C<1, so for a low value
X-cap, a higher value X-resistor can be used, and the
losses on X-resistor will be reduced.
When system exits the burst mode, the output voltage
will go back to normal voltage.
4.2 Bulk Capacitor
A good quality bulk capacitor is contributed to low
standby power, it can save 20mW to 30mW power
relative to poor quality capacitor.
in
the
transistor
of
Figure 8. Resistor Paralleled with Opto-coupler
4.4 Current Sampling Resistor
The value of sampling resistor can affect the standby
power, a lower value SENSE resistor is good for low
standby power. But it is also relative to the OLP
result, a lower value SENSE resistor will make a
worse OLP result.
4.3 Opto-coupler Resistor
For a low standby power, small current mode
technology is used under light load condition. If the
system enters burst mode, the pulse of GATE pin is
low and the persistent time is over one clock, IC will
enter small current mode (the sourcing current of FB
pin is about 50µA) to reduce the power consumption
of AP3107/H, When system exits burst mode, the
AP3107/H will operate at normal current mode.
Otherwise, adjusting the opto-coupler resistor (Ropt in
Figure 8) which parallels with the opto-coupler could
affect the output voltage at small current mode. The
current (Iopt in Figure 8) flows in the diode of
opto-coupler is relative to the current of FB pin, so
Iopt will be a small current. If the current flowing in
Ropt and opto-coupler is not enough for shunt
regulator, the output voltage at small current mode
will be down from the center voltage a little, the
higher value the Ropt is, the lower value the output
voltage is, and the low output voltage will contribute
to the low standby power. The value of Ropt can be
calculated by following formula:
Ropt >
flowing
4.5 The Output Voltage Dividing Resistor
The value of output voltage dividing resistor should
be as high as possible, but the maximum value of the
resistor connected to GND (R17 in Figure 7) should
not exceed 15kΩ.
4.6 RCD Clamp Circuit
For a better standby power, the RCD clamp circuit
may be replaced by a Transient Voltage Suppressor
(TVS) and a diode (Figure 9), the advantage of the
TVS clamp is that it only conducts when it is really
needed and is independent of the switching frequency.
Compared to a RCD clamp, it reduces no-load power
but increases costs and EMI. Otherwise, a lower
value of RC is contributed to standby power, while
the voltage stress on MOSFET should be within the
spec.
Vopt × K
I c × K − I FB
Where:
Vopt is the drop voltage of diode in opto-coupler, the
normal value is about 1V;
IFB is sourcing current of FB pin at small current
mode;
IC is the minimum cathode current for regulation of
shunt regulator;
K is the current transfer rate (CTR) of opto-coupler
and the value is about 25% to 30% when there is
Apr. 2011
Figure 9. Clamp Circuit with TVS
4.7 RC Clamp on Schottky
A low value of RC which paralleled with Schottky is
helpful to low standby power, the value should
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Application Note 1057
Figure 10 shows the application schematic, and Table
2 is the test result of standby power. It shows the
LCD monitor demo board components list. The
standby power is less than 100mW in the whole input
voltage range while the load are 5V/6mA and
14V/0A, the power is measured by a power meter
Chroma 66202.
be adjusted to make the voltage stress on Shottky not
exceed the spec at turn-on.
5. LCD Monitor Demo Design and Test Result
A LCD monitor board using flyback topology is
designed, the system specification is as below:
 Output voltage and current: 14V/2.5A, 5V/2.5A
 Input voltage range: 90Vac to 264Vac
Table 2. Test Results of Standby Power (5V/6mA, 14V/0A)
Input Voltage
Input Power
90Vac/60Hz
0.057W
115Vac/60Hz
0.060W
180Vac/50Hz
0.049W
230Vac/50Hz
0.087W
264Vac/50Hz
0.095W
Figure 10. Application Circuit Schematic
Part
Value
Part
Value
Note
BD1
GUB410
C4
10pF
0805C
F1
1A/250V
C5
6.8nF
0805C
RT1
5D-9
1nF/1kV
0805C
R1, R2
2MΩ
1206R
C6，C7
C8
680µF/16V
Electrolytic
R3, R4
20kΩ
1206R
C9
680µF/10V
Electrolytic
R5
100kΩ
0805R
C10
470µF/16V
Electrolytic
R6
100kΩ
Axial-1W
C11
Electrolytic
R7
2.2Ω
1206R
C12
470µF/10V
22nF
Apr. 2011
Note
Rev. 1. 0
0805C
BCD Semiconductor Manufacturing Limited
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Application Note 1057
Part
R8
R9
R10
R11
R12
R13
R14
Value
10Ω
100kΩ
1kΩ
0.39Ω
10Ω
20Ω
150Ω
Note
0805R
0805R
0805R
Axial-1/2W
1206R
1206R
0805R
Part
CX1
CY1
L1
L2
L3
D1
D2
Value
0.22µF
1nF
30mH
2.2µH
2.2µH
FR107
1N4007
DO-41
DO-41
R15
7.5kΩ
0805R
D3
1N4148
1206
R16
20kΩ
0805R
D4
MBR10150
BCD Semi
R17
18kΩ
0805R
D5
MBR10100
BCD Semi
R18
180kΩ
0805R
U1
AP3107/H
SOIC-7
R19
12kΩ
0805R
U2
PC817C
Sharp
C1
Electrolytic
U3
AZ431
BCD Semi
C2
100µF/400V
2.2nF/1kV
Ceramic
Q1
STP6NK60Z
TO-220
C3
47µF/50V
Electrolytic
T1
ER28
Apr. 2011
Rev. 1. 0
Note
X-cap
X-cap
0.8A
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