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PDF AP3105NR Data sheet ( Hoja de datos )
| Número de pieza | AP3105NR | |
| Descripción | High Voltage Green Mode PWM Controller | |
| Fabricantes | BCD | |
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Application Note 1096
High Voltage Green Mode PWM Controller AP3105NA/NV/NL/NR
Prepared by Wu Qikun
System Engineering Dept.
1. Introduction
The AP3105NX is a low start-up current, current
mode PWM controller with green-mode
power-saving operation. Different from AP3103,
AP3105NX’s PWM switching frequency at normal
operation is fixed at 65kHz dithering with a narrow
range. The difference between AP3103 and
AP3105NX is shown in Table 1. The dithering of
frequency will improve EMI feature. When the load
decreases, the frequency will reduce and when at a
very low load, the IC will enter the “burst mode” to
minimize switching loss. A minimum 20kHz
frequency switching is to avoid the audible noise as
well as to reduce the standby loss. A so-called VCC
Maintain Mode is applied under light load to realize a
stable output and to reduce the loss on the start-up
resistor. The standby power of the system using
AP3105NX can be reduced to 60mW at 230V input.
Frequency
VFB Resistor
Standby
Performance
External Protection
VCC OVP
OLP & FOCP
AP3103
Adjustable
4.5kΩ
Better
NA
Auto-recoverable
Auto-recoverable
AP3105NX
Fixed at 65kHz
10kΩ
Best
By “CTRL” pin
Latch
/Auto-recoverable
Latch
/Auto-recoverable
Table 1. The Difference between AP3103/AP3105NX
The AP3105NX integrates a lot of functions such as
the Lead Edge Blanking (LEB) of the current sensing,
internal slope compensation and several protection
features which include cycle-by-cycle current limit
(OCP), fast OCP (FOCP), VCC over voltage
protection, OTP, OLP protection. The “CTRL” pin is
designed for customers to add external protection
functions such as OVP and OTP.
The AP3105NX is specially designed for off-line
AC-DC power supply, such as LCD monitors,
notebook adapters and battery charger applications. It
can offer the designers a cost-effective solution while
keeping versatile protection features. The IC uses the
SOT-23-6 package type to realize its compact size.
This application note includes detailed explanation of
the IC’s major functions, some considerations about
the PCB layout, and methods for reducing the
standby power loss, and finally presents a demo
design of a 12V 2A adaptor.
2. Function Description
2.1 CTRL Pin
For some applications, the system requires external
programmable protection function. The CTRL pin
has two kinds of modes to trigger the protection: high
level trigger and low level trigger. The low threshold
voltage is 0.5V and high threshold voltage is 2.5V.
When the CTRL pin voltage is lower than 0.5V or
higher than 2.5V, latch or auto-restart protection will
be triggered (different versions of AP3105NX offer
different protection combinations, which are shown
in Table 2).
Version
AP3105NA
AP3105NV
AP3105NL
AP3105NR
VCC
OVP
Auto-
recoverable
Latch
Latch
Auto-
recoverable
OLP&
FOCP
Auto-
recoverable
Auto-
recoverable
Latch
Auto-
recoverable
CTRL
(Low)
Latch
Latch
Latch
Auto-
recoverable
CTRL
(High)
Auto-
recoverable
Latch
Latch
Latch
Table 2. Version Classification of AP3105NX
CTRL pin voltage maintains 1.6V if the pin is
floating, so leave CTRL pin open if the designer does
not need this function. Once the latch protection is
triggered, the bulk capacitor will provide the energy
to the IC through start-up resistor to ensure the IC
disable the output signal (latch mode). This mode
will not be released until the AC input is shut off.
Therefore, the de-latch time is mainly depending on
the value of HV startup bulk capacitor. If the system
needs a short de-latch time, it is better for the startup
resistor to take power from the point before the
rectifier bridge. Typical application of CTRL pin is
shown in Figure 1.
Note:
1. The sink current to the CTRL pin should be lower
Dec. 2012 Rev. 1. 0
BCD Semiconductor Manufacturing Limited
1
1 page  
Application Note 1096
(c)
Figure 13. Driver Circuit
2.9 Start-up Circuit
A usual applied start-up circuit takes start-up current
from Bus cap (as shown in Figure 14 (b)), but the
de-latch time of some protection mode when AC
turns off will be long for the Bus cap still charges the
VCC cap.
Another start up circuit (as shown in Figure 14 (a)) is
connected ahead of bridge rectifier. It could reset
latch mode protection quickly for VCC cap have a
single larger discharge current. The de-latch time is
equal to:
tdelatch
= CVCC × Δν
I delatch
=
CVCC × 3.3V
13.6μA
CVCC is the VCC cap’s value, Idelatch is the current that
the IC consumed under protection mode. Δν is the
error of UVLO threshold and de-latch threshold.
Thus, a shorter de-latch time needs a smaller VCC
cap value.
(a)
(b)
Figure 14. Start-up Circuit
3. Standby Power Loss Reduction
Some methods are recommended here for reducing
the standby power loss.
3.1 X-capacitor and X-resistor
A good quality X-capacitor will be helpful to save the
standby power, and a low value X-cap could also
decrease the X-cap loss. According to IEC 60950, for
the X-cap exceeding 0.1μF, the voltage will be
decayed to 37% of its original value during an
interval equal to one constant, and after calculating,
the RC value is determined by the formula “R×
C<1”.
Therefore, for a low value X-cap, a higher value
X-resistor could be used, and the losses on X-resistor
will be reduced.
3.2 Current Sampling Resistor
The value of current sampling resistor could affect
the standby power. A lower value CS resistor is good
for low standby power. But it also has effects on the
OLP result: a lower value CS resistor will make a
larger OLP point.
3.3 “SENSE” Pin RC Value
The value of “SENSE” pin RC could also affect the
standby power. A larger value of RC can make the
IPEAK sense signal and the voltage on “FB” pin
smaller. A smaller voltage on“FB”pin will result in
a lower operating frequency. It is good for achieving
low standby power, but it will also make the OLP
point larger.
3.4 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 18) should
not exceed 15KΩ.
3.5 Primary RCD Clamp Circuit
To get a better standby power, the RCD clamp circuit
could be replaced by a Transient Voltage Suppressor
(TVS) and a diode (Figure 15). The advantage of the
TVS clamp is that it only conducts when necessary
and it is independent of the switching frequency.
Compared to a RCD clamp, it reduces no-load power
but increases costs and EMI. Besides, a lower value
of RC is contributed to standby power, while the
voltage stress on MOSFET should be in the spec.
Dec. 2012 Rev. 1. 0
BCD Semiconductor Manufacturing Limited
5
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| PDF Descargar | [ Datasheet AP3105NR.PDF ] | |
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