Application Note 1096
High Voltage Green Mode PWM Controller AP3105NA/NV/NL/NR
Prepared by Wu Qikun
System Engineering Dept.
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.
OLP & FOCP
Fixed at 65kHz
By “CTRL” pin
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).
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.
1. The sink current to the CTRL pin should be lower
Dec. 2012 Rev. 1. 0
BCD Semiconductor Manufacturing Limited