ACT413

Rev 2, 27-Feb-14

- 7 -

www.active-semi.com

Copyright © 2014 Active-Semi, Inc.

Active-Semi Proprietary―For Authorized Recipients and Customers

ActivePSR

ACT413 is a high performance peak current mode

low-voltage PWM controller IC. The controller

includes the most advance features that are

required in the adaptor applications up to 36 Watt.

Unique fast startup, frequency fold back, QR

switching technique, accurate OLP, low standby

mode operation, external compensation adjustment,

short winding protection, OCP, OTP, OVP and

UVLO are included in the controller.

Startup

Startup current of ACT413 is designed to be very

threshold level and device starts up quickly. A large

value startup resistor can therefore be used to

minimize the power loss yet reliable startup in

application. For a typical AC/DC adaptor with

universal input range design, two 1MΩ, 1/8 W

startup resistors could be used together with a VDD

capacitor(4.7uF) to provide a fast startup and yet

low power dissipation design solution.

During startup period, the IC begins to operate with

minimum Ippk to minimize the switching stresses

for the main switch, output diode and transformers.

And then, the IC operates at maximum power

‘soft-landing’ mode (decrease Ippk) to avoid output

overshoot.

Constant Voltage (CV) Mode Operation

In constant voltage operation, the ACT413 senses

the output voltage at FB pin through a resistor

divider network R5 and R6 in Figure 2. The signal

at FB pin is pre-amplified against the internal

reference voltage, and the secondary side output

voltage is extracted based on Active-Semi's

proprietary filter architecture.

This error signal is then amplified by the internal

error amplifier. When the secondary output voltage

is above regulation, the error amplifier output

voltage decreases to reduce the switch current.

When the secondary output voltage is below

regulation, the error amplifier output voltage

increases to ramp up the switch current to bring the

secondary output back to regulation. The output

regulation voltage is determined by the following

relationship:

is the rectifier diode forward drop voltage at

approximately 0.1A bias.

Constant Current (CC) Mode Operation

When the secondary output current reaches a level

set by the internal current limiting circuit, the

ACT413 enters current limit condition and causes

the secondary output voltage to drop. As the output

voltage decreases, so does the flyback voltage in a

proportional manner. An internal current shaping

circuitry adjusts the switching frequency based on

the flyback voltage so that the transferred power

remains proportional to the output voltage, resulting

in a constant secondary side output current profile.

The energy transferred to the output during each

switching cycle is ½(LP × ILIM^2) × η, where LP is

the transformer primary inductance, ILIM is the

primary peak current, and η is the conversion

efficiency. From this formula, the constant output

current can be derived:

the nominal secondary output voltage. The constant

current operation typically extends down to lower

than 40% of nominal output voltage regulation.

Standby (No Load) Mode

In no load standby mode, the ACT413 oscillator

frequency is further reduced to a minimum

frequency while the current pulse is reduced to a

minimum level to minimize standby power. The

actual

minimum

switching

frequency

is

programmable with an output preload resistor.

Loop Compensation

The ACT413 allows external loop compensation by

connecting a capacitor to extend its applications,

range.

Primary Inductance Compensation

The

ACT413

integrates

a

built-in

primary

inductance

compensation

circuit

to

maintain

constant OLP despite variations in transformer

manufacturing. The compensated ranges is +/-7%.

Primary Inductor Current Limit

Compensation

The ACT413 integrates a primary inductor peak

FUNCTIONAL DESCRIPTION

(1)

D

A

S

2

FB

1

FB

OUTCV

V

N

N

)

R

R

1

(

V

20

.

2

V

-

×

+

×

=

)

V

f

(

)

R

V

(

L

2

1

I

OUTCV

SW

2

CS

CS

p

OUTCC

×

×

×

×

=

η

(2)