ACT411

Rev 4, 27-Feb-14

www.active-semi.com

Copyright © 2014 Active-Semi, Inc.

- 8 -

ActivePSR

current limit compensation circuit to achieve

constant OLP over wide line and wide load range.

Output Cable Resistance Compensation

The ACT411 provides internal programmable

output cable resistance compensation during

constant voltage regulation, monotonically adding

an output voltage correction up to predetermined

percentage at full power.

The feature allows better output voltage accuracy

by compensating for the output voltage drop due to

the output cable resistance.

Frequency Fold-back

When the load drops to 75% of full load level,

ACT411 starts to decrease the switching frequency,

which is proportional to the load current ,to improve

the efficiency of the converter as show in Functional

Block Diagram.

This enables the application to meet all latest green

energy standards. The actual minimum switching

frequency is programmable with a small dummy

load (while still meeting standby power).

Valley Switching

ACT411 employed valley switching from medium

load to heavy load to reduce switching loss and

EMI. After the switch is turned off, the ringing

voltage from the auxiliary winding is applied to the

VFB pin through feedback network R5, R6.

Internally, the VFB pin is connected to an zero-

crossing detector to generate the switch turn on

signal when the conditions are met. In light load, the

frequency fold back scheme starts to take control to

determine the switch turn on signal, so thus the

switching frequency.

Figure 1:

Valley Switching at heavy load

Protection Features

The ACT411 provides full protection functions. The

following table summarizes all protection functions.

Auto-Restart Operation

ACT411 will enter auto-restart mode when a fault is

identified. There is a startup phase in the auto-

restart mode. After this startup phase the conditions

are checked whether the failure is still present.

Normal operation proceeds once the failure mode is

removed. Otherwise, new startup phase will be

initiated again.

To reduce the power loss during fault mode, the

startup delay control is implemented. The startup

delay time increases over lines.

Over Load Protection (OLP)

When the secondary output current reaches a level

set by the internal current limiting circuit, the

ACT411 enters current limit condition and causes

the secondary output voltage to drop, the IC enters

fault mode and enter auto restart mode.

ACT411 is able to achieve very accurate OLP

primary inductor values.

Short Circuit Protection

When the secondary side output is short circuited,

the ACT411 enters hiccup mode operation. This

hiccup behavior continues until the short circuit is

removed.

FUNCTIONAL DESCRIPTION CONT’D

Vdrain_gndMosfet

t

DCvoltage

T

Ton

Possible Valley turn on

PROTECTION

FUNCTIONS

FAILURE

CONDITION

PROTECTION

MODE

(4 duty cycle)

Auto Restart

Over Temperature

T > 135˚C

Auto Restart

Short Winding/

Short Diode

Auto Restart

Over Load

Auto Restart

Output Short

Circuit

Auto Restart

Open Loop

No switching for

4 cycle

Auto Restart

Voltage

Auto Restart

VFB Over Voltage

(4 duty cycle)

Auto Restart