LNK408 데이터 시트보기 (PDF) - Power Integrations, Inc

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LNK408

Single-Stage PFC, Primary-Side Constant Current Control and TRIAC Dimming/Non-Dimming Options

Power Integrations, Inc 

LNK403-409/413-419

D

V

CONTROL

BP

S

R FB

Over-Current Protection

The current limit circuit senses the current in the power FET.

When this current exceeds the internal threshold (ILIMIT), the power

FET is turned off for the remainder of that cycle. A leading edge

blanking circuit inhibits the current limit comparator for a short

time (tLEB) after the power FET is turned on. This leading edge

blanking time has been set so that current spikes caused by

capacitance and rectifier reverse recovery will not cause

premature termination of the power FET conduction.

PI-5435-052510

Figure 6. Remote ON/OFF VOLTAGE MONITOR pin Control

5.9 V Regulator/Shunt Voltage Clamp

The internal 5.9 V regulator charges the bypass capacitor

connected to the BYPASS pin to 5.9 V by drawing a current

from the voltage on the DRAIN pin whenever the power FET is

off. The BYPASS pin is the internal supply voltage node. When

the power FET is on, the device operates from the energy

stored in the bypass capacitor. Extremely low power

consumption of the internal circuitry allows LinkSwitch-PH

to operate continuously from current it takes from the DRAIN

pin. A bypass capacitor value of 10 or 100 mF is sufficient for

both high frequency decoupling and energy storage. In

addition, there is a 6.4 V shunt regulator clamping the BYPASS

pin at 6.4 V when current is provided to the BYPASS pin

through an external resistor. This facilitates powering of

LinkSwitch-PH externally through a bias winding to increase

operating efficiency. It is recommended that the BYPASS pin is

supplied current from the bias winding for normal operation.

Auto-Restart

In the event of an open-loop fault (open FEEDBACK pin resistor

or broken path to feedback winding), output short-circuits or an

overload condition the controller enters into the auto-restart

mode. The controller annunciates both short-circuit and

open-loop conditions once the FEEDBACK pin current falls

below the IFB(AR) threshold after the soft-start period. To

minimize the power dissipation under this fault condition the

shutdown/auto-restart circuit turns the power supply on (same

as the soft-start period) and off at an auto-restart duty cycle of

typically DCAR for as long as the fault condition persists. If the

fault is removed during the auto-restart off-time, the power

supply will remain in auto-restart until the full off-time count is

completed. Special consideration must be made to appropriately

size the output capacitor to ensure that after the soft-start

period (tSOFT) the FEEDBACK pin current is above the IFB(AR)

threshold to ensure successful power-supply start-up.

After the soft-start time period, auto-restart is activated only

when the FEEDBACK pin current falls below IFB(AR).

Line Under/Overvoltage Protection

This device includes both line under- and overvoltage detection

to limit the minimum start-up and maximum operating voltage

detected through the VOLTAGE MONITOR pin. An external peak

detector consisting of a diode and capacitor are required to

provide input line peak voltage to the VOLTAGE MONITOR pin

through a resistor. At power up, IUV+ keeps the LinkSwitch-PH

off until the input line voltage reaches the undervoltage threshold.

At power down, IUV- prevents restart attempts after the output

goes out of regulation.

The same resistor used for UV also sets line overvoltage (OV)

shutdown threshold which, once exceeded, forces the

LinkSwitch-PH to stop switching (after completion of the current

switching cycle). Once the line voltage returns to normal, the

device resumes normal operation. A small amount of hysteresis

is provided on the OV threshold to prevent noise triggering.

When the power FET is off, the rectified DC high voltage surge

capability is increased to the voltage rating of the power FET

(725 V), due to the absence of the reflected voltage and leakage

spikes on the drain.

Hysteretic Thermal Shutdown

The thermal shutdown circuitry senses the controller die

temperature. The threshold is set at 142 °C typical with a 75 °C

hysteresis. When the die temperature rises above this threshold

(142 °C) the power FET is disabled and remains disabled until

the die temperature falls by 75 °C, at which point the power FET

is re-enabled.

Safe Operating Area (SOA) Protection

The device also features a safe operating area (SOA) protection

mode which disables FET switching for 40 cycles in the event

the peak switch current reaches the ILIMIT threshold and the

switch on-time is less than tON(SOA). This protection mode

protects the device under short-circuited LED conditions and at

start-up during the soft-start period when auto-restart protection

is inhibited. The SOA protection mode remains active in normal

operation.

4

Rev. D 08/11

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