LNK406 View Datasheet(PDF) - Power Integrations, Inc

Part Name

Description

Manufacturer

LNK406

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

Power Integrations, Inc 

LNK403-409/413-419

Application Example

14 W TRIAC Dimmable High Power Factor LED Driver

Design Example

The circuit schematic in Figure 7 shows a TRIAC dimmable high

power-factor LED driver based on LNK406EG from the

LinkSwitch-PH family of devices. It was optimized to drive an

LED string at a voltage of 28 V with a constant current of 0.5 A

(±5%) ideal for PAR lamp retro-fit applications. The design

operates over a universal input voltage range of 90 VAC to

265 VAC but provides the specified output current tolerance

over a line voltage range of 90 VAC to 132 VAC (this is configurable

for high-line only applications by simple component value changes).

The key goals of this design were compatibility with standard

leading edge TRIAC AC dimmers, very wide dimming range

(1000:1, 500 mA:0.5 mA), high efficiency (>85%) and high power

factor (>0.9). The design is fully protected from faults such as

no-load, overload and output short-circuit conditions and over

temperature.

Circuit Description

The LinkSwitch-PH device (U1) integrates the power FET,

controller and start-up functions into a single package reducing

the component count versus typical implementations. Configured

as part of an isolated continuous conduction mode flyback

converter, U1 provides high power factor via its internal control

algorithm together with the small input capacitance of the

design. Continuous conduction mode operation results in

reduced primary peak and RMS current. This both reduces

EMI noise, allowing simpler, smaller EMI filtering components and

improves efficiency. Output current regulation is maintained

without the need for secondary side sensing which eliminates

current sense resistors and improves efficiency.

Input Stage

Fuse F1 provides protection from component failures while RV1

provides a clamp during differential line surges, keeping the

peak drain voltage of U1 below the 725 V rating of the internal

power FET. Bridge rectifier BR1 rectifies the AC line voltage.

EMI filtering is provided by L1-L3, C1, R16 and R17 together with

the safety rated Y class capacitor (C7) that bridges the safety

isolation barrier between primary and secondary. Resistor R16

and R17 act to damp any resonances formed between L1, L2,

C1 and the AC line impedance. A small bulk capacitor (C2) is

required to provide a low impedance source for the primary

switching current. The maximum value of C1 and C2 is limited in

order to maintain a power factor of greater than 0.9.

LinkSwitch-PH Primary

To provide peak line voltage information to U1 the incoming

rectified AC peak charges C3 via D2. This is then fed into the

VOLTAGE MONITOR pin of U1 as a current via R2 and R3. This

sensed current is also used by the device to set the line input

overvoltage and undervoltage protection thresholds. Resistor

R1 provides a discharge path for C3 with a time constant much

longer than that of the rectified AC to prevent generation of line

frequency ripple.

The VOLTAGE MONITOR pin current and the FEEDBACK pin

current are used internally to control the average output LED

current. For TRIAC phase-dimming applications a 49.9 kΩ

resistor (R4) is used on the REFERENCE pin and 4 MΩ (R2+R3)

on the VOLTAGE MONITOR pin to provide a linear relationship

between input voltage and the output current and maximizing

the dimming range. Resistor R4 also sets the internal line input

undervoltage and overvoltage protection thresholds.

F1

L 3.15 A

90 - 265

VAC RV1

275 VAC

N

R16

1 kΩ

L1

1000 µH

L2

1000 µH

R17

1 kΩ

L3

1000 µH

R9

750 kΩ

1%

BR1

2KBP06M

600 V

R10

750 kΩ

1%

R18

510 Ω

1W

C1

47 nF

275 VAC

C11

220 nF

630 V

D1

DL4002

R11

2.4 MΩ

Q1

FMMT558

C6

15 nF

50 V

VR2

ZMM5245B-7

15 V

R12

15 Ω

1%

Q2

IRFR310

R13

130 Ω

1/2 W

R1

240 kΩ

1/2 W

D2

DL4007

VR1

P6KE200A

D3

UF4007

C2

100 nF

630 V

R2

2 MΩ

1%

R3

2 MΩ

1%

C3

1 µF

400 V

D

LinkSwitch-PH

U1

LNK406EG

D4

UF4002

D5

1N4148

R5

V

3 kΩ

CONTROL

BP

S

R FB

R4

49.9 kΩ

1% C4

10 µF

16 V

11

FL1

C8 C10

330 µF 330 µF R15

50 V 50 V 20 kΩ

D8

MBRS4201T3G

1

FL2

3

2

T1

RM8

R8 D6

150 Ω DL4936

R7

10 kΩ

C5

22 µF

50 V

28 V, 500 mA

RTN

R6

162 kΩ

1%

Q3

MMBT3904

VR3

ZMM5259B-7

39 V

R19

1 kΩ

C13

100 nF

50 V

R20

10 kΩ

D7

BAV21WS-7-F

C12

1 µF

50 V

C7

2.2 nF

250 VAC

PI-5997-061510

Figure 7. Schematic of an Isolated, TRIAC Dimmable, High Power Factor, Universal Input, 14 W LED Driver.

www.powerint.com

5

Rev. D 08/11

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