7

LNK520

E

2/05

PI-3723-111303

R1

390 k

Ω

1/4 W

R3

15

Ω

J1

RF1

8.2

Ω

2 W

U1

LNK520P

C5

220 nF

C6

330

µF

16 V

C3

1

µF

50 V

C1

4.7

µF

400 V

D7

11DQ06

D1

1N4005

D3

1N4005

R4

6.81 k

Ω

1%, 1/4 W

1

7

6

8T

26T

100T

4

2

RTN

5.5 V, 500 mA

85 - 265

VAC

LinkSwitch

L1

1 mH

0.15 A

L

N

T1

EE16

D5

1N4007GP

C2

4.7

µF

400 V

R2

100

Ω

C4

330 pF

1 kV

5

D6B

1N4937

D2

1N4005

D4

1N4005

D

S

C

100

0

200

300

400

500

600

700

Output Current (mA)

0

1

2

3

4

5

6

7

8

9

10

85 VAC

115 VAC

190 VAC

230 VAC

265 VAC

Limits

Figure 10. 2.75 W Constant Voltage/Constant Current (CV/CC) Charger Using LinkSwitch.

Figure 11. Measured Output Characteristic of the Circuit in Figure 10.

The secondary of the transformer is rectified and filtered by

D7 and C6 to provide the DC output to the load. LinkSwitch

dramatically simplifies the secondary side by controlling both

the constant voltage and constant current regions entirely from

the primary side. This is achieved by monitoring the primary-

side bias voltage.

Diode D5, C4, R1 and R2 form the primary clamp network.

This limits the peak DRAIN voltage due to leakage inductance.

Resistor R2 allows the use of a slow, low cost rectifier diode

by limiting the reverse current through D5 when U1 turns on.

The selection of a slow diode improves radiated EMI and also

improves CV regulation, especially at no-load.