L4990 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

MFG CO.

L4990

PRIMARY CONTROLLER

STMicroelectronics 

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ing conditions range, in terms of input voltage and

output current, that the converter is able to cover

but, on the other hand, the higher is the peak cur-

rent on the secondary side.

As to this point, the L4990 turns out to be particu-

larly useful since it allows to set any maximum

duty cycle greater (and lower) than 50% with very

good precision. In the present case, a maximum

duty cycle of 60% for steady state operation has

been selected and an extra 5% is allowed to take

transients into account.

Since it is not requested a very tight tolerance on

the output, the feedback employs a primary side

voltage sensing technique to reduce cost and

complexity of the circuit. The same technique has

been used to protect against output overvoltages.

The electric schematic is shown in fig. 30. The

PCB layout is shown in figg. 31 and 32. Table 1

and 2 summarize typical system performance,

while table 3 lists the relevant bill of material,

where details are given only for critical compo-

nents and/or where useful.

Warning: the NTC for inrush current limitation is

not assembled, thus use caution when connecting

the demo board to the mains directly. The use of

a variac or an isolation transformer is recom-

mended.

Figure 30. AC-DC adaptor electric schematic

L4990 - L4990A

Table 1. System efficiency.

Vin (Vac)

85

110

220

270

Iout = 1A

Vout (V)

14.93

Effic. %

83.7

14.95

82.5

14.95

81.4

14.96

76

Iout = 2A

Vout (V)

14.53

Effic. %

84.3

14.55

84.9

14.57

85.2

14.59

81.6

Table 2. System performance.

Line regulation

Load regulation

Iout = 0.5A to 2A

Maximum effic.

Output ripple

Minimum load

Transition Volt.

Vin = 85 to 270 Vac

Iout = 0.5A

Vin = 85 Vac

Vin = 270 Vac

Vin = 190 Vac

Iout = 2A

Vin = 85 to 270 Vac

Iout = 2A

Vin = 270 Vac

Vout < 20V

From C.C.M to D.C.M

Iout = 2A

30mV

0.95V

0.90V

86.2%

< 200mV

150mA

160V

85 to

270

Vac

R1

NTC

B1

C1

R2

R15

R12

R20

C8

T1

R19

D4

R13

R21

D3

R14

D2

R5

C10

R6

C3

R4

C7

R3

VFB

COMP

DIS

VCC VC

OUT

R7

R8

DCC 5

6 14

8

9 10

Q1

3

R9

VREF

4

L4990

ISEN

R24

13

R11

2

7

12 15

11

R10 RCT

SS DC-LIM

SGND PGND

C4

C5

C6

C11

R23

Q2

C15

R22

C14

C12

R16

D1

C2

C13

D97IN499B

15V/2A

R17

GND

15/24

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