L6983IQTR datasheet(20/56 Pages) STMICROELECTRONICS

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The dependency of the isolated output voltage on the leakage is demonstrated by Figure 22, where the load

regulations with two different transformers are compared. The optimized solution implements the same inductor

of the demoboard described in section Section 11 , (ZB1346-AE, whose leakage inductance is around 1%

of the magnetizing inductance, as typically recommended). The not optimized solution consists of the use of a

transformer with a higher leakage inductance (twice as much the other transformer).

Figure 22. Effect of the transformer leakage inductance on the isolated output load regulation (VIN = 12 V,

VOUT_prim = 5 V, N = 6)

-30%

-20%

-10%

10%

20%

30%

0.05

0.1

0.15

0.2

0.25

0.3

Isolated output current [A]

Optimized leakage inductance

Not optimized leakage inductance

6.3

Efficiency

Primary output

Figure 23 shows the efficiency referred to the primary output, at two different input voltages, achieving a peak

value of almost 90%.

Figure 23. Primary output efficiency (VOUT_prim = 5 V, fSW = 400 kHz, secondary isolated output not

loaded)

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0,5

1,5

2,5

Primary output current [A]

Vin = 12 V

Vin = 24 V

90 %

≈

Figure 24 compares instead the efficiency trends depending on the switching frequency, whose effect dominates

at lower currents.

L6983I

Efficiency

DS14040 - Rev 1

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