31/42

AN1262 APPLICATION NOTE

The optimum value will be found empirically once the transformer construction has been frozen. Also the divider

bench verification. Some improvement in terms of load regulation can be achieved by using an inductor (typi-

cally, between 1 and 10

µH) instead of a resistor. Any inexpensive axial inductor able to carry few mA will serve

the purpose.

Figure 17. Leading Edge Blanking (LEB) circuit for leakage inductance spikes filtering

However, the most effective way to improve regulation is to use the circuit shown in figure 17, which blanks the

spike appearing at the leading edges of the voltage generated by the self-supply winding. This spike, due to the

transformer's leakage inductance, is the major responsible for the poor load regulation.

18

LAYOUT RECOMMENDATIONS

A proper printed circuit board (PCB) layout is essential for correct operation of any switch-mode converter and

this is true for the devices of the L6590 family as well. Careful component placing, correct traces routing, appro-

priate traces widths and compliance with isolation distances are the major issues.

Figure 18. Suggested ground routing for converters with secondary feedback.

Vcc

GND

L6590

L6590D

L6590A

1N4148

BC327

10 k

Ω

100 pF

22 µF

Iout [A]

Vout [V]

0.01

0.1

1

11

12

13

14

15

16

17

18

Rs

LEB

Vin

Vout

L6590

L6590D

L6590A

DRAIN

GND

COMP

Vcc

Vac

VFB

Primary Power GND

Secondary Signal GND

Primary Signal GND

One-point GND

BOK

Secondary Power GND

L6590A and

L6590D only

L6590 and

L6590D only

C

Y1