Application information

HVLED805

22/29

Doc ID 18077 Rev 1

according to the formula:

Equation 13

Equation 14

In this case the peak drain current does not depend on input voltage anymore.

µA typical).

This feature is especially important when the auxiliary winding is accidentally disconnected

and considerably increases the end-product’s safety and reliability.

5.7

Burst-mode operation at no load or very light load

When the voltage at the COMP pin falls 65 mV below a threshold fixed internally at a value,

reduced at a lower value to minimize Vcc capacitor discharge.

µs), with minimum energy transfer.

As a result of the energy delivery stop, the output voltage decreases: after 500 µs the

controller switches-on the MOSFET again and the sampled voltage on the DMG pin is

compared with the internal reference. If the voltage on the EA output, as a result of the

OFF for another 500 µs period.

In this way the converter will work in burst-mode with a nearly constant peak current defined

by the internal disable level. A load decrease will then cause a frequency reduction, which

can go down even to few hundred hertz, thus minimizing all frequency-related losses and

making it easier to comply with energy saving regulations. This kind of operation, shown in

the timing diagrams of Figure 19 along with the others previously described, is noise-free

since the peak current is low

dmg

FF

IN

SENSE

p

d

IN

R

m

R

V

R

L

T

V

⋅

⋅

=

⋅

⋅

SENSE

d

FF

p

PRI

AUX

dmg

R

T

R

L

N

N

R

⋅

⋅

⋅

=