Application information

HVLED001B

28/33

DS12748 Rev 2

7.6

Protections

A comprehensive set of protections is embedded to ensure a high level of reliability of the

final application using a limited number of components.

7.6.1

Over current protection (OCP)

To prevent any damage to active components in case of inductor saturation the MOSFET is

immediately turned off by fast OCP protection. On this occurrence the IC temporarily enters

stop state for a time equal to TOCP.

7.6.2

Input over voltage protection (I-OVP)

Disturbances of the input voltage like surges or bursts may increase the voltage applied to

the transformer primary side. At worst, an excessive input voltage could be applied to the

application. These occurrences may result in MOSFET damage during the OFF state when

the drain voltage rises to Vin plus reflected voltage, eventually above the maximum absolute

rating of the MOSFET itself.

An input voltage higher than VSurge, measured by the HVSU structure, immediately stops

the IC. An internal hysteresis improves the noise rejection of this feature. This protection is

always active.

7.6.3

Brownout protection (BO)

The current sourced by the ZCD pin's negative clamp during ON-time is compared to a

minimum value to determine whether the input voltage is lower than the input range

specification (Brownout protection). If a value lower than IBO for a time longer than TBO,

managed by the ART, is detected, the IC is stopped for Trec and then restarted.

When the protection is triggered, the ART performs the auto-relaoding procedure after Trec.

Brownout protection is active during active mode, but blanked during ramp-up mode.

Referring to the typical application schematic, the brownout level can be obtained adjusting

the transformer turn ratio and ZCD resistor configuration. The following equation regulates

the relationship between said level and external components.

Equation 3

7.6.4

Over power protection (OPP)

This protection detects either the over-load condition or the absence of the optocoupler

control (no pull-down) or for more than a time equal to TOPP and switches off the

application putting the device in low consumption mode. This prevents the output power

from rising above excessive values due to the loss of control.

The ART manages the TOPP interval and performs the auto-reloading procedure after Trec.

The OPP is active during active mode, but blanked during ramp-up mode.

Vbrown,out

+

 I

BO



=