AN4248 datasheet(10/46 Pages) STMICROELECTRONICS

10 / 46 page

Mains overvoltage shutdown

AN4248

10/46

DocID024214 Rev 1

Mains overvoltage shutdown

This feature is important to integrate in the SMPS where supply variations are quite large

and to avoid any damage to the converter ensure that the converter stops working when the

line voltage goes beyond a certain level. This can be achieved by using various pins, such

as the AC_OK , DIS OR COMP pins. In this design, we are implementing the circuit with the

AC_OK /COMP pin to retain the option of either auto restart or latched shutdown is desired.

The user can choose to use the corresponding jumper in the circuit.

Figure 5. Mains overvoltage shutdown implementation using AC_OK pin

Referring to the above circuit, with a simple bipolar BC547 and resistor divider network, we

can generate an inhibit signal to active mains OVP protection:

Vbe_sat= 0.6-0.7 V, taking typical value of 0.65 V

we have

–Vmains_OVP=300 Vac, means 300 ν2= 424 Vdc

–With RovpH= 1M, Rovp=1.5 K

Referring to the schematic, we have

–

R3 = R8 = R12 = 330 K, R16 = 1.5 K

AN4248 Datasheet(PDF) 10 Page - STMicroelectronics