Product Specification

- 10 -

R2

R1

2.1V

64uA

-12V

-5V

PWM

switching

signal

in

the

secondary

power

transformer is proportional to the AC line voltage. Adjust

the ratio of resistor divider to decide the threshold of

power-down warning. A small capacitor is connected

from UVAC to ground for filtering the switching noise.

Over Power Protection (OPP)

The OPP (over power protection) is used for

detecting over power and/or short-circuit conditions.

When OPPS voltage (p.4, Note-1) is higher than 2.1V and

this situation existed for longer than 7 msec,STC6105 will

pull the PG low and lock off the power outputs.

Vdd

OPP

OP2

OP1

R1

R2

R3

C1

Negative Voltage Protection

The NVP provides an UVP (under voltage protection)

for negative voltage outputs. An under-voltage represents

the phenomenal of the overload condition in negative

voltage output. For example, the –12V output may drop

to –10V during the overload situation. A resistor

determining the threshold of the protection is connected

from pin NVP to the negative voltage output. Via this

resistor, NVP outputs a 64uA constant current to the

negative voltage output. When the NVP voltage is over

2.1V and the situation kept for longer than 7 msec,

STC6105 will lock the power outputs off.

VNVP = 64 uA

(R1 + R2) – V-12V

The power outputs will be locked off when VNVP

2.1V.

+

UVAC

Vo

0.7V

R1

R2

C1

VS

Vin

STC6105

Power Supply Supervisor + Regulator + PWM