TEA2261/0

7/11

The magnetization state of the transformer is

checked by sensing the voltage across a winding

of the transformer (generally the same which sup-

plies the TEA2261). This is made by connecting a

resistor between this winding and the demagneti-

zation sensing input of the circuit (Pin 1).

SECURITY FUNCTIONS OF THE TEA2260 (see flowchart below)

Undervoltage Detection. This protection works in

(see paragraph Starting-mode - stand-by mode). If

pulses are inhibited, in order to avoid wrong oper-

ation of the power supply or bad power transistor

drive.

(typically 15.7V) output pulses are inhibited. Re-

starting of the power supply is obtained by reduc-

Current Limitation of the Power Transistor. The

current is measured by a shunt resistor. A double

threshold system is used:

conduction of the power transistor is stopped un-

til the end of the period: a new conduction signal

is needed to obtain conduction again.

– Furthermore as long as the first threshold is

reached (it means during several periods), an ex-

2.55V) the output is inhibited. This is called the

“repetitive overload protection”. If the overload

charged, so transient overloads are tolerated.

this threshold is reached the output of the circuit

is immediately inhibited. This protection is helpful

in case of hard overload for example to avoid the

magnetization of the transformer.

Restart of the Power Supply. After stopping due

start of the power supply can be obtained by the

an integrated counter, if normal restart cannot be

obtained after three trials, the circuit is definitively

below approximately 5V to reset the circuit. From a

practical point of view, it means that the power

supply has to be temporarily disconnected from

any power source to get the restart.