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TEA2262

SWITCH MODE POWER SUPPLY CONTROLLER

STMicroelectronics 

TEA2262

GENERAL DESCRIPTION

The TEA2262 is an off-line switch mode power

supply controller. The synchronization function and

the specific operationin stand-by mode make it well

adapted to video applications such as TV sets,

VCRs, monitors, etc...

The TEA2262 can be used in two types of architec-

tures :

- Master/slave architecture. In this case, the

TEA2262drives the power transistor according to

the pulse width modulated signals generated by

the secondary located master circuit. A pulse

transformer provides the feedback(see Figure 1).

- Conventional architecture with linear feedback

signal (feedback sources : optocoupler or trans-

former winding) (see Figure 2).

Using the TEA2262, the stand-by auxiliary power

supply, often realized with a small but costly 50Hz

transformer, is no longer necessary. The burst

mode operation of the TEA2262 makes possible

the control of very low output power (down to less

than 1W) with the main power transformer.

When used in a master/slave architecture, the

TEA2262 and also the power transistor turn-off can

be easily synchronized with the line transformer.

The switching noise cannot disturb the picture in

this case.

As an S.M.P.S. controller, the TEA2262 features

the following functions :

- Power supply start-up (with soft-start)

- PWM generator

- Direct power transistor drive (±1A)

- Safety functions : pulse by pulse current limita-

tion, output power limitation, over and under volt-

age lock-out.

S.M.P.S. OPERATING DESCRIPTION

Starting Mode - Stand By Mode

Power for circuit supply is taken from the mains

through a high value resistor before starting. As

long as VCC of the TEA2262 is below VCC start, the

quiescent current is very low (typically 0.5mA) and

the electrolytic capacitor across VCC is linearly

charged. When VCC reaches VCC start (typically

11.8V), the circuit starts, generating output pulses

with a soft-starting. Then the SMPS goes into the

stand-by mode and the output voltage is a percen-

tage of the nominal output voltage (eg. 80%).

During starting phase, in order to avoid transformer

magnetization (specially at high frequency), the

frequency oscillator is divided by four.

At switch-on, C0 charging current is divided by four.

It recover its normal value when the voltage on

soft-start capacitor reach 2.5V.

The current also recover its standard value when

the soft-start capacitor is discharged because of a

burst operating mode (starting in stand-by).

In other words, the charging current will become

and stay at its normal value, as soon as one of the

following events occurs :

- VC1 rearch 2.5V

- C1 is discharged by burst operating mode

For this the TEA2262 contains all the functions

required for primary mode regulation : a fixed fre-

quency oscillator, a voltage reference, an error

amplifier and a pulse width modulator (PWM).

For transmission of low power with a good effi-

ciency in stand-by, an automatic burst generation

system is used, in order to avoid audible noise.

Normal Mode (secondary regulation)

The normal operating of the TV set is obtained by

sending to the TEA2262 regulation pulses gener-

ated by a regulator located in the secondary side

of the power supply (TEA5170 for example).

This architecture uses the ”Master-slave Concept”,

advantages of which are now well-known espe-

cially the very high efficiency in stand-bymode, and

the accurate regulation in normal mode.

Stand-by mode or normal mode are obtained by

supplying or not the secondary regulator. This can

be ordonnered for exemple by a microprocessor in

relation with the remote control unit.

Regulation pulses are applied to the TEA2262

through a small pulse-transformer to the IN input

(pin 2). This input is sensitive to positive square

pulses. The typical threshold of this input is 0.85V.

The frequency of pulses coming from the secon-

dary regulator can be lower or higher than the

frequency of the starting oscillator.

The TEA2262 has no soft-starting system when it

receives pulses from the secondary. The soft-start-

ing has to be located in the secondary regulator.

Due to the principle of the primary regulation,

pulses generated by the starting system automat-

ically disappear when the voltage delivered by the

SMPS increases.

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