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TEA2260
SWITCH MODE POWER SUPPLY CONTROLLER
TEA2260
TEA2261SWITCH MODE POWER SUPPLY CONTROLLER
June 1992 POSITIVE AND NEGATIVE CURRENT UP TO
1.2A and – 2A. LOW START-UP CURRENT. DIRECT DRIVE OF THE POWER TRANSIS-
TOR. TWO LEVELS TRANSISTOR CURRENT LIMI-
TATION. DOUBLE PULSE SUPPRESSION. SOFT-STARTING. UNDER AND OVERVOLTAGE LOCK-OUT. AUTOMATIC STAND-BY MODE RECOGNI-
TION. LARGE POWER RANGE CAPABILITY IN
STAND-BY (Burst mode). INTERNAL PWM SIGNAL GENERATOR
DESCRIPTIONThe TEA2260/61 is a monolithic integrated circuit
for the use in primary part of an off-line switching
mode power supply.
All functions required for SMPS control under nor-
mal operating, transient or abnormal conditions are
provided.
The capability of working according to the "master-
slave" concept, or according to the "primary regu-
lation" mode makes the TEA2260/61 very flexible
and easy to use. This is particularly true for TV
receivers where the IC provides an attractive and
low cost solution (no need of stand-by auxiliary
power supply). See application note AN376/0490
for detailed information.
PIN CONNECTIONS1/9
Figure 1 : Master-slave Concept
Figure 2 : Secondary Regulation (with optocoupler)
SIMPLIFIED APPLICATION DIAGRAMS
TEA2260 - TEA22612/9
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
THERMAL DATA 100 1500
P (W)tot4
MAXIMUM POWER DISSIPATION
TEA2260 - TEA22613/9
RECOMMENDED OPERATING CONDITIONS
ELECTRICAL CHARACTERISTICS (Tamb = 25o C, VCC =12V, unless otherwise specified)
POWER SUPPLY
OSCILLATOR / PWM SECTION
ERROR AMPLIFIER SECTION
INPUT SECTION
CURRENT LIMITATION SECTION
TEA2260 - TEA22614/9
GENERAL DESCRIPTIONThe TEA2260/61 is an off-line switch mode power
supply controller. The synchronization function and
the specific operation in stand-by mode make it well
adapted to video applications such as TV sets,
VCRs, monitors, etc...
The TEA2260/61 can be used in two types of
architectures : Master/slave architecture. In this case, the
TEA2260/61 drives the power transistor accord-
ing to the pulse width modulated signals gener-
ated 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 TEA2260/61, 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 TEA2260/61 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
TEA2260/61 and also the power transistor turn-off
can be easily synchronized with the line trans-
former. The switching noise cannot disturb the
picture in this case.
As an S.M.P .S. controller, the TEA2260/61 features
the following functions : Power supply start-up (with soft-start) PWM generator Direct power transistor drive (+1.2A, -2.0A) 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 ModePower for circuit supply is taken from the mains
through a high value resistor before starting. As
long as VCC of the TEA2260/61 is below VCC start,
the quiescent current is very low (typically 0.7mA)
and the electrolytic capacitor across VCC is linearly
charged. When VCC reaches VCC start (typically
10.3V), 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%).
For this the TEA2260/61 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 TEA2260/61 regulation pulses gen-
erated by a regulator located in the secondary side
of the power supply.
This architecture uses the "Master-slave Concept",
advantages of which are now well-known espe-
cially the very high efficiency in stand-by mode, 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 TEA2260/61
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 TEA2260/61 has no soft-starting system when
it receives pulses from the secondary. The soft-
starting has to be located in the secondary regula-
tor.
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.
Stand-by Mode - Normal Mode TransitionDuring the transition there are simultaneously
pulses coming from the primary and secondary
regulators.
These signals are not synchronized and some care
has to be taken to ensure the safety of the switching
power transistor.
A very sure and simple way consist in checking the
transformer demagnetization state. A primary pulse is taken in account only if the
transformer is demagnetized after a conduction
of the power transistor required by the secondary
regulator. A secondary pulse is taken in account only if the
transformer is demagnetized after a conduction
of the power transistor required by the primary
regulator.
With this arrangement the switching safety area of
the power transistor is respected and there is no
risk of transformer magnetization.
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).
TEA2260 - TEA22615/9
SECURITY FLOW-CHART (TEA2260)
SECURITY FUNCTIONS OF THE TEA2260 (see flow-chart below) Undervoltage detection. This protection worksin association with the starting device "VCC
switch" (see paragraph Starting-mode - standby
mode). If VCC is lower than VCCstop (typically
7.4V) output pulses are inhibited, in order to avoid
wrong operation of the power supply or bad
power transistor drive.
Overvoltage detection. If VCC exceeds VCCmax(typically 15.7V) output pulses are inhibited. Re-
starting of the power supply is obtained by reduc-
ing VCC below VCCstop.
Current limitation of the power transistor. Thecurrent is measured by a shunt resistor. A double
threshold system is used : When the first threshold (VIM1) is reached, the
conduction of the power transistor is stopped
until 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
external capacitor C2 is charged. When the
voltage across the capacitor reaches VC2 (typi-
cally 2.55V) the output is inhibited. This is called
the "repetitive overload protection". If the over-
load diseappears before VC2 is reached, C2 is
discharged, so transient overloads are toler-
ated. Second current limitation threshold (VIM2).
When this threshold is reached the output of the
circuit is immediatly inhibited. This protection is
helpfull in case of hard overload for example to
avoid the magnetization of the transformer.
Restart of the power supply. After stopping dueto VC2, VIM2, VCCMax or VCCstop triggering, re-
start of the power supply can be obtained by the
normal operating of the "VCC switch" but thanks
to an integrted counter, if normal restart cannot
be obtained after three trials, the circuit is defini-
tively stopped. In this case it is necessary to
reduce VCC below approximately 5V to reset the
circuit. From a practical point of view, it means
that the power supply has to be temporarily dis-
connected from any power source to get the
restart.
TEA2260 - TEA22616/9
