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TEA2262 Folha de dados(PDF) 6 Page - STMicroelectronics |
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TEA2262 Folha de dados(HTML) 6 Page - STMicroelectronics |
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6 / 9 page  GENERAL DESCRIPTION The TEA2262 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 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. TEA2262 6/9 |
Nº de peça semelhante - TEA2262 |
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Descrição semelhante - TEA2262 |
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