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TEA2261 Datasheet(PDF) 6 Page - STMicroelectronics |
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TEA2261 Datasheet(HTML) 6 Page - STMicroelectronics |
6 / 11 page TEA2261/0 6/11 GENERAL DESCRIPTION The 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 ar- chitectures: – Master/Slave architecture. In this case, the TEA2260/61 drives the power transistor accord- ing to the pulse width modulated signals generat- ed 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 trans- former. When used in a master/slave architecture, the TEA2260/61 and also the power transistor turn-off can be easily synchronized with the line transform- er. The switching noise cannot disturb the picture in this case. As an S.M.P.S. controller, the TEA2260/61 fea- tures 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 Mode Power 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 per- centage of the nominal output voltage (e.g. 80%). To do this, the TEA2260/61 contains all the func- tions required for primary mode regulation: a fixed frequency oscillator, a voltage reference, an error amplifier and a pulse width modulator (PWM). For transmission of low power with a good efficien- cy in stand-by, an automatic burst generation sys- tem 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 Con- cept”, advantages of which are now well-known especially 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 example 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 second- ary regulator can be lower or higher than the fre- quency of the starting oscillator. The TEA2260/61 has no soft-starting system when it receives pulses from the secondary. The soft-start must be located in the secondary regula- tor. Due to the principle of the primary regulation, puls- es generated by the starting system automatically disappear when the voltage delivered by the SMPS increases. Stand-by Mode - Normal Mode Transition During 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. 1 |
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