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STCH02 датащи(PDF) 3 Page - STMicroelectronics |
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STCH02 датащи(HTML) 3 Page - STMicroelectronics |
3 / 24 page DocID028766 Rev 1 3/24 STCH02 Device description and block diagram 24 1 Device description and block diagram The STCH02 is a current mode controller designed for offline quasi resonant ZVS (zero voltage switching at switch turn-on) flyback converters. It combines a high performance low voltage PWM controller chip and a 650 V HV start-up cell in the same package. The device features a unique characteristic: it is capable to provide a constant output current (CC) regulation using primary-sensing feedback. This eliminates the need for a dedicated current reference IC, as well as the current sensor, still maintaining a quite accurate output current regulation. The quasi resonant operation is achieved by means of a transformer demagnetization sensing input that triggers MOSFET's turn-on, connected on the ZCD pin. This input serves also to monitor the output voltage monitor and to achieve the mains independent CC regulation (line voltage feedforward). The maximum switching frequency is top-limited below 260 kHz, so that at the medium- light-load a special function automatically lowers the operating frequency still maintaining the operation as close to ZVS as possible. At the very light-load, the device enters a controlled burst mode operation that, along with the zero power high voltage start-up circuit, the extremely low quiescent current of the device, helps minimize the residual input consumption, thus meeting the requirements of the most stringent standards. During the CC regulation, where the flyback voltage generated by the auxiliary winding drops and may be not enough to supply the internal circuits, the chip is able to power itself directly from the rectified mains through the high voltage start-up circuit. During the burst mode operation the self-supply feature is disabled (due to very stringent no load consumption requirement), and the VDD supply voltage has to be guaranteed by proper application design. In any case, an innovative adaptive UVLO helps minimize the issues related to the fluctuations of the self-supply voltage with the output load, due to transformer's parasitic and further reducing the IC's bias consumption. In addition to the said functions that optimize power handling under different operating conditions, the device offers also a protection against the transformer saturation and secondary diode short-circuit and an adjustable output overvoltage protection. All of them are in the autorestart mode. An embedded leading edge blanking on the current sense input for greater noise immunity completes the equipment of this device. |
Аналогичный номер детали - STCH02 |
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Аналогичное описание - STCH02 |
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