Datenblatt-Suchmaschine für elektronische Bauteile |
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TEA1782T Datenblatt(PDF) 7 Page - NXP Semiconductors |
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TEA1782T Datenblatt(HTML) 7 Page - NXP Semiconductors |
7 / 32 page TEA1781_82_1 © NXP B.V. 2009. All rights reserved. Preliminary data sheet Rev. 01 — 13 February 2009 7 of 32 NXP Semiconductors TEA1781T; TEA1782T GreenChip PC secondary control ICs The freewheel switch behaves like an ideal diode so the setup runs in a discontinuous mode at low loads. Negative currents are avoided by the control ICs through this switch. Replacement of the rectifying Schottky diode by two switches in anti-series allows: • Integration of the 5 V standby supply, because in Standby mode the main secondary outputs can be switched off. The supply voltages can be individually and more accurately regulated, eliminating ubiquitous post regulators. • As the output voltages is now regulated by the secondary switches, the duty cycle of the primary control switch can be kept constant, preventing ringing at the primary reset voltage. A lower reset voltage results in lower required breakdown voltages of all applied FETs, both primary and secondary. This reduces costs. • The use of Zero Voltage Switching (ZVS) at the primary side to fulfill the required standby efficiency. To fulfill the ATX12V specification on standby efficiency requirements, the system has a Standby mode in which the frequency, duty cycle and supply currents are reduced. The TEA1781T and TEA1782T are secondary control ICs. Together with the TEA1771T primary controller they form a unique system that fulfills the 80+ gold requirements at minimum costs, eliminating any cross regulation and maximizing standby efficiency. 7.2 Supply When the voltage on the primary side from the rectified input mains reaches its starting value, the primary side starts up and switches the primary main switch. From that moment, the secondary rectified transformer voltage at Vstartup, see Figure 5, is a ratio of the input voltage. Fig 5. Start-up sequence TEA1771T 014aaa185 Start-up TEA1781 TEA1782 VSTARTUP VDD Vstartup(VDD) VDD UVLO Start-up VVOUT_STB 12 V |
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