Bidirectional_MOSFET_switch_controllers

Published:2009/7/24 20:50:00 Author:Jessie | From:SeekIC

Figures 8-51 and 8-52 show manual and automatic bidirectional switches, respectively. Such circuits are used when the supply voltage is higher or lower than the load voltage, when powered by a secondary source. In the manual circuit of Fig. 8-51, 51 disconnects the battery from both the load and source when VIN (from a wall-unit power supply) is connected. This permits the load voltage to fluctuate above or below the battery voltage, without forcing current into (or out of) the battery. In the far more practical automatic circuit of Fig. 8-52, Q1 and Q2 fully disconnect the battery from the load immediately after the wall-unit supply is connected to VIN. The two diodes in Q1 and Q2 are also connected back to back, and no current can flow through the switch when the gate drive is removed. The LTC1154 EN (enable) input senses when the wall-unit voltage exceeds 3 V, and inverts the switch action so that Q1/Q2 are turned off when the wall-unit supply is disconnected. LINEAR TECHNOLOGY, APPLICATION NOTE 53, P. 3.



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