CURRENT_LIMITING_A_SERIES_REGULATOR

Published:2009/7/13 3:07:00 Author:May | From:SeekIC

If the current limitation of the series-pass transistor is exceeded, transistor Q1 could be damaged or destroyed. This can be prevented with the addition of a current-limiting transistor, as shown in the figure. When the current through Q1 becomes high enough, the voltage drop across R2 becomes high enough to forward-bias transistor Q2. When Q2 starts to conduct, its internal resistance decreases. When this occurs, the forward bias of Q1 is fixed, and its output is a constant current. The current-limiting transistor and resistor in the figure protect the pass transistor and rectifier diodes if the load terminals are accidentally short-circuited. However, the addition of transistor Q2 increases the already high power dissipation in pass transistor Q1 when the load demand is high.



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