5v regulator circuit using lm105

Posted on Feb 5, 2014

A single diffused, wide base transistor like the 2N3740 is recommended because it causes fewer oscillation problems than double diffused, planar devices. In addition, it seems to be less prone to failure under overload conditions; and low cost devices are available in power packages like the TO-66 or even TO-3. When the maximum dissipation in the

5v regulator circuit using lm105
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pass transistor is less than about 0. 5W, a 2N2905 may be used as a pass transistor. However, it is generally necessary to carefully observe thermal deratings and provide some sort of heat sink. In this circuit the output voltage is determined by R1 and R2. The resistor values are selected based on a feedback voltage of 1. 8V to Pin 6 of the LM105. To keep thermal drift of the output voltage within specifications, the parallel combination of R1 and R2 should be approximately 2K. However, this resistance is not critical. Here is a schematic drawing: Variations of ±30% will not cause an appreciable degradation of temperature drift. The 1 µF output capacitor, C2, is required to suppress oscillations in the feedback loop involving the external booster transistor, Q1, and the output transistor of the LM105. C1 compensates the internal regulator circuitry to make the stability independent for all loading conditions. C3 is not normally required if the lead length between the regulator and the output filter of the rectifier is short.

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