Application information
L78
Figure 25: Adjustable output voltage with temperature compensation
Q2 is connected as a diode in order to compensate the variation of the Q1 VBE with
the temperature. C allows a slow rise time of the VO.
Figure 26: Light controllers (VO(min) = VXX + VBE)
Figure 27: Protection against input short-circuit with high capacitance loads
30/54
Application with high capacitance loads and an output voltage greater than 6 volts
need an external diode (see Figure 22: "Reducing power dissipation with dropping
resistor") to protect the device against input short circuit. In this case the input
voltage falls rapidly while the output voltage decrease slowly. The capacitance
discharges by means of the base-emitter junction of the series pass transistor in
the regulator. If the energy is sufficiently high, the transistor may be destroyed.
The external diode by-passes the current from the IC to ground.
DocID2143 Rev 34