| 摘要 |
<P>PROBLEM TO BE SOLVED: To suppress heat generation from a bipolar transistor. <P>SOLUTION: An output transistor Q1 is a PNP-type bipolar transistor, and its emitter is connected to a cathode of an LED string 6. A heat dissipation resistor R7 and a current control resistor R4 are sequentially provided in series between the emitter of the output transistor Q1 and a fixed voltage terminal. In an operational amplifier OA, its output terminal is connected to the base of the output transistor Q1, and its non-inverting input terminal is connected to the point of connection between the heat dissipation resistor R7 and the current control resistor R4, and also reference voltage Vref is applied to its inverting input terminal. A switching power supply 4 generates a drive voltage Vout so that the base potential of the output transistor Q1 agrees with the reference voltage Vref and supplies the drive voltage to the anode of the LED string 6. <P>COPYRIGHT: (C)2012,JPO&INPIT |
