| ??? 01/24/06 12:59 Read: times |
#108170 - Better use a PNP transistor Responding to: ???'s previous message |
when i connected the port output to base of bc548 transistor to amplify and connected one lead of led to collector and another to vcc.and emitter is grounded You need a current limiting resistor between LED and collector of transistor. What probably happened is, that too high LED current damaged transistor causing a short circuit within collector emitter path, permanently allowing current to flow through the LED. It's not a good idea to drive the LED by the help of NPN transistor, because port output cannot deliver much current when emitting logic high. It's better to use a PNP transistor: Connect the emitter to 5V, base to port output via 10k resistor, anode of LED to collector, cathode of LED to 330R resistor and finally other side of this resistor to ground. Kai |
| Topic | Author | Date |
| port problem | 01/01/70 00:00 | |
| here | 01/01/70 00:00 | |
Better use a PNP transistor | 01/01/70 00:00 |