| ??? 10/04/10 00:53 Modified: 10/04/10 01:44 Read: times |
#178881 - 8051 driving 2n3904 |
Hi all! Just curious as to why when I drive a 2n3904 from p3.1-6 to turn on and off an LED, everything works fine. To do the same thing to drive a 12 VDC relay, I need a 4.7K resistor in series with the base. Won't that decrease the current thereby not allowing the transistor to saturate? It works and is just driving me nuts as to why I need the 4.7K resistor. Any explanation would be appreciated!
Tom. OK. Found some info in the FAQ's. I see the need for the resistor. My relay takes 30mA to drive the coil. 4.7K makes sense. Here's the real question. My project is a North-South, East-West stop light. 6 relays, not all on at the same time, but with some dual opperation. Does the 8051 supply enough current at the P3 outputs with resistors installed and 2n3904's to drive 6 relays? 2 max on at the same time. Thanks!!! |
| Topic | Author | Date |
| 8051 driving 2n3904 | 01/01/70 00:00 | |
| NPN transistor...from port pin... | 01/01/70 00:00 | |
| The better way.. | 01/01/70 00:00 | |
| Best is to reply inline in another posting. | 01/01/70 00:00 | |
| sorry! | 01/01/70 00:00 | |
| An efficient relay driver... | 01/01/70 00:00 | |
| Zetex, RIP. | 01/01/70 00:00 | |
| 8051 driving relays | 01/01/70 00:00 | |
| Try a 'Search'. | 01/01/70 00:00 | |
Bidirectional port driver topology | 01/01/70 00:00 |