| ??? 10/04/10 01:43 Read: times |
#178883 - The better way.. Responding to: ???'s previous message |
You have been trying out an NPN driver circuit. Such circuit should be like this:
Do note though that the standard type 8051 type I/O pin is not so good at driving high. The internal weak pullup is a poor excuse as a good drive for an NPN transistor. The port pins do far better when pulling down to a low level. For this reason a PNP transistor as in the following circuit is a far better choice, even for driving an LED. 
Since you are trying to drive a 12V RELAY the best situation is to combine the PNP idea at the port pin with the NPN to drive the relay as shown below: 
These circuits that use a PNP transistor off the port pin also have the added advantage they stay off at initial power on so there is no glitch of the relays until such time that the software in the MCU gets things initialized. Michael Karas |
| 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 |