| ??? 02/21/10 18:58 Read: times |
#173397 - Your circuit should work Responding to: ???'s previous message |
Your 4k7 pull-up resistor should supply 1mA base current. An hFE of 200 will produce a collector current of 200mA.
The rule of thumb is to provide 10x the necessary drive current to ensure saturation. So I would be happy for a relay coil current of 20mA. When your 8051 pin sinks current, it should starve the transistor base current. But is not the 'safest' way of designing a circuit. Especially since your relay is going to close whenever the 8051 is in RESET. If you are driving several relays you could consider the ULN280xA series. David. |
| Topic | Author | Date |
| Question on asm code | 01/01/70 00:00 | |
| 2 things | 01/01/70 00:00 | |
| some change | 01/01/70 00:00 | |
| even simpler | 01/01/70 00:00 | |
| thanks for the simplified | 01/01/70 00:00 | |
| yes, and even simpler | 01/01/70 00:00 | |
| code and comments | 01/01/70 00:00 | |
| ;; ?? | 01/01/70 00:00 | |
| thanks for the explanation | 01/01/70 00:00 | |
| Short? | 01/01/70 00:00 | |
| need some helps | 01/01/70 00:00 | |
| Your circuit should work | 01/01/70 00:00 | |
| Getting Rid Of Power On Relay Energize | 01/01/70 00:00 | |
Thank You All | 01/01/70 00:00 | |
| document what happens to ACC. | 01/01/70 00:00 | |
| noticed and questions | 01/01/70 00:00 |