| ??? 07/03/07 17:01 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#141450 - Still no relay spec's Responding to: ???'s previous message |
A design has to begin with requirements.
In order to energize (turn-on) a relay, one has to route a certain minimal current through its input circuit (coil). Without considering that one requirement, it makes no sense to discuss anything else. The next thing to discuss is the requirements of the transistor. It has a known foward voltage when "on" (Vceo). It has a specified current gain. If the current supplied by the MCU port pin is not sufficient to provide enough current at the collector, this sort of circuit won't work. Having said that, however, it's plain that, under the stated circumstances, if the MCU gets hot, something else, very possibly unrelated to this particular circuit, is wrong. Why not go back to determine, and to design the circuit to meet, the requirements? RE |
| Topic | Author | Date |
| driving relay | 01/01/70 00:00 | |
| Base resistor | 01/01/70 00:00 | |
| Previously discussed | 01/01/70 00:00 | |
| Status LED | 01/01/70 00:00 | |
| What gets hot? | 01/01/70 00:00 | |
| relay specifications? | 01/01/70 00:00 | |
| mc gets hot | 01/01/70 00:00 | |
| What ? | 01/01/70 00:00 | |
| Reading time! | 01/01/70 00:00 | |
Still no relay spec's | 01/01/70 00:00 |