| ??? 01/27/06 14:57 Read: times |
#108516 - valid issue, but not that, now another Responding to: ???'s previous message |
I posted:
SO, the internal diodes WILL protect the transistor, but the EMI will be dramatic if the realys are not VERY close. Kai replied: This is an interesting issue. It's often overlooked, that the diode must be faster than the transistor! I somehow doubt that Allegro used diodes that do not protect the transistors in the same package. Anyhow, coming to think about it, relying on the internal diodes in the ULN devices can be dangerous for one more reason: The inductance of the wire from V+ on the chip to the V+ on the relay will be in series with the diode and may, with a longish wire, just be enough to make the transistor go poof. So, it seem that Kai and I agree (well it does happen) that even with internal diodes it is a good idea/mandatory to have diodes at the relay. Erik |
| Topic | Author | Date |
| Relay board diagram | 01/01/70 00:00 | |
| Just search for, "Relay" !! | 01/01/70 00:00 | |
| andy Neil | 01/01/70 00:00 | |
| Relay ratings | 01/01/70 00:00 | |
| ULN2803,ULN2003 | 01/01/70 00:00 | |
| more on relay ratings | 01/01/70 00:00 | |
| Yes of course | 01/01/70 00:00 | |
| internal diodes | 01/01/70 00:00 | |
| ULN2003's doesn't easily burn | 01/01/70 00:00 | |
| Uce saturation voltage is rather high | 01/01/70 00:00 | |
| there is an alternative, search for it | 01/01/70 00:00 | |
| I agree | 01/01/70 00:00 | |
| That is bad design | 01/01/70 00:00 | |
| ULNs resist more... | 01/01/70 00:00 | |
| I would never suggest 74HC buffers for d | 01/01/70 00:00 | |
| Yes , you didn't | 01/01/70 00:00 | |
| I would like to see where that is, pleas | 01/01/70 00:00 | |
correct link | 01/01/70 00:00 | |
| Bad Design? | 01/01/70 00:00 | |
| naah | 01/01/70 00:00 | |
| Also depends on transistor speed | 01/01/70 00:00 | |
| valid issue, but not that, now another | 01/01/70 00:00 | |
| Indeed | 01/01/70 00:00 | |
| Serial | 01/01/70 00:00 | |
| How much current? | 01/01/70 00:00 | |
| allegro | 01/01/70 00:00 | |
| and infineon | 01/01/70 00:00 |