| ??? 01/21/05 08:50 Read: times |
#85469 - Opto Responding to: ???'s previous message |
Sun Din said:
An opto-coupler is providing the input, with the collecter tied High "1" and the emitter connected to the pin. I thought that when the opto is off the input will float so I used a pull down resistor. Does the opto have PNP or NPN output? For NPN, you would normally ground the emitter, and put a load resistor in the collector circuit. This forms a classic common emitter connection, in which the base current is provided by the light signal within the opto isolator. To calculate the required collector load, you need to read the opto Datasheet and look at the current transfer ratio. |
| Topic | Author | Date |
| Inputs | 01/01/70 00:00 | |
| Opto | 01/01/70 00:00 | |
| Opto input | 01/01/70 00:00 | |
| Optocoupler Designer’s Guide | 01/01/70 00:00 | |
| What type of opto? | 01/01/70 00:00 | |
| pulling high | 01/01/70 00:00 | |
| Why??? | 01/01/70 00:00 | |
| Misleading.... | 01/01/70 00:00 | |
| OK, clearer | 01/01/70 00:00 | |
| I must be stupid... | 01/01/70 00:00 | |
| you are not | 01/01/70 00:00 | |
| Heres Why | 01/01/70 00:00 | |
| Not quite so. | 01/01/70 00:00 | |
| Pull-downs must be much smaller! | 01/01/70 00:00 | |
| OK you are right. | 01/01/70 00:00 | |
A little history | 01/01/70 00:00 | |
| Link... | 01/01/70 00:00 | |
| use opto-coupler as NPN | 01/01/70 00:00 | |
| Thank you All, & a question for Kai | 01/01/70 00:00 | |
| Opto to pull-down signal | 01/01/70 00:00 |