| ??? 11/25/10 15:03 Read: times |
#179614 - Switch off a LED array |
Given below is a scheme of a LED array used to check out a Digital Output section of a PCI card. The current limiting resistors are all 2.2K for each LED.
Everything is fine when the outputs are driven high and the LEDs glow well. But the problem happens when the output bits are driven low when there is a voltage of about 4V on the pins. Unfortunatley this low voltage specfication is between 0 to 4 V DC and its a matter of chance which one lands in your hands ! My problem is to COMPLETELY switch OFF the LEDs at 4 V as currently they all glow, albeit dull. This makes it difficult to use the simulator. Increasing the current limiting resistor is not a good way as it affects the HIGH level glow. Tried a 3V zener in series but of no use. While there are solutions like interposing a 24V relay, I am looking for a simple solution as the simulator is already made ! 
Thanks Raghu |
| Topic | Author | Date |
| Switch off a LED array | 01/01/70 00:00 | |
| What are the switches? | 01/01/70 00:00 | |
| Virtual ground at 3.3V | 01/01/70 00:00 | |
| 3.3V Regulator Idea | 01/01/70 00:00 | |
| The 3.3V regulator idea might not work! | 01/01/70 00:00 | |
| It is a SOURCE board ... | 01/01/70 00:00 | |
| Hhm, leakage currents? | 01/01/70 00:00 | |
| Solution in sight | 01/01/70 00:00 | |
| LED tester shows bad design/bad parts | 01/01/70 00:00 | |
| Who is the designer ?? Stand up.... | 01/01/70 00:00 | |
| LED tester shows bad design/bad parts | 01/01/70 00:00 | |
| I wouldn't rely on anything published by NI | 01/01/70 00:00 | |
| crying wolf again?? | 01/01/70 00:00 | |
| NI is not a fly-by-night-operator | 01/01/70 00:00 | |
| No question about that | 01/01/70 00:00 | |
| The "crying wolf" is right here... | 01/01/70 00:00 | |
| I also say it... | 01/01/70 00:00 | |
Leakage current analysis | 01/01/70 00:00 | |
| Also, the voltage across the load.... | 01/01/70 00:00 |