| ??? 01/10/06 15:58 Modified: 01/10/06 16:00 Read: times |
#106972 - Base resistors Responding to: ???'s previous message |
Prahlad said:
4k7 wont allow 2ma to flow since Vcc=5V do I need to change the base resistor too. I would drastically decrease the base resistors to allow a saturation of transistors, like Abhishek already stated. If you still use the LPC922 in this application, you can increase the base current to up to 20mA. Then 220R resistors at the bases of BC327 transistors should be used. This should result in sufficient low collector emitter saturation voltage and in sufficient low heat dissipation. Happily only one of six transistors is on at a time... It's useful to check the collector emitter saturation voltage by the help of scope. Or select six transistors from a handful which meets lowest and nearly equal collector emitter saturation voltage. Less than 0.5V should drop at 500mA. Measure quickly, if you use a static current for selection. In any case, the transistors shouldn't become hot when running in your circuit, maximally hand warm. Solder them into the board with not too long wires (best between 3 and 5mm). But don't overheat them. By the way, are you sure, wanting about 500mA to flow through the display? Kai |
| Topic | Author | Date |
| Sourcing current to commong anode SSD. | 01/01/70 00:00 | |
| Not designed for switching purpose | 01/01/70 00:00 | |
| maybe even better | 01/01/70 00:00 | |
| Thanks for your reply erik. | 01/01/70 00:00 | |
| Oops I made serious design mistake. | 01/01/70 00:00 | |
| saturation required | 01/01/70 00:00 | |
| Try BC188 or BC640 | 01/01/70 00:00 | |
| Google fails | 01/01/70 00:00 | |
Indian creation | 01/01/70 00:00 | |
| Base resistors | 01/01/70 00:00 | |
| ULN2003 & ULN2803 | 01/01/70 00:00 | |
| Second sourced | 01/01/70 00:00 | |
| but thre aer newer "equivalents" | 01/01/70 00:00 | |
| try toyolite | 01/01/70 00:00 |