| ??? 01/10/06 04:22 Read: times |
#106947 - Oops I made serious design mistake. Responding to: ???'s previous message |
Dear Kai,
Thanks for your reply, I didnt read the datasheet carefully and couldnt notice that 100mA limit. My schematic is as shown below. The resistor at outputs of 74LS541 are 47 Ohms and those at base of BC557 are 4k7. I will change the transistors with BC327 in my design. Do you see any more design mistakes. - hfe minmum for BC327 is 100. - Vf [ LED ] = 1.8V - 8 Segments including decimal will take approx. 150 to 200mA. - Base current = 200mA / ( 100 ) = 2mA. 4k7 wont allow 2ma to flow since Vcc=5V do I need to change the base resistor too. Please help me. 
Thanks & Regards, Prahlad Purohit |
| 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 |