| ??? 02/23/06 12:58 Read: times |
#110580 - Read again my calculation example Responding to: ???'s previous message |
Sun said:
I was thinking of using a 2K ohm connected to the +15V supply in series with the 1K ohm connected to ground. This should idealy give me a 5V drop across the 1K resistor and hence the the 4.7V zener in parallel with it. With these resistor values it can not work! Please read again how I calculated the upper resistor value, then you will notice, that in your calculation neither a current through the TTL chip nor through the zener can flow! Also, it's not useful to neglect the cap in parallel to the zener. Remember, you have to deal with high frequency noise resulting from the spiky supply currents of TTL chip. So, why not using this additional cap to improve supply decoupling?? Again, why not using a simple 7805? Kai |
| Topic | Author | Date |
| Zener Turn-on-time | 01/01/70 00:00 | |
| Remedy | 01/01/70 00:00 | |
| Thank You Kai | 01/01/70 00:00 | |
| Divider | 01/01/70 00:00 | |
| Resistor values | 01/01/70 00:00 | |
| Read again my calculation example | 01/01/70 00:00 | |
| drop that stupid resistor to ground | 01/01/70 00:00 | |
| can you draw the schematic? | 01/01/70 00:00 | |
| Assistance required to post Sch | 01/01/70 00:00 | |
| If using "Windows" | 01/01/70 00:00 | |
| Typo Oops | 01/01/70 00:00 | |
| Using a cap is enough | 01/01/70 00:00 | |
| actually for the "typical" use it is not | 01/01/70 00:00 | |
| Less than 1nsec | 01/01/70 00:00 | |
| Resistor instead of the cap | 01/01/70 00:00 | |
| Sch | 01/01/70 00:00 | |
| ALWAYS design to worst case. | 01/01/70 00:00 | |
| Homepage | 01/01/70 00:00 | |
| why is that 1k still there | 01/01/70 00:00 | |
| Aha! | 01/01/70 00:00 | |
Thank you all for your help. | 01/01/70 00:00 |