| ??? 05/25/06 04:00 Modified: 05/25/06 04:05 Read: times |
#117063 - You are experienced, I see... Responding to: ???'s previous message |
Richard said:
If one manages the dissipation by means of a series resistor on the input, which is quite simple, and which is recommended in one of the many app-notes, which, back then, were generally quite correct and reliable, one can avoid the trouble. I do also use series resistors in front of these regulators, mostly as part of a pi-filter. Richard said:
Linear regulators like to have a series resistor at the input anyway, though I prefer to put them upstream of the primary filter cap, since that protects the rectifier diodes, too. It doesn't save any heat, but it helps the regulator. Ah, I see you are an experienced developer! With standard transformers, you know the ones showing rather high overvoltages ("idle voltage"? In german "Leerlaufspannung") when being unloaded, secondary windings often provide enough ohmic resistance to limit surge currents to sane values even without additional resistors. But with toroid transformers, which are much more stiff, an added resistance of some 1/10 of Ohms to some Ohms can be helpful indeed! Interesting to note, that the obligatory fuses to be used with transformers and which must be connected at the secondary windings (mostly) since 1996, do also provide useful surge current limitation, as if you had added a resistor. Richard said:
I also like to use a preregulator... I do also like preregulators. I often use LM2674 (high efficiency switcher) in front of LM7805 to fabricate a voltage of about +8.5V. This keeps the overall heat dissipation very low, while at the same time providing lots of headroom, when the mains voltage shows undervoltage. Kai |
| Topic | Author | Date |
| smps/linear ps. | 01/01/70 00:00 | |
| the moon is in the 3rd quarter | 01/01/70 00:00 | |
| Post circuit diagram | 01/01/70 00:00 | |
| Break of GND line? | 01/01/70 00:00 | |
| Maybe he's forgotten the caps? | 01/01/70 00:00 | |
| Any connection to Phone line ? | 01/01/70 00:00 | |
| Have you examined the linear PS? | 01/01/70 00:00 | |
| one caveat | 01/01/70 00:00 | |
| granted, but that's a misapplication. | 01/01/70 00:00 | |
| his question is why does it fail with 78 | 01/01/70 00:00 | |
| True enough, but until he does the work | 01/01/70 00:00 | |
| as usual | 01/01/70 00:00 | |
| Natural enemy | 01/01/70 00:00 | |
| Quite true, Kai | 01/01/70 00:00 | |
| You are experienced, I see... | 01/01/70 00:00 | |
| I just wonder | 01/01/70 00:00 | |
| When I need a clean signal | 01/01/70 00:00 | |
| but then you have to clean up | 01/01/70 00:00 | |
| Fuse in secondary circuit. | 01/01/70 00:00 | |
| Fuses | 01/01/70 00:00 | |
| Slow-blo? | 01/01/70 00:00 | |
Yes, but... | 01/01/70 00:00 | |
| schematic | 01/01/70 00:00 | |
| no schematic here ... ??? | 01/01/70 00:00 |