| ??? 07/14/05 16:58 Modified: 07/14/05 17:00 Read: times |
#97393 - 79XX are even more weird Responding to: ???'s previous message |
Jan said:
I've seen some oscillating while zero load - you cannot say what's going on then using a simple DMM. Yes. Really dangerous are the negative voltage regulators of 79XX series. With rather high negative input voltage, they show rather high minimum load current. Once I destroyed four TL082, which were supplied by a 7815/7915 pair. While 7815 behaved properly, for 7915 the supply current of 4 x 2 x 1.4mA = 11.2mA was too little. -25V baked then my circuit... I assumed the regulator to be damaged. So, was very surprised after replacing the 7915, that again a -23V was present at the OPamps! Only increasing the load current could solve the problem. So, especially if input voltage is rather high this minimum load current issue must be kept in mind. More, the 79XX is much more susceptible against lack of decoupling!! What works well with 78XX, which don't need the cap at output at all, goes totally wrong with 79XX. The 79XX series urgently needs a Tantal or at least aluminium electrolytic at output! With only 100nF oscillations of about 200kHz can be seen. Depends, of course. Kai |
| Topic | Author | Date |
| 4.7 V for at89c2051 programmer..enough? | 01/01/70 00:00 | |
| 4.7 V? | 01/01/70 00:00 | |
| load? | 01/01/70 00:00 | |
| Rise, not fall... | 01/01/70 00:00 | |
| oscillating | 01/01/70 00:00 | |
| that is the problem and still those with | 01/01/70 00:00 | |
| 79XX are even more weird | 01/01/70 00:00 | |
| 79xx - same with me | 01/01/70 00:00 | |
oscillation | 01/01/70 00:00 | |
| Thermal shut-down? | 01/01/70 00:00 | |
| get 4.91V now !! | 01/01/70 00:00 | |
| 4.91 V | 01/01/70 00:00 | |
| diode | 01/01/70 00:00 |