| ??? 11/06/09 15:47 Read: times |
#170506 - Indeed! Responding to: ???'s previous message |
Ap said:
Producing 3.3V from 5V using LM317 is an instable and un reliable procedure ,dont use LM317 but use an LDO . Look datasheet of LM317 carefully. The drop out voltage of an LM317 is higher compared to 78XX series. According to datasheet at 200mA a dropout voltage of 1.7V must be expected typically, corresponding to an output voltage change of 100mV. This means, as Erik already told, that the regulator is out of regulation, at least partially. But, this is only true for a junction temperature of 25°C. When dissipating heat, namely 1.7V x 200mA = 340mW, the junction temperature rises by about 0.34W x 50K/W = 17K, if a TO220 package is used and isn't cooled. This results in a decrease of dropout voltage again to about 1.6V. So, situation is just on the rocks... Well, Raj can check the regulated voltage with a scope and see, whether this is actually the reason of malfunctioning. I would give the LF33CV a try. Is a low cost regulator where I live. Kai Klaas |
