On 9/2/09, Richard <[email protected]> wrote: > > > > > On Sep 2, 6:31 pm, Sebastien Lelong <[email protected]> > wrote: > > > > Is L78L33ACZ an option ? TO-92 package, could be used instead of > > > TO-220. But > > > > only 100mA output. I don't know if electrical specs are compatible > > > too... > > > > > Sorry forgot, L78L33ACZ is no good specs, to high dropout voltage, > > > 1.7V is to critical > > > > What is dropout voltage ? Is it the voltage amount needed in addition the > > wanted one ? > > Minimum voltage drop over the component so deference between the > minimum voltage input (supply) and the voltage output > > > Ex: I want 3.3V. Dropout V is 1.7, so I need to power the regulator with > at > > least 3.3 + 1.7 = 5V ? > > Yes, you got it
Assuming the input voltage is only filtered, you can't measure the voltage dropout correct with a digital multimeter, because the multimeter measure the RMS in AC and a medium voltage in DC. The ripple of the input voltage is AC but the input voltage has also a major DC component. So that 1.7V should be measured between the bottom of the input ripple and output of the stabiliser voltage. That means much more than 1.7V measured on a DVM. For enlightement, a 20V DC voltage filtered with 10uF capacitor (value choosen just to understand)could have the bottom voltage ripple at 20V when the source current is zero (no ripple) and at 2V when the source current is say 100mA. That's why you need a scope if you wand to check an LDO with very low dropout (less than 0.5V) and the right computed filtering capacitor. Second problem, if you supply from USB, all noise from computer will be present in your board. Note the common LDO does not reject more than 10KHz. Does not hurt untill you'll have the ideea to interface a 24bit AD converter to your Jaluino. Vasile --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/jallib?hl=en -~----------~----~----~----~------~----~------~--~---
