The Shop > Electronics & IC Programing
How to measure rippel of small DC/DC converter.
PekkaNF:
I have a silly question:
If I feed on one line cable a remote probe (1-2 metres away) have first linear regulator feeding an non isolated part of the circuit and then nearby (shielded) DC/DC converter providing an isolated power for the rest of circuit.
1: Any obivous problem feeding an linear regulator and DC/DC converter on same feed line?
2: have used before 317 type regulators, but there seems to be new low drop regulators available. Any suggestions to check data sheets and application notes on +/- 5 to 15 V range?
Thank you,
Pekka
eskoilola:
317 series regulators are actually power amplifiers. As such they suffer from same symptoms like limited bandwidth. It has difficulties in regulating very fast changes in input voltage or fast changes in load. In Your case some filtering would be a good idea. A small inductor and a good quality capacitor in the input side.
Further more, it would not be a bad idea to not let the DC/DC converter to yell into the feed line. Again, a small inductor and now maybe two good guality capacitors.
PekkaNF:
Thank you, that is very valuable. Used them on good old times, but had to make sure they had enenough voltage drop, bulk capacitors, some extra diodes (in automotive or such environment) and almost got comfortable with them.
I don't know the new kids on the block.
There are some new breed low drop stuff like LT1761, but I don't know how those behave with op.amps and converters.
eskoilola:
The LDO does not defy physics. The same rules apply - the to220 case WILL became hot unless cooled, the same voltage drop at a current still produces the same amount of heat.
I would suspect the new devices behave a tad better than the old (LM317 for example) with transients and stuff. They might also be less noisy and accurate.
The LDO is there just telling that the device is capable of working very near the input voltage (hence the Low Drop). The newer types also consume less current.
WeldingRod:
I suggest a tiny ac transformer. Speaking from experience, high frequency is hard to get rid of.
If you have some $$, call up AAK Corporation; quietest DC power supply I've ever found, and I was measuring 1 part in 15,000 signals on top of a 7000 out of 15,000 signal. Isolation is your friend!
Sent from my SAMSUNG-SM-G891A using Tapatalk
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