Electronics > Beginners
Voltage regulator recommendations
David Hess:
With those low current levels, I would use operational amplifiers. Instead of a reference, I might even have them track the positive or negative 15 volt supply voltage.
If low AC output impedance is required or if they have to drive ceramic decoupling capacitors, it may be necessary to frequency compensate them to handle a capacitve load. One counter intuitive way to do this is to add like a 10 to 100 microfarad electrolytic capacitor directly from their outputs to ground but this should be tested for the operational amplifier selected. Lower power operational amplifiers are more picky about driving output capacitance although some parts are designed to have unlimited capacitive load driving capability and they would be ideal in an application like this.
newbie666:
Thanks Davis,
I think I'll go with this solution. I'll use a reference rather than track power supply rails though.
Do you have any suggestions for the opamps that would be good at driving capacitive load?
I've started googling opamps driving capacitive load and I found this nice writeup with scope screenshots and all:
http://www.analog.com/en/analog-dialogue/articles/techniques-to-avoid-instability-capacitive-loading.html
Posting here in case somebody else has the same problem.
I found this part from TI: LM8272, however it's pricey at over 3 bucks in single quantities.
james_s:
Try something cheap to begin with, if that doesn't work then look toward fancier parts. Something like the TL084 would probably work.
David Hess:
If you compensate it right, then any operational amplifier can be used. Linear Technology has the LT1351/LT1352/LT1353 which might be ideal but they are not cheap. I did a search for TI parts and did not find any suitable ones. The three alternatives using frequency compensation are:
1. Swamp the output with like a 10 to 100 microfarad aluminum or tantalum electrolytic to ground resulting in dominant pole compensation. This can provide about the best performance but it should be tested. Do not use a polymer electrolytic (or ceramic or film) part because low ESR will defeat the purpose of using this method.
2. Use the capacitive load driving circuit shown in the last example here. I have actually had better results with method 1 above. It is not that this does not work but it has a mid-band rise in impedance which may be a problem with some loads.
3. Use an operational amplifier which provides external compensation so its capacitive load driving capability can be increased and then use 1 above.
There are some power buffers like the LT1010 which can also be used but an operational amplifier is more economical and better at low power.
Navigation
[0] Message Index
[*] Previous page
Go to full version