LDO bulk capacitance?

Hi everyone,

I admit that I am quite inexperienced in electronics.

I'm assembling a power supply for my DAC using this LDO in order to replace the original wall adapter that is dead (so the DAC already integrates its regulation).
Upstream I already use a 19v DC source (notebook power supply).

I need to understand if it is suitable to be used as is or if it is necessary to add some bulk capacitance to the output.

These are the already built-in SMD components:
X2 LT3045EMSE
X2 Cap Tant Solid 26uF 25V C CASE 10%
X4 Cap Ceramic 10uF 25V X7R 10%
X2 Cap Ceramic 4.7uF 25V X7R 10%
X2 Res Thick Film 0603 1% 0.1W

The doubt came to me because the same manufacturer sells a more ready-to-use version where you can see two additional capacitors.

If anyone could point me in the right direction, I thank you in advance.
 

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Disabled Account
Joined 2002
Hi, you won't need added bulk caps but you would need a transformer, rectifier bridge and filter cap (value dependent on drawn current or 4700 µF/A for LDO regs). This assuming the original PSU was a SMPS. You will need a way to transform 115V AC mains voltage to a usable low voltage DC to the LDOVR product. It is therefor an incomplete solution it seems.

This product is a quite good all in one PSU that only needs the transformer:

https://www.ldovr.com/product-p/tps7a4700-spsu.htm

You did not mention desired DC voltage but you can use the same voltage AC as the desired DC output voltage or slightly higher i.e. a 6V transformer for 5V DC output. For higher output voltages one better uses AC = DC voltages so 9V transformer for 9V output etc. Starting from 12V onwards one can even use slightly lower AC voltages. I use an 11V transformer for 12V output with LDO regulators.

Choose a transformer with a current rating minimal about 1.5 x the actual drawn maximum current.
 
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Disabled Account
Joined 2002
Yes you forgot :) Please note that the 19V SMPS may be noisy and riddled with RF. Possibly you will need extra filtering to filter that out a much as possible as even the best regulators let that through.

A mains transformer with real mains switch may be safer and have cleaner voltage and it will not pollute mains voltage as much as an SMPS either. Energy consumption also will be 0 when switched off and there will be no risk of fire when you are not at home which are all very nice benefits. You are located in Japan which means you have access to wonderful top class R-Core transformers by Kitamura Kiden! http://kitamura-kiden.co.jp/product/rcore/

Whatever solution you choose, make sure it can handle the current as drawn by that DAC. LT3045 based PSUs have the drawback that their absolute maximum input voltage is close to the SMPS output voltage which may lead to issues when that SMPS overshoots at power on. TPS7A4700 won't have that issue.
 
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As Jean said above, reg will let the filth trough. You can use marks filter to filter out most nm noise, but you still have cm noise. So best way is to use transformer and bridge, to supply dc to that regulator.

Yes, you need vin to be higher than vout. In ldo regulators, it doesn't have to be a much higher difference, but it still must be there. The higher vin the more heat.
 
Disabled Account
Joined 2002
1. You will only know for sure by measuring. Not by assumption. However the vast majority of consumer grade SMPS is not clean. They are cheap.

2. No linear regulator can work with 15V at the input to produce 15V output voltage.

Choosing SMPS for low power audio applications is like cutting your finger deliberately only to be able to stick a nice band aid (the filter) on the wound but the band aid won’t heal the wound.

It is more efficient to not cut your finger.
 
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Disabled Account
Joined 2002
Please measure the voltage under load as it might be too tight. Let’s say it puts out 13V at 0.25A. That will be slightly over 15V with an assumed ideal rectifier and then there are the (bummer) real life diodes voltage drop and ripple voltage.

No go I think. 12V output is possible. Schottky rectifiers and 4700 uF for 0.25 to 1 Ampère current. For a quality LPS you can use the stuff as pictured with a 15V R-Core transformer. A 2 x 7V (in series) will be better as 15 x 1.41 = 21V. The art is to have headroom and little loss to heat at the same time.
 
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