The best bang for the buck 5V LDO regulator

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#5
peranders said:
What is your application?
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It is for a Kali reclocker and Piano 2.1 DAC for a Raspberry Pi . I assume this already has internal regs but I want to get rid of the noisy outboard switchmode . I am aware of some of the best sepc'd reg chips have impossibly small or difficult to use packages . I would simply like to find a 3 pin TO220 type reg with superior specs to the LT108x type devices at reasonable cost 🙂

316a
 
#14
In principle LDO's will be able to effectively reduce supply ripple up until hundreds of kHz, some models will work even above 1MHz. Just look at the PSRR curves for a particular model. This is normally sufficient to get rid of converter switching frequency related ripple. The problem is that most DC-DC converters will emit short pulses of "ringing" in hundreds of MHz range which no LDO can stop. In this case a Pi filter using ferrite bead and a couple of suitable ceramic capacitors will help to reduce this HF noise before it enters the LDO.

Regards,
Oleg
 
#15
forestsgump said:
Yes this would work, low enough ripple noise and rather affordable!
Except only max. 15v DC input, I need something wide that can accept 32V and gives 5V @ 0.2A nominal.
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Well… there is "the obvious" I guess. Two of these in series, to drop 20 volts: 1N5347BG ON Semiconductor | Mouser

Cost $0.47 ea. For a buck, you can kill 20 volts. 10 watts (½ amp) of series dissipation. More than enough for your needs.

GoatGuy
 
#16
GoatGuy said:
Well… there is "the obvious" I guess. Two of these in series, to drop 20 volts: 1N5347BG ON Semiconductor | Mouser

Cost $0.47 ea. For a buck, you can kill 20 volts. 10 watts (½ amp) of series dissipation. More than enough for your needs.

GoatGuy
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Thks, it is cheap & quick way to get to 12V, follow-by linear regulator to get low noise 5v. I do have to consider if waste 5-10W and the heat coming out.
 
#17
OlegSh said:
In principle LDO's will be able to effectively reduce supply ripple up until hundreds of kHz, some models will work even above 1MHz. Just look at the PSRR curves for a particular model. This is normally sufficient to get rid of converter switching frequency related ripple. The problem is that most DC-DC converters will emit short pulses of "ringing" in hundreds of MHz range which no LDO can stop. In this case a Pi filter using ferrite bead and a couple of suitable ceramic capacitors will help to reduce this HF noise before it enters the LDO.

Regards,
Oleg
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Pardon my amateurish, how significant is DC-DC converters‘s MHz noise have an effect on SQ of DAC, say 192khz?
 
#18
Look at my measurements of the OPA1622 headamp powered by a DC-DC converter here. The problem is not only the ringing frequency itself but also the interval at which these ringing spikes are emitted, which is in hundreds of kHz range and can well interfere with the DAC. Also noise in MHz range can couple through the clock supply and the DAC supply itself since internal logic of the DAC runs at MHz frequencies. I am sure there are multiple ways the performance of the DAC can be affected by the switching noise but unfortunately I am not a big expert to discuss it in details.
 
#19
OlegSh said:
Look at my measurements of the OPA1622 headamp powered by a DC-DC converter here. The problem is not only the ringing frequency itself but also the interval at which these ringing spikes are emitted, which is in hundreds of kHz range and can well interfere with the DAC. Also noise in MHz range can couple through the clock supply and the DAC supply itself since internal logic of the DAC runs at MHz frequencies. I am sure there are multiple ways the performance of the DAC can be affected by the switching noise but unfortunately I am not a big expert to discuss it in details.
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Oh... then this discovery maybe could be concern China-made Class D amplifier bundled with SMPS, as these amplifiers usually has front-end Preamp supply by LDO running-off from SMPS.
 
#20
forestsgump said:
Thks, it is cheap & quick way to get to 12V, follow-by linear regulator to get low noise 5v. I do have to consider if waste 5–10W and the heat coming out.
Click to expand...

I thought you only needed 200 ma. remember P=IE so

P = IE = 200 ma × 20 V
P = 4,000 mW
P = 4 W

Is it really worth designing a fantastic contraption to overcome a veritable non-problem like this? Just asking. I, being older than any-two-millennials-combined, think not. Wasting 4 W is nothing.

GoatGuy
 
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