37
votes
What is the difference between a linear regulator and an LDO
An LDO is a type of linear regulator.
All linear regulators have what's called a dropout voltage, a minimum input-to-output differential that they can't work without. The original linear regulators (...
- 38.5k
37
votes
Accepted
What is the difference between a linear regulator and an LDO
They key property of the LDO type linear regulators is the P-type pass transistor. This allows controlling the pass transistor with a voltage below the input voltage \$V_{in}\$ for all possible output ...
- 23.4k
35
votes
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What is the purpose of a 1 Ω resistor to ground in the output filter of a voltage regulator?
The first easy to use 'one component' regulators to be produced, like the 7805, were NPN follower based. This meant they had a high(ish) dropout voltage. The low output impedance, and the ...
- 174k
26
votes
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Are all linear regulators bad at filtering input ripple? (or really as bad as Dave suggests)?
In the case of the MCP1700, Dave is certainly correct.
Here's the ripple rejection versus frequency chart from the datasheet:
The datasheet itself claims 44dB of ripple rejection at 100Hz, which ...
- 73.5k
21
votes
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Capacitors with an LDO voltage regulator - how necessary is it?
The data sheet for the regulator suggests ... How important is this?
About as important as that your circuit work reliably.
Trying to second-guess datasheets is a bad idea. Unless the datasheet ...
- 315k
21
votes
Are all linear regulators bad at filtering input ripple? (or really as bad as Dave suggests)?
It doesn't entirely excuse the poor performance of the MCP1700, but I think you'll generally find that very low Iq regulators tend to have much poorer high-frequency PSRR.
You would not expect an op-...
19
votes
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Ferrite instead of LDO
Ferrite Beads and LDOs are typically solve two different kinds of noise problems, so very rarely will you be able to "replace" an LDO with only a Ferrite Bead.
LDO's ability to filter noise is ...
- 989
17
votes
LD1117v33 delivering 10 V instead of 3.3 V - what is wrong?
To be clear and to protect against changes to the question, here is your schematic:
There are a number of problems here, both with the schematic and the circuit:
The schematic is missing junction ...
- 315k
16
votes
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Efficiency of a voltage regulator
Let's say I have an LDO that create 5V at 2A with an input of 10V at 1A...
You have 10 W input, and 10 W output, therefore you have 100% efficiency.
...with an efficiency of 50%
This is a ...
- 134k
14
votes
Connecting GPIOs on two boards with independent power supplies
In situations like this, I like to use an optical coupler (example) in between the two systems. The systems will remain electrically isolated, so no current will flow between them in either direction. ...
- 1,128
13
votes
Are all linear regulators bad at filtering input ripple? (or really as bad as Dave suggests)?
My practice is to use a large enough capacitor before the LDO to handle high frequency ripple, with a small R or L before it if necessary, and rely on the LDO to remove the low frequency variations. ...
- 174k
13
votes
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The 3.3V Fixed Regulator was burned with 12V input
Your load is the problem. With 12 V input, you're dissipating \$(12-3.3)\ \mathrm{V} · 100\ \mathrm{mA} = 870\ \mathrm{mW}\$. For the DBV version, the datasheet lists an approximate Rthj-a of 212.1 °C/...
- 38.5k
12
votes
What is the difference between a linear regulator and an LDO
A low drop out regulator (LDO) is a linear regulator.
Linear regulators control the output voltage by adjusting the current through an output transistor.
In all linear regulators, there is a minimum ...
- 73.5k
12
votes
What happens if I accidentally ground the output of an LDO regulator?
You don't currently state your VIN voltage.
If your short V+ on your circuit, you're just connecting the 8.45K resistor to become a load across the regulator output.
The MAX6004 has a 4.096 V output ...
- 23.8k
11
votes
LD1117v33 delivering 10 V instead of 3.3 V - what is wrong?
You certainly need a capacitor at the output. From dataheet.
Stability
The circuit design used in the AMS1117 series requires the use of an output capacitor as part of the device frequency ...
- 6,443
11
votes
Are all linear regulators bad at filtering input ripple? (or really as bad as Dave suggests)?
This is cherry picking functionality of a particular part. An ideal LDO has infinite PSRR so what is the limiting factor on real LDOs that degrades performance at high frequencies?
I recommend you ...
- 4,729
11
votes
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Is this an acceptable way to create +/-5V from +/-12V?
No. What you're calling "-5 V" would actually be +5 volts with respect to the -12 volt rail, i.e. -7 volts. And it would only be able to source current into a load returned to a lower ...
- 38.5k
10
votes
Accepted
Is creating a voltage rail loop good or bad practice?
Having low impedance on the power rail is always a good thing. So multiple power paths aren't bad in general.
However a star-pattern or power plane can be better if emi is a concern.
Any ripple caused ...
- 904
10
votes
Is creating a voltage rail loop good or bad practice?
A related peripheral issue worth being aware of:
If you have analog measurement points on a board, whether internally sourced or from external sources, then at the signal levels usually dealt with by ...
- 152k
10
votes
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Low LDO output capacitance (stability)
LDOs are feedback systems, so their stability depends on open loop gain: output voltage -> error voltage on FB pin -> internal error amp -> pass device -> output voltage.
The classic ...
- 81.6k
10
votes
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Automotive Controller LDO Failures
Yes, transients are likely an issue. UA78L05AC has an absolute maximum 40V input rating. Many of the transients defined in ISO 7637-2 or ISO 16750-2 exceed this, at impedances and time scales that ...
- 45.6k
9
votes
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Replace AMS1117 5V-3.3V LDO on NodeMCU for LiPo with low quiescent current
You choice looks good to me, but only if your NodeMCU is going to spend most of its time sleeping. In that case I'd use a MCP1700 (quiescent current < 4 uA).
If it's going to spend a significant % ...
- 5,841
9
votes
Capacitors with an LDO voltage regulator - how necessary is it?
You should follow the recommendations in the datasheet. If you don't, you risk oscillation. The regulator starts to oscillate - the output goes up and down. When I've had it happen, the regulator ...
- 73.5k
9
votes
At what point should I switch between a resistor divider and a LDO?
It is never a good idea to power anything from a resistor divider. Any variation on the load will change the voltage, and your MCU will very likely vary its current consumption based on what it is ...
- 12.2k
9
votes
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How to reach ~50nA p-p current noise in ~200mA current source?
The main theme is: eliminate sources of 1/f as far as possible and limit bandwidth as desired. I suggest the following principal circuit (details added further down):
Low Noise Resistor
The main ...
- 23.4k
9
votes
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LM1117 LDO - Vout variability?
The problem is that you have, as you put it, no "capacitors or anything else connected".
There are two problems with that:
The LM1117, like most linear regulators, requires those capacitors ...
- 38.5k
9
votes
Accepted
Does the HT73xx LDO regulator series have reverse polarity protection?
What happens if I feed it -10 V instead of +10 V?
You will find this in the data sheet: -
Basically any input voltage more negative than -0.3 volts will potentially cause it damage and, in my ...
- 473k
9
votes
Connecting GPIOs on two boards with independent power supplies
Generally speaking, as long as both boards are powered up and their power supplies are within specification for the FPGAs (e.g., ±5% or ±10%), connecting the GPIO pins directly to each other should be ...
- 178k
8
votes
Difference Between RMS noise and PSRR in an LDO
The noise is internal to the LDO and is always on the output whether you power it directly from an SMPS, a battery, or the most perfect noiseless voltage source.
The PSRR is how well the LDO can stop ...
- 57.3k
8
votes
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3.3V regulator does nothing for first ~12 seconds after power-on, then outputs 5 volts
Short answer : The TPS78633 NR pin is incorrectly connected to 3.3V output, and it is causing the issue.
This overrides the internal Vref of 1.25V with the output voltage, and it tries to set the ...
- 172k
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