Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [ldo]

A Low Drop-Out or LDO regulator is a DC linear voltage regulator which can operate with a very small input–output differential voltage.

541 questions
9
votes
4 answers

Why do LDO regulators have so big a voltage drop?

Why do LDO linear regulators not use MOSFETs as the main component to be able to have minimal dropout=0 (well, depending on current, must be still a few mV)? Or can one expect to build a 0-dropout regulator based on a MOSFET and an opamp?
BarsMonster
  • 3,327
  • 5
  • 46
  • 80
7
votes
2 answers

Is it safe to bypass an LDO by shorting its input and output?

I am making a programming adapter that will deliver 5V or 3,3V to the target board. I want to use a simple DIP switch to select voltage (I know that an SPDT is the canonical way). Is it safe to short the input and output of an LDO like LD1117.…
filo
  • 8,951
  • 1
  • 25
  • 46
7
votes
2 answers

Diodes in LDO schematic

Could someone please explain why are there two Schottky diodes in this schematic? And also why is the VOUT connected through one of them to VIN.
Herr Krum
  • 129
  • 1
  • 8
6
votes
1 answer

Meaning of LDO's dropout

I'm studying an LDO circuit consisting of a PMOS pass element. I cannot fully understand the meaning of dropout voltage. I thought this is the minimum V_SD to ensure that the PMOS operates in the saturation region. I had a hand calculation, with…
남창연
  • 81
  • 3
4
votes
0 answers

Low drop out regulator

For an LDO (Low drop-out regulator) I am having below two questions but couldnt find a good reference to answer them. What determines Bandwidth of an LDO? For e.g. for a change in load current what range of frequencies can be supported by an LDO to…
ritvik rathore
  • 339
  • 1
  • 9
3
votes
2 answers

Open ended LM2937-5 outputs 12V

The LDO, LM2937-5, with 12V input voltage and nothing connected to the output terminal, outputs 12 V (measuring using voltmeter). As soon as I connected 100 uF capacitor, it shows 5V. Datasheet clearly states that output capacitor is required, but…
Anonymous
  • 7,052
  • 1
  • 14
  • 45
3
votes
1 answer

What if I source 3.3V to the LDO(AMS1117-3.3) output pin?

We feed DC 5V into VCC_EXT_5V and then it outputs 3.3V to the 3V3 in the normal condition. The following is a part of the power circuit. My question is followed: How does it work if I connect the other 3.3V power source to the 3V3 leaving the…
Blue Cloud
  • 178
  • 1
  • 12
3
votes
2 answers

How to calculate this LDO regulator, and how to prevent it from oscillating?

I am further playing around this PMOS LDO circuit I designed and attempted to test and rate (the Edit 3 schematic, simplified by removing the protection circuit). After I dropped in a NJM4559 op amp in place of LM358 it started oscillating (previous…
Maxthon Chan
  • 2,873
  • 1
  • 16
  • 34
2
votes
3 answers

Can I use an LDO voltage regulator as current limiter?

Like this, connect the ADJ and Vout of an LDO directly. The principle of an LDO is to make Vout 1.25 V higher than ADJ. As they are connected, Vout can never be 1.25 V higher than ADJ, and the LDO internal resistance will be very low. Meanwhile, the…
seafood 2019
  • 23
  • 5
2
votes
2 answers

LDO input/output oscilation

Uploaded the load of TIA amplication circuits, there are four same ciruits. Some updates: I've made two layouts and one of them is much easier to have the osilation. I've designed and tested with LT3045 transferring 5V to 4.5V. There is a large…
FNJU
  • 43
  • 5
1
vote
0 answers

Split DC power supply review

Currently I am working on a AC (mains)->DC (split-rails) linear supply project. The intended use is for hobby purposes only. As I am not used to split supplies and AC/DC sections, I'd like to ask if there are any obvious errors in my schematic. The…
ElectronicsStudent
  • 3,489
  • 7
  • 20
1
vote
1 answer

Wrong voltage out of ST LE33: 1V instead of 3.3V

I got an ST LE33 and I am providing +5V between pin 2 and pin 3 as per specs. Checked with a multimeter. I am reading +1V between pin 1 and pin 2, without any load, no capacitors. If I put a 1MOhm resistor, the voltage drops a bit. I took a picture…
Paperino
  • 215
  • 1
  • 7
1
vote
2 answers

Vin-Vout Difference vs Dropout Voltage (on the LDL1117 regulator)

I have identified the LDL1117 (specifically the LDL1117S33R) to reduce a 4V DC voltage to 3.3V DC. The max current draw is 500mA. I had initially selected this part because I read the dropout voltage is 350 mV @ 1.2A. However on reading the…
ankGT
  • 57
  • 4
1
vote
2 answers

5V LDO replacement for multimeter

I have a 9V powered multimeter (Voltcraft VC165) where the 5V LDO is broken. When I apply 5V manually, the functions I checked so far work fine, so I'd like to repair it. The LDO is a SOT23-5 SMD part, the mark says "PAW", there is no logo…
mic
  • 996
  • 1
  • 6
  • 14
1
vote
0 answers

LP2950-50LPRE3 (TI) Vout unexpected

Background I'm working on application that I think the LP2950-50 would be appropriate for. I want to control a set of SSR 40 DAs from the GPIO pins of a raspberry pi. Empirically, I've found that 5V applied across Vin of the SSRs works best to…
Craig Niles
  • 11
  • 2
1
2 3