Questions tagged [linear-regulator]

A linear voltage or current regulator provides a continuous non-pulsed supply of current or voltage. It may be fixed or adjustable, and can be put under control by a CPU/MPU. In spite of sometimes low efficiency they are popular because they provide clean noise-free DC current or voltage, as opposed to switching supplies that can be very efficient with power regulation but induce much RF noise into the outputs which need extra parts to filter out.

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46 views

USB cable mod to use an external PSU [closed]

I have an external sound card connected via USB to my computer, and I recently tried to switch the computer's power-over-usb with an external (linear) power supply. The USB cable modification process ...
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2k views

Can a 1.8V linear regulator be avoided with 5V power and 3.3V?

This a theoretical question, I am happy with my current design, no intentions to try this yet. Background: Some PCB that has requirements of 5V, 3.3V, and 1.8V. The 5V is the supply from some standard ...
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84 views

How to properly model an linear power supply with LDO in LTspice?

I've build the following linear power supply: Before building it I tried to model it in LTspice. I couldn't find an LTspice model of L4941BV LDO (datasheet [PDF]) or a suitable replacement. Thus I ...
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84 views

How to design a discrete linear regulator with an opamp and an N-channel MOSFET?

So as far as I understand, the basic idea of a linear regulator is to use a series-pass element along with an opamp with negative feedback to stabilize the output. This is what I usually see as an ...
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93 views

Lithium Battery Charger using LM317

I have come across the following circuit in a datasheet for a battery charger: I have also seen a similar use of the charging circuit for use as a lithium battery charger, e.g http://shdesigns.org/...
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Overheating Linear Voltage Regulator In Lexicon Omega Audio Interface. Can I Swap With Reduced Amperage To Avoid Heat Probs?

I have a Lexicon Omega USB Audio Interface that's overheating. Already tried several heatsinks, including the biggest one I could get (6"Hx2.5"Wx.5"D) with optimized cross-cut vertical fins, mica ...
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How independent is the output voltage from the load resistor in this linear regulator?

Consider the circuit below: So we know that the op-amp will try to keep \$V_{+}\$ equal to \$V_{-}\$ (Inverting and non-inverting voltages of the op-amp) . Knowing this we can calculate the output ...
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LM7805 Voltage Regulator stops working when input voltage increases

I have the following circuit: simulate this circuit – Schematic created using CircuitLab I designed the PCB, had it printed and now I am testing it. When I power it up the following happens: ...
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59 views

Using a resistor to help regulator heat dissipation

I designed a circuit that consumes about 0.7 to 0.9 amperes depending on the state of its components. I use a 7805 regulator to feed the circuit with 5V and the regulator is connected to a 12V ...
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957 views

Voltage regulator datasheet does not specify input voltage

I am working with the TL783. I have 2 connected in series. The input to the first is 24V. The first configured to output 5.5V (R1 = 240, R2 = 820), the second configured to output 3.3V (R1 = 240, R2 ...
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Linear voltage regulator for LiPo and 3.3V@200ma ESP8266 - most juice

I am looking for a linear regulator that would follow these rules: input voltage from 3.3 - 4.2. (18650 battery or x3 AAA batteries) output voltage 3.3V @ 200 mA max. (for ESP8266). small footprint - ...
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4940v5 drop-in replacement for LM7805?

I am a novice who purchased several TO-220 L4940v5 chips thinking they were drop-in replacements for the inefficient TO-220 7805s that I've been using. But not a single one seems to work. No heat, ...
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What is the orientation of the pins in this drawing of an L4940V5 TO-220?

I am a novice trying to build a circuit using a L4904v5 voltage regulator. The datasheet has the following images: This 2D pinout drawing gives me few clues about which side I am viewing it from. I ...
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Understanding LDO Dropout

Disclaimer: Super newbie and first time poster here. The MCP1700 LDO regulator datasheet states on p3 that the Droptout voltage is 350mV for Vout > 2.5V @ I=250mA. I thought great I can power my ...
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Linear Voltage Regulator Maximum Input Current

I am trying to understand why the maximum rated input current is not listed as a parameter on linear voltage regulators. For example, the LM1117 lists nowhere on the datasheet the maximum input ...
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Powering Evaluation Board, Voltage Regulator Fizzles Out

I'm trying to power a FPGA evaluation board using a 5V linear voltage regulator. I supply the 5V through the USB connector as shown: (this goes to the microUSB on the board) For a basic test, I power ...
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What is the difference between a negative linear regulator and a positive one?

I am looking for a voltage regulator Vin = 5 V, Vout = 3.3 V, Iout = 400 mA. In my search I found negative linear regulators as well as positive ones. What is the difference and why ...
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60 views

How to protect/enhance an LDO so that it can sink current in the event of an external wiring fault?

Background I'm designing a signal acquisition board and one of its parts has several differential op-amps which are not very good from PSRR standpoint. So they need a very clean power supply, and ...
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77 views

Setting Rds(Ron) for PMOS for LDO

I am modeling LDO using ZXCL280 Datasheet. By understanding datasheet dropout voltage of the PMOS is seen as 1.46Ω(From page 5 ...
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129 views

Potential issue with voltage regulator on PCB: output voltage lower than expected

Background I've designed a simple PCB that, among other things, takes 12V as input, outputs a 12V to an Arduino Mega 12V input, and then—through a linear voltage regulator, and at least in theory—...
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159 views

IC linear voltage regulator with NPN transistor

I want to build this circuit using an NPN transistor instead of PNP: I don't know what changes I must make to this circuit. I built the same circuit but using NPN transistors. The current was far ...
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How to identify V-in V-out pins on Lineage Regulator?

I botched a soldering job and burned off the V-In pin of a micro FPV camera circuit. Luckily, I identified a lineage regulator next to it, which I see has a V-in pin from schematics of similar lineage ...
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Is a Synchronous Step-Down Converter powered from industrial 24v a good choice to power a 3.3 volt MCU and sensor ic?

I am building a sensor that will be powered from a 24v industrial power supply. The board will contain a 3.3 Volt MCU and sensor IC. Is it a good idea to use a synchronous step-down converter and just ...
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Voltage drop across power supply rail

I have multiple PCBs which are communicating via CAN and are supplied by two power sources (5V and 24V). After the first field test we noticed a considerable voltage drop at the power supply between ...
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LDO Voltage Regulator - Will there be an issue

I am working on a design that utilizes a LDO Fixed Voltage Regulator. The voltage in is 24V and expected voltage out is 3.3V. I know the part is spec'd for 24V (Vin-max) and output of 3.3V, but should ...
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LT3015 not regulating

I designed a simple circuit around LT3080 (positive linear regulator) and LT3015 (negative linear regulator). LT3015 datasheet I'm feeding them with +19V and -19V (input bypass caps not show) the ...
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Are all linear regulators bad at filtering input ripple? (or really as bad as Dave suggests)?

Background In EEVBlog #1116, Dave discusses a method to remove power supply ripple, and goes on to show (see 5:17 to 6:15) that you cannot count on linear regulators to remove your input ripple. He ...
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AC to DC power supply questions

I have built the circuit in the diagram below with a couple of minor changes. I desire 3 DC outputs - +12, -12, and +5 volts. So, the changes I made is to use an MC7812BTG for the +12 and an MC7912BTG ...
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5V LDO blowing up only when testing current draw

I have a circuit to power some 5-volt logic from a +24VDC source. It has some basic reverse-polarity protection and uses a TI 5VDC LDO. It all works great during normal operation however, when I use ...
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139 views

Best way to drop 10volts at 0.25A with linear regulator?

What would be a minimalistic circuit design to convert 14V to 3.3V at 0.25A with a linear regulator? I'm thinking about two linear regulators. I've tried LM7805(14V-5V) to LD1117(5V-3.3V.) LM7805 ...
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72 views

Positive and negative rail for op amp circuit

I need a positive and negative rail to power an op amp Since it's an op amp for a voltage reference, would using a circuit like this one be enough? Input voltage is unregulated 37 volts, with 4.7k ...
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205 views

How to wire several 78XX series regulators?

I have a 30V power source and I need to get several different voltages from it using linear regulator. 24V for op amps, 12V for relays and 5V for MCU. They all going to be installed on a heatsink. If ...
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68 views

Why Does the Input Voltage Drop When a Linear Regulator is Added as Load

Why does adding a linear regulator to this circuit cause the input voltage (V_c) to drop? The 9V input coming in is regulated. The voltage measured at the branch between D5 and R22 is ~8.7 V, so it ...
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277 views

Discrete linear voltage regulator

I am trying to make a discrete component linear power supply. This schematic seemingly works but it doesn't work when I build it on my breadboard. I am taking 110 volts through a transformer down to ...
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Controlling high voltage pulsed load

I have designed a power supply that has two outputs, one at -3kV (200mA) and one at -6kV (10mA). A new design challenge has arisen that includes the need to pulse both of the outputs from nominal load ...
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LM338 regulator resistor power rating

How do I calculate the power rating of the two 100 milliohm resistors in this circuit?
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What are the disadvantages of using a Zener diode over a linear voltage regulator?

I wonder why a Zener diode is worse than linear voltage regulator. Some of the posts online mentioned that because of the power dissipating problem. Zener diodes keep consuming a large amount of ...
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Driving 34 White LEDs in Series with Linear CC Source with 110V Mains

I have 102 White LEDs in total and I want to drive them from the 110V rectified Mains in 34S 3P configuration. Here's the graph about the LEDs (Red Line). I want to pass only about 50mA ...
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124 views

Linear power supply using LM338

I'm trying to design a linear power supply to provide 32V and up to 10 amps from a 50V source. Is this the correct way of using multiple LM338 regulators to achieve this?
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How do I tell if a voltage regulator is enough to supply a larger board?

So I'm currently designing a PCB that's fairly large by my standards (10"x5"). It's a 4-layer board with internal GND and 5V layers. I'm currently using a linear regulator (LM340SX) to provide the 5 ...
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Trying to get 2 Amps out of 3 Amp Regulator (MIC29302WU)

I am trying to get 5V,2A out of the MIC29302WU (TO-263 package) with an input voltage of 12V. The voltage drops to around 2.2V when trying to supply even 1.3A. Blowing canned air over the regulator ...
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86 views

Load current for LM317 [closed]

simulate this circuit – Schematic created using CircuitLab LM317 requires 10mA load to maintain regulation. the simplest option is to add a resistor, with a 10 ohm resistor as a load I get 16mA ...
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114 views

Controling LM317 digitally

simulate this circuit – Schematic created using CircuitLab I used OA1 as feedback for adjust pin and OA2 as a buffer, there's a 10 mA load at the output to meet the minimum load requirement of ...
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Linear regulator doesn't keep the right voltage when connected to ESP8266

I am trying to use a MCP1700-3302E LDO to regulate voltage from single-cell LiPo battery to my ESP8266 (Wemos D1 package). I intend to use the LiPo down to 3.5V, and since ESP8266 requires 3.3V, that ...
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273 views

Polarities of high current bypass, and short circuit protection, transistors on LM7912 - NPN or PNP?

With reference to Olin's answer to Connecting Voltage Regulators 7812 in Parallel for High Current, and likewise the examples from the Fairchild, TI and ST datasheets, a PNP transistor is used (i.e. ...
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305 views

Combining switching and linear regulators

If we have a 12V DC input voltage and we drop that voltage using a switching regulator (LM2596) to 9V and then use a linear regulator (7805) to drop 9V to 5V, what is the output voltage going to look ...
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46 views

ADXL354 Power Sequencing Sources and LDO's

The ADXL354 with Analog Outputs include three power pins: Analog Power Source V1P8ANA, Digital Power Source V1P8DIG and Logic ...
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1answer
157 views

Can someone explain the purpose of R53 in this old linear power supply circuit

This is an old linear power supply schematic. The 78GU1C is a four pin adjustable regulator. It adjusts its output to keep its sense pin, pin 1, at 5V. In this circuit, since there isn't a divider,...
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110 views

Adjustable LDO feedback resistor values

I'm designing a circuit using an LDO voltage regulator; specifically the LD39130SPUR from ST. This variant of the part allows for an adjustable output voltage via a potential divider as seen on page 8 ...
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186 views

LDO Heating Issue

I am working on a PCB project and having a problem with the linear regulator IC. I want to be able to maintain a relatively constant temperature for the heating element. The whole system is ...

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