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Questions tagged [7805]

7805 Voltage Regulator IC is a member of 78xx series of fixed linear voltage regulator ICs.

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25
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7answers
13k views

Optimize heat sink design - connect cooling pad on PCB backside by vias

In one of my current projects I'm using an MC7805 in a D2PAK package to generate my logic supply of 5 V from an available 24 VDC supply. The current required by the circuit is 250 mA. ...
23
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3answers
18k views

Why is there always a capacitor on input and output of a voltage regulator?

Looking at the datasheet I can see that the voltage regulators are not just a zenner diode inside, they are complex devices. I have noticed that there is always a capacitor at the input and another ...
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7answers
21k views

Can I use two 7805 ICs in parallel to get double current capacity?

I use a 7805 for a project where the circuit needs a higher current (~2.8 A) at 5 V. So I assume that if I use both ICs in parallel I can increase the maximum current capacity. Would it work?...
6
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3answers
4k views

L7805 destroyed - why?

I used a L7805 to power a Raspberry PI and it worked for about 10 seconds then started to smoke and die. L7805 is rated for 1.5A and 35V DC input. Power supply was 24V DC (was actually two plugin 12V ...
6
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5answers
3k views

What is the purpose of the 7805 input capacitor?

Most 7805 datasheets specify an input capacitor of 0.33uF or so. This one (the LM340 http://www.ti.com/lit/ds/symlink/lm340-n.pdf) at least specifies that the cap is only required if the regulator is "...
5
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3answers
2k views

Can a 7805 ever oscillate?

I see many references to input and output caps helping with "stability" and some outright references to preventing oscillation in both answers on this site, and even in some data sheets. I also have ...
5
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6answers
2k views

How to place a 7805 voltage regulator on a breadboard?

I have this breadboard and I have started experimenting with pic micros. In doing so I have needed a 5 volt power supply. I have seen several tutorials for wiring up 5 volt regulator circuits on a ...
5
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1answer
453 views

7805 sense resistors

In this answer, there is a schematic showing the internals of a 7805 voltage regulator, reproduced below: First of all, what is the sense pin in the first place? Every 7805 I've ever seen had three ...
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5answers
10k views

Selecting input voltage for 7805

I generally use switching 12V power supplies for my circuits since they are so common, but I understand the 7805 can take a lower input voltage. If I gave the 7805 a lower input voltage (i.e. 9V), I ...
4
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2answers
1k views

2N2222 experiment is indicating incorrect gains

Okay, so I put a 20kΩ resistor between a 5V supply and the base of a 2N2222 with the collector connected directly to the 5V rail and emitter to ground. What I'd expect is that, roughly, 220μA (i.e. (...
4
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4answers
1k views

Reducing voltage drop over 7805 regulator?

I have several projects (clocks) that require 12V and 5V supply. The 5V is for TTL ICs and the 12V powers a SMPS(Switching Mode Power Supply) to give HV(High Voltage) for a tube. The 12V pulls less ...
4
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1answer
637 views

Using two voltage regulators (780x) in series to prevent heat sink

(updated due to remark of ChrisStratton). I am wondering if it is a good idea to use two regulators in series. What I want: using 2 12V Nema17 motors (using 12V, 1.7A each). Using a microcontroller ...
4
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2answers
2k views

LM7805 followed by LD1117-3.3

The LM7805 datasheet recommends a 0.33uF cap on the input and a 0.1uF cap on the output. The LD1117-3.3 datasheet recommends a 0.1uF cap on the input and a 10uF cap on the output. I am building a ...
3
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2answers
1k views

Simple electrical circuit won't work

Simple NPN switching circuit to open a relay circuit, first NPN switching part didn't want to work (3rd PCB and endless times of trying). Circuit wizard diagrams, I split its first part to figure out ...
3
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3answers
4k views

Selecting the correct input/output capacitors for a 7805

So I've got a 7805 Regulator and I've been looking it up and each website says different info. I am using an input of 12V DC 1A Wall Adapter as an input supply. www.adafruit.com Says This ...
3
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3answers
6k views

Powering a Raspberry Pi from 12 V DC

I new to electronic engineering and am trying to learn electronic engineering by creating little projects. I have a few questions about powering my Raspberry Pi (5 V DC @1000 mA) from a 12&...
3
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1answer
1k views

Servomotor takes too much power so the µController (ATMEGA328P-PU) resets all the time

I have got the following circuit diagram. For a little explanation. When the button is pressed the µC is powered for about 10 sec. The µC contains code that moves the servo. When the servo is ...
3
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1answer
317 views

Choosing bypass capacitors for successive linear regulators

Background: I am reviewing my prototype PCB to iron out previous issues. The PCB is a Bluetooth data capture unit for liquid levels and flow. I am a software programmer by trade and I have some ...
2
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4answers
338 views

Is there an adapter for a TO-220 part to go into a TO-3

We have an old board that we do not want to redesign because it is near end of life. However, there is a TO-3 5V regulator that we can not source and when I do find it, it is for $13. I am wondering ...
2
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3answers
212 views

Capacitors for 7805CV?

I have some questions about using capacitors with an L7805CV According to the datasheet, on page 4, it shows I need: C1 = 0.33 uF C0 = 0.1 uF I bought a few sets some time ago with 'common' values ...
2
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2answers
5k views

Capacitor values for use with 78xx voltage regulators

I want to get the output: 5V - 25mA from 24VDC-0.75A with IC 7805. So what should be the value of C1 and C0? I need a formula for my report. thanks in advance
2
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1answer
862 views

LM7805 voltage drop when attach load

I've designed a circuit that I've already had tested it on breadboard and it has worked fine. When I did it on a PCB a new issue has appeared. The voltage regulator (I'm currently using a 7805) gives ...
2
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0answers
216 views

What is the purpose of the 7805 output capacitor?

How does a cap on a regulator output improve transient response? Is this cap not more appropriately drawn next to the load where it is not being defeated by intervening trace inductance? Or does this ...
1
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3answers
2k views

Can a DC regulator reduce/step down DC voltage?

I have studied that regulators like 7805 are used to remove the ripples present in the DC power supplies. But while searching for information about 7805, I came across the circuit below. The circuit ...
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3answers
230 views

H-bridge with 7815 regulator

Could anyone explain to me why my 7815 regulator gets hot and eventually blows up ??
1
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1answer
2k views

5v power supply using 7805

I want to create a 5v power supply design to provide power to my PIC18F4550, for that I am using 7805 so it will give the required 5v as output. I searched online and this is the diagram I found:- It ...
1
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2answers
5k views

How to measure AC and DC with oscilloscope

I'm a newbie with the oscilloscope. I have a digital RIGOL with two probes. I'm testing a simple 12V AC to 5V DC converter. I'm trying to measure the effect of the 7805 on the DC signal in output ...
1
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2answers
477 views

Positive and Negative Voltage Regualtors

I was wondering whether I could use a negative voltage regulator, specifically a 7905, as a drop-in replacement for a positive one, 7805. On closer inspection of the datasheet, I realized that pin 1 ...
1
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1answer
3k views

Is this an appropriate way to test a 7805?

Trying to check some 7805 voltage regulators. I do not have a DC power supply and do not want to test with the circuit hooked up to mains. That leaves me and my multi-meter. http://www.androiderode....
1
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1answer
27k views

How to unhide hidden pins in proteus?

Recently I was designing a PCB for my project using 89c51. I am using a 12V battery to run motor and 7805 to give 5V to 89c51. When going to ARES for PCB designing I realised the VCC pin of 89c51 is ...
1
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1answer
98 views

Current-limit circuit for 78XX voltage regulators

I need to find the value of Rsc and R1 in the following circuit: In this circuit, Q1 is the high-current pass transistor. Its emitter-to-base resistor has been chosen to turn it on at a given load ...
1
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1answer
144 views

3 terminal regulator max input voltage with zener at adjust pin?

Quick question: If I stick a zener at the adjust pin of a 3 terminal linear voltage regulator, the allowable maximum input voltage will also increase by the breakdown voltage of the zener used... ...
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2answers
590 views

Connecting the linear regulator directly to AC line

There are several out of the shelf solutions: LR8 from Microchip (formaly known as Supertex product) and NCP785 from ON-Semi. The last one is able to handle up to 700 volts at the input which is ...
1
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1answer
3k views

7805 for 4-20mA current injector

I'm trying to setup a low cost current injector for testing certain I/O modules. I found a rather simple design for a current source using 7805. simulate this circuit – Schematic created using ...
1
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1answer
59 views

Fluctuations in 7805 Regulator IC Output

I built an Arduino using ATmega328 on perfboard. To power it, I used an 8V adopter with a 7805 IC. But the ATmega328 IC started to reset randomly. After some efforts I figured out that the problem was ...
1
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1answer
36 views

Is it possible to use Ultrasonic sensor HC-SR04 in continuous power-on mode

I will be using Ultrasonic sensor HC-SR04 in water level measurement. I will be triggering the US sensor and getting back the time-pulse from it at very slow rate maybe once every minute. I want to ...
1
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1answer
244 views

Atmega328P - PU Not Working Properly (Instability, goes to sleep mode after some usage)

I have successfully designed & tested a circuit using arduino uno for controlling a dc motor (MAX 50A,12V,SHORT-DUTY) By using a relay module and current sensor (configuration given in schematic). ...
0
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2answers
2k views

Why 7805 regulator gives output 6 volt?

I am using 7805 and 7815 for the voltage 5 V and 15 V respectively. I provide 24 V to 7815 it is giveinng me output voltage 18.5 V instead of 15 V. According to 18.5 V to input to 7805, its output is ...
0
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5answers
164 views

Is it possible to use 7805 regulator without capacitors at its input and output pins?

I have to drive a magnetic buzzer whose current is 50mA and max. voltage is 6V. I will use 7805 regulator to drive it as my supply voltage is variable 9V to 24V DC. There will be another small load ...
0
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2answers
5k views

how to fix Heating issue of 7805?

i am using LM7805 whose output voltage 5V and Output Current 1A i have used this to feed 5V supply for my application Circuit and my application circuit draw 125mA current , even tho 125mA current ...
0
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3answers
134 views

will my linear regulator overheat?

I am making a new design which I use a 4S 18650 batteries with total voltage of 14.8V in my design I need to have 9V and 5V using 7809 and 7805 regulators are these regulators going to overheat ? ...
0
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2answers
726 views

Power supply fluctuations. Bypass capacitor needed?

I am powering up a 5V device using a 12v DC 1A SMPS power supply. The 12V supply is connected to the 5V device through a 7805 voltage regulator. The device draws about 30mA when idle, but when it ...
0
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2answers
493 views

L7805CV won't go higher than 7.5

I am trying to use a STMicroelectronics L7805CV to increase voltage from 7.5v to about 12v, but I can't get it work. I've placed 470 ohm resistors between out and common and between common and ground, ...
0
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1answer
242 views

Why is this circuit letting the smoke out?

Using this circuit as a proof of concept to run a 12v motor off a 12v wall wart and ultimately use the 5v from the 7805 to power a Particle Photon through Vin pin. This circuit is letting the smoke ...
0
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2answers
64 views

Going under specs for a linear regulator?

I have a Microchip PIC board (18F46K22) which has a VIN pin to connect to a power source (7vdc + supply). What happen if I feed 3.3V to the VIN which goes through the 5V linear regulator (ST 78M05)? ...
0
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2answers
152 views

Why peak output current is greater than short circuit output current in 7805 voltage regulator?

This is the datasheet of 7805 voltage regulator produced by "Continental Device India Limited". Question: Why is the peak output current greater than short circuit output current? Shouldn't the ...
0
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3answers
2k views

How to limit current for voltage regulator/decrease power dissipation?

I need to power a 5V device that needs more or less 1.2A in order to work correctly. I'm using a 13.8V power source with two diodes in series (1N4007) to limit the voltage to roughly 12V. I tried ...
0
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2answers
452 views

Does the MC7805CT-BP need capacitors?

As far as I know, you have to put capacitors on most voltage regulators. However, the data sheet for this one specifically says "No external components required" and furthermore goes on to state "...
0
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1answer
3k views

Can I use a 7805 as a current regulator?

Can I use 7805 as current regulator? My input is 12-14 V DC (battery) and I require output 5V and 500mA or adjustable. My background is CS so unaware of these ICs. I have searched LM317 and LM338 but ...
0
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2answers
1k views

LM78H05K How to use

I have bought the LM78H05K 5 V voltage regulator , for the 5v output. My input voltage is 17 V DC. but unfortunately this component is in different shape. I have uploaded the image of the module. I ...