Questions tagged [7805]

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

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25
votes
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. ...
20
votes
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?...
23
votes
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 ...
5
votes
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 ...
6
votes
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
votes
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 ...
6
votes
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 ...
2
votes
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 ...
5
votes
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 ...
4
votes
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 ...
1
vote
2answers
476 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

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
vote
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 ...
0
votes
2answers
724 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
votes
2answers
140 views

Voltage regulator question

I have made a portable device charger with a 5 volt voltage regulator(7805-TO220 package),a 9 volt battery and a few capacitors.The problem is,when I connect the charger to a certain device(whose ...
0
votes
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
votes
1answer
663 views

Voltage regulator Current regulation

I want to understand the concept of current regulation in the circuit, In my research I came across the following link Boosting Regulator Current for IC 78xx by MJ2955 where in the circuit schematic ...