Skip to main content

Questions tagged [lm78xx]

LM78xx are a popular series of linear voltage regulators. To name a few 7805, 7809, 7810

Filter by
Sorted by
Tagged with
0 votes
2 answers
87 views

Dual power supply, AC to ±12V DC, based on LM7812 + LM7912

I'd like to build a power supply, based on the LM7812 and LM7912, that outputs both +12 V and -12 V. I found this circuit online: According to the datasheets, the LM7812 has a typical dropout voltage ...
bmatcuk's user avatar
  • 113
0 votes
4 answers
449 views

Why is the LM7812 getting hot in this circuit?

I have made this circuit. It works fine with normal Zener diode, however when I replaced it with the LM7812 it works fine but as time passes the regulator keeps getting very hot although the load is ...
Hazardous Voltage's user avatar
1 vote
1 answer
230 views

Make a switchable steady 5 V output circuit

I am looking to make a very accurate steady 5V power supply that can be switched on and off using the digital IO pins on an Arduino. I planned to use a 9V power supply connected to a 2N2222 transistor ...
R Doyle's user avatar
  • 13
3 votes
1 answer
113 views

What could have caused my power supply to fail?

I made a dual +/- 12 V power supply for synthesizer circuits using a schematic by Moritz Klein (image below). The input of the supply is from a 12 VAC transformer. After soldering the circuit on a ...
fatNinja_Cat's user avatar
0 votes
0 answers
41 views

In which option, the diode will make the lm78xx circuit safer

This image was taken from Fairchild's datasheet on lm78xx. I have already built a working example of it, but I am still thinking about adding some additional diode protection (D1, D2). Which option ...
pggu11's user avatar
  • 33
0 votes
2 answers
350 views

LM7805 decoupling capacitors

Would it be possible to replace these combinations of ceramic and electrolytic capacitors with just a pair of low-ESR 10 μF ceramics? Conversion from 12 V to 5 V, minimal consumption, only MAX485 ...
Erick.87's user avatar
0 votes
2 answers
179 views

A question about 78XX power supply design

I want to get 12V and 5V from a 24V power source. 12V drives a MOSFET H bridge and a cooling fan. 5V is for a microcontroller. I have already damaged a microcontroller due to a failed 7805 regulator. ...
shan's user avatar
  • 103
1 vote
2 answers
700 views

Applying 5V on output pin of LM7805 while the regulator is not powered

According to the Datasheet of LM7805 (section Application and Implementation), in some scenarios a protective diode (between IN and OUT pins) is needed to protect the regulator. Please take a look at ...
Osoian Marcel's user avatar
0 votes
2 answers
201 views

Help me understand the calculation of the current consummated by LM7805

Please help me understand how to calculate the current consummated by LM7805 during its work. Parameters: V(in) = 12V V(out) = 5V I(load) = 10mA (0.01A) The image ...
Osoian Marcel's user avatar
0 votes
4 answers
300 views

Can LM7805 take 30 V max as input if the load current doesn't exceed 50 mA?

Can I use a simple LM7805 for my beeper hobby circuit that monitors a 30 V battery? The load current doesn't exceed 50 mA. It seems the IC will dissipate (30-5)*50 mA = 1.25 W worst case. Will the IC ...
across's user avatar
  • 105
-3 votes
3 answers
508 views

Why does the LM7805 heat up? [duplicate]

I'm really not comfortable with things heating up, including this LM7805 integrated circuit wired below. Why does this mighty LM7805 heat up? Thank you for the help!
Shobeh's user avatar
  • 27
1 vote
3 answers
2k views

Transistor for increasing current output of linear voltage regulator

Based on a suggested circuit from the datasheet, supplied current of LM7805 voltage regulator can be increased. I can't source that BD536 PNP transistor or any equivalent listed on some websites. ...
Elementronics's user avatar
0 votes
2 answers
342 views

Can I somehow make the LM7805 work hand in hand with an N-channel MOSFET to get more current out of the regulator?

I've seen the circuit with the LM7805 being used hand in hand with a PNP to provide more current. My problem is the heat that comes with said configuration. Isn't there a way to make a linear ...
BELSmith's user avatar
  • 146
3 votes
3 answers
2k views

Which capacitors to use with voltage regulator IC such as 7805?

Many of the tutorials suggest to use a large smoothing capacitor (tens and even hundreds of uF) with a full wave rectifier but the datasheets of the voltage regulators and some tutorials suggest only ...
Asmat Ali's user avatar
  • 333
0 votes
0 answers
86 views

how to calculate C for lm7809?

I need to use a LM7809 to reduce 12-14V to 9V , the device is using 40mA at normal state when I search google for application circuit - I got all kind of valus for Cin , Cout. use this datasheet ...
Afik_Android's user avatar
3 votes
2 answers
611 views

Suggestions for dropping resistor on LM78 regulator

I’m trying to repair a magnetic stirplate (see http://staff.washington.edu/wbeaty/chem_stir.html). I found that in one part of the circuit it fails to deliver 12V. I’ve draw part of the circuit below: ...
Ted43's user avatar
  • 31
3 votes
1 answer
453 views

78L24 outputs high voltage >24v - Harman Kardon AVR 151

I'm trying to repair my broken Harman Kardon AVR151. Looking at the SMPS schematic, to my very limited knowledge I do not understand, The 78L24 is a high side 24V regulator. Why does the schematic ...
Jinantha Perera's user avatar
0 votes
2 answers
2k views

How to fix dc 12 led lights that burn out due to excess voltage or current

How to limit the output DC voltage to dc 12V if the input voltage is greater than DC 12v, and it outputs same voltage if voltage is below 12 V like 11.5 V or 10.5 V? Scenario: I have solar setup at ...
Adnan Katper's user avatar
0 votes
1 answer
372 views

Why does my LM7805CV output voltage drop at loads <= 150 mA?

According to this answer the LM7805 has no minimum load. The data sheet also indicates that the output voltage should remain between 4.8 and 5.2 V for output currents of between 5 mA and 1 A. I have ...
cjs's user avatar
  • 990
8 votes
5 answers
5k views

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 ...
mannok's user avatar
  • 491
1 vote
4 answers
193 views

Does placing additional capacitors in parallel with CJ7805 affect its performance?

I'm not sure if this is a stupid question, but I'd still prefer to ask than regret it later. I'm designing a PCB with the CJ7805 which, like the LM7805, can supply a steady 5 volts. In this case, it's ...
Espresso's user avatar
  • 199
0 votes
1 answer
187 views

Using series of LM 78XX for power supply

I'm new in electronics. I want provide 9V (VVD9) and 5V (VCC) for my electronic board including power mosfets (IRF 3205), high power LED (14V-3.5A), micro-controller (at-mega16), and etc. I use this ...
Babak.Abad's user avatar
1 vote
3 answers
2k views

Zener Diode vs LM78XX

To get, say 5VDC, from the AC mains, after stepping down the high AC voltage using a transformer, we have to rectify it and regulate the output DC voltage. As I have seen, there seems to be two ...
Bhuvnesh's user avatar
  • 612
3 votes
1 answer
8k views

How much power does LM7805 dissipate?

I'm using an LM7805 in voltage regulator mode. Vin is 15V Vout is 5V (regulated) The attached load draws 200mA How to calculate how much power the LM7805 would dissipate in this setup (and whether ...
rustyx's user avatar
  • 193
8 votes
1 answer
5k views

Series pass transistor, LM7812

I am making a 12 volt regulator for a solar panel to power an audio amplifier. I already have a switching regulator for most application but it is very noisy for amplifier even with a lot of filtering....
Hamza Khan's user avatar
0 votes
1 answer
109 views

Connector acting as ground?

I am building a power supply using LM78×× voltage regulators. The circuit works as expected with no load but when I connect the circuit to external connectors, LM7812 on circuit starts getting very ...
Rutuparn_Pawar's user avatar
-3 votes
1 answer
244 views

Lm7812 circuit help

In circuit to get a steady 12v DC I don't understand the use of the capacitors. Can anyone help me?
Nobody's user avatar
  • 1
3 votes
1 answer
534 views

LM7805 Voltage Drop too big

I setup the following circuit: When I measure the voltage between GND and INPUT of the LM7805CV I have a voltage of 7.9V (around 8V as per power supply). But when I measure the output it is only 1.4V ...
sesc360's user avatar
  • 297
1 vote
1 answer
1k views

Voltage regulator replacement

I have a gadget (a Sonar) that stopped working (doesn’t respond to power on, power led does not turn on) and opening it to look for the typical signs of failure I see an L7818 voltage regulator in TO-...
Anders Forsgren's user avatar
4 votes
3 answers
18k views

Connecting Voltage Regulators 7812 in Parallel for High Current [duplicate]

Could I use two L7812 voltage regulator ICs in parallel to get 12 volt and more current that with just one?
payton_2624784's user avatar
-1 votes
2 answers
724 views

LM338T Output to 5V issue with LM1085-IT 3.3V

I am using 12V , 2A DC power supply as an input to LM338T and LM1085-IT 3.3 , for 5V and 3.3V output respectively. The issue i am facing here is when these both voltage regulators are connected in ...
KarmaCoding's user avatar
5 votes
4 answers
4k views

Does the output bypass capacitor of an LM7805 double as a decoupling capacitor?

I'm using a 5v linear regulator (specifically an LM7805) that outputs directly to an ATMEGA328P. According to the LM7805 datasheet (page 23) input and output bypass capacitors should be used, as seen ...
Gabe S.'s user avatar
  • 303
5 votes
2 answers
13k views

LM7812 and decoupling capacitor value

LM7812 voltage regulator is recommended to be used with decoupling capacitors at its input and output as in the below diagram: And here is the part from the manufacturer Fairchild(see recommended C1 ...
floppy380's user avatar
  • 1,885
0 votes
2 answers
277 views

Crude LM7809 9V NiMH charger

I want to charge my 9V NiMH cell with a LM7809. The problem is that I want to limit the current output to 20mA or 30mA. How can I limit the current output from that voltage regulator with simple ...
Kokachi's user avatar
  • 690
0 votes
2 answers
2k views

LM78xx Reverse Polarity and Reverse Bias

I'm building a circuit that will use a LM7805 and LM7812 to produce 5VDC and 12VDC respectively, with the input power being ~16VDC from an external wall wart. I already fried one of each regulator ...
RobotAndy's user avatar
  • 245
6 votes
1 answer
1k views

What does the CT suffix stand for in voltage regulator?

Given a regulator such as the LM7812, what does the CT suffix stand for in a voltage regulator in Fairchild LM7812CT)? I've googled and went through the related datasheets, but could not find the ...
Pedro Lopes's user avatar
2 votes
5 answers
248 views

Do 74HCxx chips require a linear voltage generator?

Recently I've read a book that says it's absolutely necessary to use a linear voltage regulator like LM7805 in circuits that use any of 74HCxx chips (CMOS logical gates). I thought that this advice is ...
Aleksander Alekseev's user avatar
1 vote
2 answers
2k views

LM7805CV output voltage drop to 2.5v after connecting load

I've made a simple linear power supply for micro-controller with a transformer and LM7805CV as seen in the picture. LM7805CV input voltage is 35V and output without load is 5V but after connecting a ...
sDev's user avatar
  • 55
2 votes
2 answers
1k views

Jumper out an LM7805

I have a 5V hobby circuit that will be externally powered from a wall wart, with way less than 1 amp. For full flexibility, I'm thinking of using a simple LM7805 regulator - but that has a 7V minimum. ...
John Burger's user avatar
  • 1,493
-1 votes
2 answers
317 views

buck converter and regulator

First: I want to use DC DC Stop Down Buck Converter, im using this one: - https://www.aliexpress.com/item/10pcs-24V-12V-to-5V-3-3V-3V-DC-DC-1A-Step-Down-Converter-Voltage-Regulator/32671102728.html ...
bosko's user avatar
  • 1
1 vote
3 answers
4k 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 ...
Misal313's user avatar
2 votes
6 answers
2k views

Running Regulator Under Voltage

Is there any disadvantage to running a Linear Regulator under the minimum voltage stated in the datasheet? For instance, In the datasheet of the LM7812C2T, it says the minimuim voltage in order to to ...
GumboMcGee's user avatar
0 votes
2 answers
273 views

Decoding power supply regulation (42V from 5V)

I am referring below schematic where 42V is generated from LM78L05 regulator IC. But I am not able to get how LM78L05 can generate 42V? Which concept is used to get such high voltage from 5V regulator ...
Electroholic's user avatar
0 votes
2 answers
164 views

Solar cells with 5v regulator: would it supply more current than available?

I recently bought online three solar panels rated 6v x 500 mA for some circuits I had in mind. What I got instead were 12v cells, and I am certain they are rated 250mA, since the seller had those too. ...
Giordano Bruno's user avatar
0 votes
1 answer
400 views

AC supply to digital output

I need to sample 8 power switches connected to 230 Volt supply. I want to record the status of these switch every 10 seconds and send to cloud for which I am using arduino with ethernet shield. For ...
user1789034's user avatar
-1 votes
2 answers
338 views

xV input from a wall wart to +9v, -9v, +9v output

I am trying to modify a circuit Circuit schematic that requires three 9v batteries. Two to supply +9v/-9v for an lm358N opamp, the other +9v is to drive a DMM display. I have dozens of wall warts of ...
GregMa's user avatar
  • 111
4 votes
4 answers
2k views

Switch Mode Alternative to LM7805/LM7905

I am attempting to design a dual rail power supply PCB for a university project. There are a number of restrictions - namely that it maintains > 80% efficiency regardless of the current draw. I was ...
JosephGarrone's user avatar
1 vote
0 answers
43 views

Question regarding the LM7810 voltage regulator [duplicate]

Is there a simple way I can hook up this regulator to reduce the maximum output current from the 1A rating down to a 500mA maximum output without affecting the 10vdc output?
user80773's user avatar
8 votes
3 answers
8k views

Making LM78xx fail safe against short, open, reverese bias, flyback, etc

I want to use LM78xx for various applications. What I am concerned about is its failure modes. 1. Failure to Short Not shorting Vcc to ground!! I mean shorting V_input to V_output. Assume that you ...
arudino.tyro's user avatar
10 votes
3 answers
11k views

How to select proper capacitors and capacitance for LM78xx voltage regulators?

I want to use LM78xx voltage regulators for various projects. I want to know in general, how should I choose a correct value for input and output capacitors of LM78xx family when I want to change DC ...
arudino.tyro's user avatar