Questions tagged [lm78xx]
LM78xx are a popular series of linear voltage regulators. To name a few 7805, 7809, 7810
56
questions
0
votes
4
answers
118
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 ...
1
vote
1
answer
110
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 ...
- 13
3
votes
1
answer
92
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 ...
- 33
0
votes
0
answers
39
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 ...
- 33
0
votes
2
answers
241
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 ...
- 15
0
votes
2
answers
134
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.
...
- 103
1
vote
2
answers
364
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 ...
- 239
0
votes
2
answers
107
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 ...
- 239
0
votes
4
answers
171
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 ...
- 105
-3
votes
3
answers
410
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!
- 27
0
votes
3
answers
1k
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.
...
- 198
0
votes
2
answers
250
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 ...
- 136
3
votes
3
answers
1k
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 ...
- 323
0
votes
0
answers
78
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
...
3
votes
2
answers
556
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:
...
- 31
3
votes
1
answer
351
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 ...
0
votes
2
answers
1k
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 ...
0
votes
1
answer
256
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 ...
- 863
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 ...
- 481
1
vote
4
answers
181
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 ...
- 199
0
votes
1
answer
167
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 ...
- 113
0
votes
3
answers
1k
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 ...
- 602
3
votes
1
answer
7k
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 ...
- 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....
- 91
0
votes
1
answer
106
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 ...
-3
votes
1
answer
232
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?
- 1
3
votes
1
answer
520
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 ...
- 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-...
- 113
4
votes
3
answers
17k
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?
-1
votes
2
answers
660
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 ...
- 11
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 ...
- 303
5
votes
2
answers
12k
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 ...
- 1,725
0
votes
2
answers
262
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 ...
- 668
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 ...
- 245
5
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 ...
- 153
2
votes
5
answers
235
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 ...
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 ...
- 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. ...
- 1,493
-1
votes
2
answers
313
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
...
- 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 ...
- 35
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 ...
- 21
0
votes
2
answers
245
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 ...
- 729
0
votes
2
answers
161
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.
...
0
votes
1
answer
378
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 ...
-1
votes
2
answers
331
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 ...
- 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 ...
- 165
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?
- 11
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 ...
- 694
10
votes
3
answers
10k
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 ...
- 694
0
votes
3
answers
2k
views
LM7915 delivering more than -15v
I'm trying to build a regulated power adapter using LM7915.
Before everything, I built on a protoboard the schema included on the datasheet (from ST). But, instead -15v, the output is -19v...
I'm ...
- 175