# Questions tagged [lm78xx]

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

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### 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!
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### the 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. ...
137 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 ...
781 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 ...
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### 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 ...
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### 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: ...
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### 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 ...
813 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 ...
168 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 ...
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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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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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....
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### 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 ...
186 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?
440 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 ...
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1 vote
714 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-...
14k 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?
583 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 ...
3k 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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
1k 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 ...
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### 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. ...
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### 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 vote
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 ...
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### 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 ...
206 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 ...
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### 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. ...
352 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 ...
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### 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 ...
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### 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 ...
1 vote
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### 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?
7k 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 ...
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### 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 ...
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### 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 ...
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### 78L05 questions [duplicate]

What are the capacitors on the input and output of a 78L05 for? I saw a lot of different schematics with a lot of different input and output capacitor values. So now I am really confused, and I'm ...
2k views

### 48V DC Power Supply Using LM7812 in Series

I want to create a 600W 48 VDC power supply with input taken from the line (220VAC) and so far the steps that I've had in my mind are: Stepping-down the voltage to 15V using transformer with 3A ...
2k views

### 7809 Linear Voltage Regulator Outputs in Series

I'm building a linear power supply that converts 120VAC mains voltage into multiple 9VDC, isolated outputs. I'm using this transformer that has the proper primary winding and 8 secondaries that I'll ...
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### Can a 5V regulator connect directly to a voltage divider to obtain a 2V output?

In my circuit, a lm78l05 is used to provide +5V voltage to other parts. And now I need another +2V source to shift my input signal from +-2V to 0~4V as the ADC ad7682 limits the input signal range ...
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### Can I obtain a new voltage source from outputs of two cascaded linear voltage regulators in practice?

I have a device which works with 7V. I have a 7812 and 7805 already running in the circuit. Can I use the outputs of this voltage regulators to feed the 7V device? I know this is possible in theory. ...
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