Questions tagged [lm78xx]

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

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245 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 ...
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1answer
882 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....
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86 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 ...
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1answer
62 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?
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233 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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1answer
205 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-...
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3answers
6k 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?
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2answers
324 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 ...
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4answers
2k 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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2answers
5k 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 ...
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2answers
184 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 ...
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2answers
605 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 ...
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1answer
427 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 ...
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5answers
183 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 ...
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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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2answers
957 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. ...
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2answers
261 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 ...
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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 ...
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6answers
767 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 ...
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2answers
132 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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2answers
95 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. ...
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1answer
313 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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2answers
252 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 ...
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4answers
1k 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 ...
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0answers
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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?
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3answers
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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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3answers
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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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3answers
1k 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 ...
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3answers
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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 ...
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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 ...
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2answers
1k 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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4answers
365 views

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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3answers
870 views

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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3answers
675 views

Is a full-wave rectifier really required with a 7810 regulator?

I'm possessed of a 12-0-12 500mA transformer. To supply a stable 10V, I seek to connect a bridge rectifier, roughly filtered with a 1000uF/50V electrolytic capacitor and a 7810. Is a bridge, or ...