[Regulated Dual Supply ] Easyeda 7805 7905 Pin error?

  Xons, 2 weeks ago

https://easyeda.com/Xons/New_Project-888e4e096f92411e906b0e7d6ff54279

7805- pin 1-in gnd-2 out-3

Is this a mistake?
Is the circuit correct?
i have in AC 15V out AC 5V

Thanks for any assistance

Comments

alexbbuy

It is indeed a mistake. Both the 7805 and 7905 have GND on the middle pin.
See this: https://electronicsforu.com/wp-contents/uploads/2016/10/Lm7805-pinout-diagram-300x238.png

andyfierman

We will check the pinouts but before you go any further with this project you need to think very carefully about your design.

It does not work and will destroy almost all the components on the PCB as soon as you switch it on!

To understand why let's look at what happens on a negative half cycle of the AC input.

If you apply a negative voltage to the 7805 input and a positive voltage to the 7809 input then you will destroy the electrolytic caps on the input side and the diodes you have across the regulators and from their outputs to ground will be forward biased and so will sort out the AC input voltage and will therefore burn out.

If the diodes blow open circuit then the regulators and the electrolytic caps across the outputs will also then be reverse biased and so will blow.

Xons

enter link description here

What should I do?

Is that okay?

andyfierman

You need to add a diode in series with the input to each side.

Even with these diodes, depending on the input voltage and frequency the performance of your circuit may not be what you expect due to the turn on and turn off behaviour of these regulators.

You could try simulating the circuit using the 7805EE and 7905EE models.

For more see:

https://easyeda.com/andyfierman/Welcome_to_EasyEDA-31e1288f882e49e582699b8eb7fe9b1f

Xons

I don't understand this

Circuit: gooduntitled

Doing analysis at TEMP = 27.000000 and TNOM = 27.000000

Note: Starting dynamic gmin stepping
Note: One successful gmin step
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Note: One successful gmin step
Note: One successful gmin step
Warning: Dynamic gmin stepping failed
Note: Starting source stepping
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Note: One successful source step
Warning: source stepping failed

Transient solution failed -

Last Node Voltages

Node Last Voltage Previous Iter


volprobe3 4.70804 4.70803
volprobe4 -4.69015 -4.69016
volprobe2 -2.34163 -2.34519 *
volprobe1 2.35241 2.3524
v1#branch -1.225e-08 -1.225e-08

doAnalyses: Too many iterations without convergence

tran simulation(s) aborted
Error(parse.c--checkvalid): volprobe1: no such vector.
ngspice-26 done

LISA_DALTON

I am NOT trying to be mean, just realistic.

In all honesty, there is NOTHING right with this circuit!
You need to either have someone who understands electronics, build what it is you need,
or go to school and spend 2 years getting a degree. Then take a look at this, and feel silly.
Don't ask the folks here to correct you, as they don't have the time to do all the work for you.

If you saw a car sitting on it's brake rotors, wheels and tires tied to the roof, and the engine chained to a
trailer hitch laying on the road, and the owner asked you, "What's wrong with this"?
Would you start trying to explain how a car worked? Or just tell him to have it taken to a mechanic?
Well that's what I see, when I looked at your circuit.

Thanks for the laugh though, I pinned the schematic up over my monitor.
And stay away from wall 120 volts. : )
Good luck in school.
-Lisa

LISA_DALTON

@alexbbuy
It doesn't matter, there is no ground connection on the input or output plug anyway.
This is a very short term smoke generator.

Xons

enter image description here

Should this be a normal 5V output
error?

andyfierman

@Xons,

The circuit you are tinkering with is not going to "work", (however you define "working" in this context).

Stop wasting your time on it and think carefully about what exactly it is that you are trying to do.

Write yourself a design requirement discussion that answers questions like these:

What is the exact purpose of your circuit?

What does the source supply come from?

What load does it have to drive?

How much load current?

What frequency is the AC supply?

What waveform is the input supply?

What waveform do you require at the output?

What short circuit protection do you want on the output?

What over overvoltage protection do you want on the output?

Read the wiki page for the 78xx regulator.

Find and read the datasheets and applications notes for the 78xx and 79xx family regulators from TI, OnSemi and ST.

andyfierman

@Xons, @Alexbbuy,

The pinouts shown on the EasyEDA schematic symbols for the LM78xx and L78xx family devices and on the LM79xx and L79xx family devices are correct.

The LM78xx type family of regulators have a pinout as shown in Figure 2 of:

http://www.st.com/resource/en/datasheet/l78.pdf

enter image description here

and the front sheet of:

https://www.fairchildsemi.com/datasheets/LM/LM7805.pdf

enter image description here

The LM79xx type family of regulators have a pinout as shown in Figure 2 of:

http://www.st.com/resource/en/datasheet/l79.pdf

enter image description here

and the front sheet of:

http://www.onsemi.com/pub/Collateral/LM7918-D.pdf

enter image description here

  • Please check manufacturers' datasheet information carefully before querying pinout and package information.

Thanks.

andyfierman

@alexbbuy,

Please see the above.

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