Power supply problems - l7805 on breadboard

[harvin dhillon]

how to put l7805 on breadboard

Ok I have a 240V to 6V AC transformer. It has a maximum current output of 1.2A.

I connected it to a diode rectifier and it produces 6.45V DC. When I connect this to my micro controller circuit, the micro controller doesnt initialize and my circuit doesnt work.

Then I checked and saw that the voltage was around 4.41V at the micro controller VDD.

The LCD connected to the micro controller doesnt show anything just half of the first row black boxes.

Any ideas on why?

This is my microcontroller circuit if it helps...

**broken link removed**
Basically I control an AC heater load via a optocoupler. Rather than powering the microcontroller circuity with Batteries I want to use the same plug point as the heater through a transformer of course...

 

[wp100]

how to connect 5.1 zener to 7805 regulator output

Hi,

Taking what you have said literally then I cannot see your circuit working.

The micro chips need a regulated 5v DC to work.

If you have just used a transformer, a diode or diode block and fed that voltage to the +5vdc line of the chips then its possible everything has blown.

To check if anything does still work then use 4.5v of battery power and measure the current which should be under 20ma dc

The black boxes on the lcd are a good sign, it means it is functioning to some degree, just not getting anything from the micro.

Out of interest whos project /software code is it ?


There are a couple of other errors on your circuit but nothing that would blow it up.

 

[harvin dhillon]

Re: Transformers

Hi,

Taking what you have said literally then I cannot see your circuit working.

The micro chips need a regulated 5v DC to work.

If you have just used a transformer, a diode or diode block and fed that voltage to the +5vdc line of the chips then its possible everything has blown.

To check if anything does still work then use 4.5v of battery power and measure the current which should be under 20ma dc

The black boxes on the lcd are a good sign, it means it is functioning to some degree, just not getting anything from the micro.

Out of interest whos project /software code is it ?

Hi mate,

The circuit still works actually. It is my project for my degree in Uni but I am having some problems. It is a weird problem. One of many.

I actually have a 9V DC adaptor (Measured at 13V DC with multimeter) plugged in a 7805 voltage regulator. But the output voltage is never regulated 5V... I cant figure out why, it always comes out as 8V. Currently I just placed a small 33Ohm resistor before the input of the voltage regulator to drop the voltage. Only then the output is 4.8V.

This shouldnt be the way however. Shouldnt the voltage regulator output 5V?

Currently I just have the circuit on a breadboard as I dont want to solder everything until I solve this problem. Could it be that the breadboard is shorting something? I am not sure how as everything is working as it should

I thought it could be the DC adaptor hence why I tried the transformer and the question above

What other errors are you mentioning there mate?

Thanks for the reply

 

[GSM Man]

Transformers

Why don't you post a schematic of your power supply - obviously you have something connected incorrectly.

 

[harvin dhillon]

Re: Transformers

Why don't you post a schematic of your power supply - obviously you have something connected incorrectly.

Nothing really in the power supply. I just connected according to the schematic in the 7805 data sheet. I tried it with and without the caps. Just the same...

 

[wp100]

Re: Transformers

hi,

As GSM Man said you must have something seriously wrong somewhere.

Your high meter reading at 13v are probably ' no load' readings.

To check the regulator is working put a small led via a 220ohm resistor across the +5v regulator output , then measure the voltage across the regulators output and 0v

If its not very close to +5v then the regulator circuit or your meter are faulty and need sorting out - no way will the pic behave if the psu is up the creek.

If the software is yours, then the best way is to test it out with just the pic and lcd then add on the other stuff one at a time, the triac / mains at the very end.

On your circuit diagram, the switches will never work, the Pull down resistors should be 1K - if you use them in pull up then 10K is better.

Have not checked, but the led connections on the opto coupler may be the wrong way round - worth you checking

 

[harvin dhillon]

Transformers

Now that I have seen the diagram, the push buttons are drawn incorrectly lol. They are working fine. I push them and the PIC responds to them correctly. I changed them to 1.2K and the problem is still there. I tested the circuit with two 7805 ICs so that shouldnt be the problem.

Could it be some short circuit on the breadboard?

Oh yeah and the code is mine. I wrote it in MikroBasic. I think is more of a hardware problem than software though... Am I right?

 

[wp100]

Re: Transformers

Hi,

Its a bit difficult to tell whats wrong if what you tell us is not right ..

If in doubt , always go back a few steps - why not just use the pic and a led to do a simple flasher - then at least you know the pics ok.

 

[betwixt]

Re: Transformers

I agree with the other posts, something is seriously wrong with your 7805 regulator and you absolutely must use a regulated supply.

Never, never, never use 780x or 790x regulators without at least a capacitor across the input to ground and it must be close to the regulator. These devices contain high gain error amplifiers and will go unstable unless the input is closely decoupled. Your strange 8V may be the result of instability. I have seen these things dump an amp of current at 1.5MHz when used without an input capacitor so they can be quite potent sources of nasty signals. If instability was the problem, you could well see 8V on a a normal test meter, only an oscilloscope would show the real output.

You *might* get away with a 5.1V Zener diode as a shunt regulator instead of the 7805 but you would have to ensure you used a suitable series resistor with value that could still let it regulate when the extra current of the opto-isolator was drawn.

Brian.

 

[harvin dhillon]

Re: Transformers

Well it is really weird. I got three of these L7805CV regulartors and they all arent giving me 5V output. I tested all three with a resistor and LED and measured the voltages and they all are giving me an 11V output?

However when I use a 12V regulator CUE7812C with the same setup as above, then the output is 12 as it should. When I use this on my circuit, I get a 4.57V output. Weird.... I thought it could be my adapter so I switched it with 12V batteries as similar outcomes.

Have i gotten the wrong type of 5V regulators?

Cause I checked my circuit and there arent any wrong connections that I know off or shorts.

Any more ideas mates?

 

[pranam77]

Power Supply Problems...

There is nothing like wrong type of 5volt regulators. If you are using LM7805 (TO220 package) and wired the left pin to input, Centre to ground, and Right pin as out put, You should get 5 volts. May be there are chances you get 5.01 or 5.015 on the multimeter. 78L05 which comes in T092 package will have the reverse pins for input and output. The centre pin will be ground. Good luck

 

[wp100]

Re: Power Supply Problems...

Hi,

If you run a 12v regulator from a 12v battery you would probably not get 12v output because the regulator needs at least 14-15v input to provide the regulated 12v output.

This data sheet shows the correct pinout and simple circuit - virtually any similar capactitors .01 to 100uf on the input and output will work for the sake of testing.
http://www.datasheetcatalog.org/datasheet/stmicroelectronics/2143.pdf

With a 12v battery on the input and a led/resistor across the output you should get a good +5v on the output.

To confirm the T0220 regulators pin out , with the part in front of you, with the lettering facing you, the metal tab at the top and the pins at the bottom -
the left pin is Input, center 0v, right pin +5v out.

If you not getting +5v give or take 0.1v, then something is still wrong - all 3 regulators could be connected wrong, be faulty or your meter is faulty.

Possibly a more simple answer might be that you have your meter set incorrectly such as on AC volts intsead of DC volts ?

 

[harvin dhillon]

Power Supply Problems...

Aye ok it was my stupidity, seems I got the inputs wrong

Working fine now . Thanks guys...

Still though with the transformer. It is giving me 4.4V after regulation. Should be enough to turn on the circuit but all it does is shows the bars on LCD screen and seems to be a slight flicker. I got the correct caps on the regulator and the rectifier is a full wave rectifier. Any other possible problems?

 

[wp100]

Re: Power Supply Problems...

Hi,

Well glad you spotted that mistake - we all make them.

As to your 4.4v there is 2 possibilities.

Either your power pack cannot deliver enough power to drive your circuit - which would be surprising, because your circuit should only take about 20 -30 ma.

Does the heatsink tab of the 5v regulator get too hot to hold between your fingers - carefull !

The other thing is that something on the circuit is shorting and pulling the voltage down - to check this you need to measure the DC ma current to the circuit at the point between the regulator output and the circuit positive input.
If its a lot more than above, then disconnect each item in turn to locate the short.

One other thing about you circuit diagram - you show pin 15 / 16 connected to +5v and 0v.
Thats wrong in that those connections are for the lcds backlight leds and typically run at 4.2v max - so it you have them connected to +5 they will be very bright and will soon burn out - as well as taking a lot of current.

 

[harvin dhillon]

Re: Power Supply Problems...

Aye thanks again. The voltage regulator was very hot but now that I placed a 33Ω resistor at the positive terminal of the backlight the regulator has cooled down considerably

I still cant get the transformer to power up the circuit though. I'll get hold of a 12VAC transformer tomorrow and see if that works

Thanks again.

 

[wp100]

Re: Power Supply Problems...

Hi,

Most standard lcds don't actually need the backlight to work, so you can probably leave pins 15 /16 disconnected.

You really do need to measure the ma current on the output from the regulator, this will tell you if you still have a short or some sort - using more that 20 -25ma would indicate a fault.
Just google if you are not sure how to measure dc current - plenty of tutorials there.
When your current is nearer 20ma the voltage should similarly be stable at 5v.

Untill your circuit and voltage is good there is little chance of the program running in the Pic chip.

An important point when using a crystal is how you are using it - are you on a soldered board or breadboard ? - the connectors between the pic, crystal and its caps need to be really good with very short wires - otherwise all sorts of trouble can be expected - not running being the main one.

The led connections to the opto coupler look wrong to me - try disconnecting it while doing these tests.

 

[harvin dhillon]

Re: Power Supply Problems...

Thanks mate. You guys been really helpful.

Actually the problem was noise from the DC Output of the transformer. I was only using 1uF and 10uF caps in parallel. I changed them to 10uF and 100uF and it now works as it should

 

[wp100]

Re: Power Supply Problems...

Hi,

Thats good to know its working ..

 

[JoKKeR]

Re: Transformers

Hi,

Taking what you have said literally then I cannot see your circuit working.

The micro chips need a regulated 5v DC to work.

If you have just used a transformer, a diode or diode block and fed that voltage to the +5vdc line of the chips then its possible everything has blown.

To check if anything does still work then use 4.5v of battery power and measure the current which should be under 20ma dc

The black boxes on the lcd are a good sign, it means it is functioning to some degree, just not getting anything from the micro.

Out of interest whos project /software code is it ?


There are a couple of other errors on your circuit but nothing that would blow it up.

Btw. 4.5V i not enough, because 20 Mhz oscillator is in use.