78XX voltage regulator problem

[christos]

why does every time i use a 7808 voltage regulator always burns????first time i used 15v input=dead
second time i used 12v=dead  third time 10volts=dead...NO shortcircuit ..1 pin is input,2 pin is ground and 3 pin is output for the 7808 and for thr 7908 is 1pin for ground,2 pin for input and 3 pin for output
i got 100% dc voltage input
i use this one  l7808cv 
i bought 5 more from a difrend store
can someone tell me the max input

[tszaboo]

It is not about the input voltage, it is probably about the dissipation. If you dont use a heatsink, you can only dissipate about 2 watt. That is about 250mA for 12V. Use a heatsink? How much current are you pulling?

[Rudane]

Are you using a heatsink?

[Monkeh]

why does every time i use a 7808 voltage regulator always burns????first time i used 15v input=dead
second time i used 12v=dead  third time 10volts=dead...NO shortcircuit ..1 pin is input,2 pin is ground and 3 pin is output for the 7808 and for thr 7908 is 1pin for ground,2 pin for input and 3 pin for output
i got 100% dc voltage input
i use this one  l7808cv 
i bought 5 more from a difrend store
can someone tell me the max input

Sorry, but you're going to have to go read and understand the datasheet. Just like the manual for that Keithley. Reading is not optional.

[christos]

It is not about the input voltage, it is probably about the dissipation. If you dont use a heatsink, you can only dissipate about 2 watt. That is about 250mA for 12V. Use a heatsink? How much current are you pulling?

i use heatsink..5x5  and 1amp fuse..but the regulator always gets burnd..how much input should i use max-min

[christos]

why does every time i use a 7808 voltage regulator always burns????first time i used 15v input=dead
second time i used 12v=dead  third time 10volts=dead...NO shortcircuit ..1 pin is input,2 pin is ground and 3 pin is output for the 7808 and for thr 7908 is 1pin for ground,2 pin for input and 3 pin for output
i got 100% dc voltage input
i use this one  l7808cv 
i bought 5 more from a difrend store
can someone tell me the max input

Sorry, but you're going to have to go read and understand the datasheet. Just like the manual for that Keithley. Reading is not optional.

i did read the datasheet ..i had some 7805 and replaced the 08 with the 05 and it worked fine..5.1 volts output..put back the 08 and burnd the 4th today ..i did this before 10mins..its the regulator..something is wrong with that..

[christos]

anyway..i ordered some more 7808..hope they dont get burnd

[sync]

i did read the datasheet ..i had some 7805 and replaced the 08 with the 05 and it worked fine..5.1 volts output..put back the 08 and burnd the 4th today ..i did this before 10mins..its the regulator..something is wrong with that..

What capacitors do you use?
And how near they are connected to the 7808?

[christos]

i did read the datasheet ..i had some 7805 and replaced the 08 with the 05 and it worked fine..5.1 volts output..put back the 08 and burnd the 4th today ..i did this before 10mins..its the regulator..something is wrong with that..

What capacitors do you used?
And how near they are connected to the 7808?

2x2200 uF and like 2cm away from the last cap

[sync]

Maybe it oscillates (to death). Add one 0.1uF ceramic cap at the input and one at the output of the 78xx. As near as possible. 2cm is too long. And don't use big caps at the output.

[christos]

Maybe it oscillates (to death). Add one 0.1uF ceramic cap at the input and one at the output of the 78xx. As near as possible. 2cm is too long. And don't use big caps at the output.

why near? at the output i use 10 uf

[arcom]

Could also be fake ICs especially if the 7805 works and 7808 blows up. I always found the 78XX regulators very difficult to kill since they are pretty well protected. Their only weakness is when the output voltage is higher than the input voltage in which case a diode from output to input fixes the problem.

[christos]

Could also be fake ICs especially if the 7805 works and 7808 blows up. I always found the 78XX regulators very difficult to kill since they are pretty well protected. Their only weakness is when the output voltage is higher than the input voltage in which case a diode from output to input fixes the problem.

Fake??i blow up 4 of them today and the 7805 works fine with 10 volts input....ill wait for hte next order to see if they will work fine..

[Lurch]

i blow up 4 of them today

I think you need to review your test procedures.

[christos]

i blow up 4 of them today

I think you need to review your test procedures.

ill try first with the new ones that i ordered and if i blow them too ill review it

[henson]

Maybe you should post a picture of your set up. Something doesn't seem right. You should have plenty of capacitance to avoid oscillation and you really aren't dropping the voltage to much to kill them by heat. Very suspicious.

[kripton2035]

what power do you dissipate in the regulator ?
what is the voltage input, the output should be 8v and what is the current throught it ?

[christos]

what power do you dissipate in the regulator ?
what is the voltage input, the output should be 8v and what is the current throught it ?

i use a transformer 10 v and 2 amps output

[christos]

Maybe you should post a picture of your set up. Something doesn't seem right. You should have plenty of capacitance to avoid oscillation and you really aren't dropping the voltage to much to kill them by heat. Very suspicious.

if the same thing happens with the new ones i ordered..ill make a vid how the 08 regulator burns and with the same pcb but with the 05 regulator at 10 volts 2 amp input.. may all four of the 08 regulators was bad..

[Lurch]

what power do you dissipate in the regulator ?
what is the voltage input, the output should be 8v and what is the current throught it ?

i use a transformer 10 v and 2 amps output

You may want to read the datasheet, as already mentioned.

[tasos987]

I'm sorry to say that YOU HAVE TO read the datasheet

[christos]

I'm sorry to say that YOU HAVE TO read the datasheet

yea i DID IT 5 TIMES..if you live in greece then you know poso lamogia einai oli tous and sorry about not writing in english..many people in greece are like thiefs...they sell many times items that are dead or the buy things that have some kind of malfunction and sell them to us

[christos]

I'm sorry to say that YOU HAVE TO read the datasheet

yea i DID IT 5 TIMES..if you live in greece then you know poso lamogia einai oli tous and sorry about not writing in english..many people in greece are like thiefs...they sell many times items that are dead or the buy things that have some kind of malfunction and sell them to us

for example ,when i bought a soldering station the ct -936..i got it with the knob broken ..

[Lurch]

OK, well this seems to be going nowhere.

[tasos987]

OK, well this seems to be going nowhere.

Obviously....
+1

[christos]

so it ends here..ill post on this one if the new l7808 works

[Monkeh]

I'm sorry to say that YOU HAVE TO read the datasheet

yea i DID IT 5 TIMES..if you live in greece then you know poso lamogia einai oli tous and sorry about not writing in english..many people in greece are like thiefs...they sell many times items that are dead or the buy things that have some kind of malfunction and sell them to us

Okay then, what's the maximum input voltage? What does it say about input and output capacitance?

[mariush]

Do you convert the voltage from the transformer to DC before it gets to the 7808 ?

Transformer output is AC, regulators work with DC voltage. You have to use a bridge rectifier or at least one diode and then some capacitors to get DC voltage from the transformer.
Is the output of the transformer 10 volts DC AFTER rectification and after using a capacitor, or  it says 10 volts on the transformer label?

Regulators in the 7800 family need 2 volts ABOVE the output voltage to work. A 7808 will need AT LEAST 10v to output a stable 8v. This is mentioned IN THE DATASHEET.

for example ,when i bought a soldering station the ct -936..i got it with the knob broken ..

A knob can be broken during shipping, you can return a broken product and ask for another one or your money back.  You're in European Union, so you order something and have it shipped to you, you have the right by law to return anything for your money back, no questions asked, within 10 working days of your purchase.  if the seller doesn't agree to send you another knob or change your product, ask for money back within the 10 days allowed by law.

[Kappes Buur]

Maybe you should post a picture of your set up. Something doesn't seem right. You should have plenty of capacitance to avoid oscillation and you really aren't dropping the voltage to much to kill them by heat. Very suspicious.

if the same thing happens with the new ones i ordered..ill make a vid how the 08 regulator burns and with the same pcb but with the 05 regulator at 10 volts 2 amp input.. may all four of the 08 regulators was bad..

Do you have a circuit something like this



C1 and C2 should be as close as possible to the regulator.

[edit]
I just noticed, C1 should have said 0.33uF.

[Monkeh]

I just noticed, C1 should have said 0.33uF.

And this, kids, is why we say 0u33 or 330n.

[christos]

Do you convert the voltage from the transformer to DC before it gets to the 7808 ?

Transformer output is AC, regulators work with DC voltage. You have to use a bridge rectifier or at least one diode and then some capacitors to get DC voltage from the transformer.
Is the output of the transformer 10 volts DC AFTER rectification and after using a capacitor, or  it says 10 volts on the transformer label?

Regulators in the 7800 family need 2 volts ABOVE the output voltage to work. A 7808 will need AT LEAST 10v to output a stable 8v. This is mentioned IN THE DATASHEET.

for example ,when i bought a soldering station the ct -936..i got it with the knob broken ..

A knob can be broken during shipping, you can return a broken product and ask for another one or your money back.  You're in European Union, so you order something and have it shipped to you, you have the right by law to return anything for your money back, no questions asked, within 10 working days of your purchase.  if the seller doesn't agree to send you another knob or change your product, ask for money back within the 10 days allowed by law.

9.8 volts dc 100%(got osciliscope) before the regulator

[christos]

Maybe you should post a picture of your set up. Something doesn't seem right. You should have plenty of capacitance to avoid oscillation and you really aren't dropping the voltage to much to kill them by heat. Very suspicious.

if the same thing happens with the new ones i ordered..ill make a vid how the 08 regulator burns and with the same pcb but with the 05 regulator at 10 volts 2 amp input.. may all four of the 08 regulators was bad..

Do you have a circuit something like this



C1 and C2 should be as close as possible to the regulator.

[edit]
I just noticed, C1 should have said 0.33uF.

yes but without the D2..why does the cap need to be close to the regulator??

[underwurlde]

^ Inductance old boy.

What is it powering? How much capacitance connected to output?

Too much capacitance on output = large in-rush current upon powering up = not great.

A

[Kappes Buur]

yes but without the D2..

With 78xx regulators you should always include D2. This will protect the regulator if the input voltage suddenly collapses and the output voltage is trying to feed back into the regulator.

[edit]
I see arcom also mentioned this on page 1

why does the cap need to be close to the regulator??

For stability reasons. Well, this is not a hard and fast rule but it is common sense.
It just won't do to have the regulator on one end of a pcb and those capacitors on the far end. Thusly, as close as possible.

[sleemanj]

Replace the load with resistors to get you about 100mA, see if it works, increase to 150, 200, 250.... until it craps out.


Probably "chinese domestic market" parts which don't meet the specs of "the real deal", or simply outright fake.

[christos]

as you said..chinese all four of them .anyway..im out of 7808..waiting for the new order

[arcom]

You know you can use 7805 to get 8V?
Just put a voltage divider at the output and connect the GND terminal to the divider, just like an LM317.

You have a table here with suggested resistor values: http://www.rason.org/Projects/regulator/regulator.htm

Unless you absolutely need an LM7808, in which case please ignore my post

[christos]

You know you can use 7805 to get 8V?
Just put a voltage divider at the output and connect the GND terminal to the divider, just like an LM317.

You have a table here with suggested resistor values: http://www.rason.org/Projects/regulator/regulator.htm

Unless you absolutely need an LM7808, in which case please ignore my post

why ignore it..i didnt know that   well..i bought today a 7808 and it works fine..thx for the help

[lapm]

After quick read im thinking you are drawing too much current throw the regulator, leading to massive power transformed to head and your regulator deep frying itself in result.

Douple, triple check the pinout. Read datasheet. Anything about maximum limits...

Some regulators metal tab is connected to one of the terminals internally. Very easy to miss and cause short that takes out component. Yes even i have been bited by this.

Also consider bossibility that if everything else fails, you might have fake component. Im lucky and havent run into one of those yet, but one of these days. One of these days i will.

[deth502]

guys, my 1A v-reg is blowing up when i try to run 2A through it?

boy, that one is a mystery.

i believe i have seen at least 5 posts here recommending to read the data sheet.

78xx series datasheet:

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

[hobbes]

guys, my 1A v-reg is blowing up when i try to run 2A through it?

boy, that one is a mystery.

i believe i have seen at least 5 posts here recommending to read the data sheet.

One might wonder what those "SOA protection" and "Thermal protection" in the said data sheet are there for?

[lapm]

guys, my 1A v-reg is blowing up when i try to run 2A through it?

boy, that one is a mystery.

i believe i have seen at least 5 posts here recommending to read the data sheet.

One might wonder what those "SOA protection" and "Thermal protection" in the said data sheet are there for?

Well protection seems to be working. It disables system to stop overload occurring again..

[sleemanj]

One might wonder what those "SOA protection" and "Thermal protection" in the said data sheet are there for?

The presence of such in 78xx  from China is not assured.   Neither is current capacity, or power dissipation.

[christos]

After quick read im thinking you are drawing too much current throw the regulator, leading to massive power transformed to head and your regulator deep frying itself in result.

Douple, triple check the pinout. Read datasheet. Anything about maximum limits...

Some regulators metal tab is connected to one of the terminals internally. Very easy to miss and cause short that takes out component. Yes even i have been bited by this.

Also consider bossibility that if everything else fails, you might have fake component. Im lucky and havent run into one of those yet, but one of these days. One of these days i will.

not that problem..it was the regulators..all 4 of them had some kind of problem

the new one i replaced works fine with no problem

[christos]

guys, my 1A v-reg is blowing up when i try to run 2A through it?

boy, that one is a mystery.

i believe i have seen at least 5 posts here recommending to read the data sheet.

78xx series datasheet:

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

why shoud i not read the datasheet..i did it many times..the regulators was the problem..all four of them died in 1 sec
..bought a new one from another e-shop and it works fine

[lewis]

Fake parts = false economy

[Monkeh]

guys, my 1A v-reg is blowing up when i try to run 2A through it?

boy, that one is a mystery.

i believe i have seen at least 5 posts here recommending to read the data sheet.

78xx series datasheet:

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

why shoud i not read the datasheet..i did it many times..

But you show no signs of having absorbed any of the information in it.

[christos]

guys, my 1A v-reg is blowing up when i try to run 2A through it?

boy, that one is a mystery.

i believe i have seen at least 5 posts here recommending to read the data sheet.

78xx series datasheet:

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

why shoud i not read the datasheet..i did it many times..

But you show no signs of having absorbed any of the information in it.

  i knew that the problem was from the regulators from the Reply #34..i didnt know that there was chinese regulators...but why shoud a 7805 work in the same pcb and not the 7808 at 10 volts dc...i tried difrent value of volts and the same thing ..all burnd out..anyway..thx for the help..i did learn something from the replays about the diode and the most important to know what to buy..  second mistake i made without realizing what im buying and spending money for nothing..the first mistake was when i bought a micro sd 32GB and the second day my phone didnt reconize it cuz it went to 8MB from 32GB

[christos]

and one more question..in this forum, do i have any list of firnds? can i add friends?  if yes then let me know and when my frind comes to greece ill ask him the short circuit protection with only 2 or 3 hight values resistors..still trying to figure how he did it

[Zero999]

  i knew that the problem was from the regulators from the Reply #34..i didnt know that there was chinese regulators...but why shoud a 7805 work in the same pcb and not the 7808 at 10 volts dc...i tried difrent value of volts and the same thing ..all burnd out..anyway..thx for the help..i did learn something from the replays about the diode and the most important to know what to buy..  second mistake i made without realizing what im buying and spending money for nothing..the first mistake was when i bought a micro sd 32GB and the second day my phone didnt reconize it cuz it went to 8MB from 32GB

If the circuit has a constant resistance, more current will flow with an 8V regulator than a 5V regulator so that might be your problem.

[christos]

  i knew that the problem was from the regulators from the Reply #34..i didnt know that there was chinese regulators...but why shoud a 7805 work in the same pcb and not the 7808 at 10 volts dc...i tried difrent value of volts and the same thing ..all burnd out..anyway..thx for the help..i did learn something from the replays about the diode and the most important to know what to buy..  second mistake i made without realizing what im buying and spending money for nothing..the first mistake was when i bought a micro sd 32GB and the second day my phone didnt reconize it cuz it went to 8MB from 32GB

If the circuit has a constant resistance, more current will flow with an 8V regulator than a 5V regulator so that might be your problem.

then how do you explain when i replaced the new ones, the regulator works fine and still works?

[lapm]

  i knew that the problem was from the regulators from the Reply #34..i didnt know that there was chinese regulators...but why shoud a 7805 work in the same pcb and not the 7808 at 10 volts dc...i tried difrent value of volts and the same thing ..all burnd out..anyway..thx for the help..i did learn something from the replays about the diode and the most important to know what to buy..  second mistake i made without realizing what im buying and spending money for nothing..the first mistake was when i bought a micro sd 32GB and the second day my phone didnt reconize it cuz it went to 8MB from 32GB

If the circuit has a constant resistance, more current will flow with an 8V regulator than a 5V regulator so that might be your problem.

then how do you explain when i replaced the new ones, the regulator works fine and still works?

Well hard for us to say exactly what was wrong in your circuit. We have to rely only to information you have provided. I am glad you finally got it working.

Your last comment how ever seems to verify that this is either case of fake Chinese parts (Bossibly with alternative pinout) or you had short circuit there causing massive overload and removed it while changing components, maybe without even realizing it being there.

[christos]

  i knew that the problem was from the regulators from the Reply #34..i didnt know that there was chinese regulators...but why shoud a 7805 work in the same pcb and not the 7808 at 10 volts dc...i tried difrent value of volts and the same thing ..all burnd out..anyway..thx for the help..i did learn something from the replays about the diode and the most important to know what to buy..  second mistake i made without realizing what im buying and spending money for nothing..the first mistake was when i bought a micro sd 32GB and the second day my phone didnt reconize it cuz it went to 8MB from 32GB

If the circuit has a constant resistance, more current will flow with an 8V regulator than a 5V regulator so that might be your problem.

then how do you explain when i replaced the new ones, the regulator works fine and still works?

Well hard for us to say exactly what was wrong in your circuit. We have to rely only to information you have provided. I am glad you finally got it working.

Your last comment how ever seems to verify that this is either case of fake Chinese parts (Bossibly with alternative pinout) or you had short circuit there causing massive overload and removed it while changing components, maybe without even realizing it being there.

what i did was 1)cut the power of 2)remove the regulator 3)clear the solder that was left 4)place the new one            5) solder it so it shines 6)make a continuity test if there was a problem ..i did that 4 times and the 5th time it worked