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Protecting a regulator

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quickrik

New Member
Hi

I have a simple circuit involving an LM7805 to get the a 12v feed down to 5v to drive a pic. I've had a couple of people blow the regulator up by connecting it up backward. Is there a simple circuit I could use that would protect the regulator burning out if it was accidently wired up backwards?

Rik
 

ericgibbs

Well-Known Member
Most Helpful Member
quickrik said:
Hi

I have a simple circuit involving an LM7805 to get the a 12v feed down to 5v to drive a pic. I've had a couple of people blow the regulator up by connecting it up backward. Is there a simple circuit I could use that would protect the regulator burning out if it was accidently wired up backwards?

Rik
hi,
Are you saying the 7805 is being wired 'backwards' or that somehow you are putting a negative voltage on the 7805 or getting the 0V and +5V lines reversed to the load.:confused:
 

eblc1388

Active Member
No. Components will be destroyed if wired up wrongly.

You can simply provide them with a large, clear connection diagram or photo on how to place/connect the 7805 regulator to the rest of the circuit.
 

Styx

Active Member
put a rectifier between the 12V and the regulator that way if they are that stupid it still works \o/

that or put a diode so if they are stupid it won't work but wont get destroyed
 

audioguru

Well-Known Member
Most Helpful Member
It is called an "idiot" diode.
Sometimes a big diode is connected across the supply to blow a fuse if the power is connected backwards.
 

quickrik

New Member
No dispite labeling the wires and giving clear instructions. People still manage to reverse the wires, I guess you can make any assumptions about people with consumer electronics.

So would just a simple diode in series on the input side of the regulator be enough to protect my circuit then?
 

ericgibbs

Well-Known Member
Most Helpful Member
quickrik said:
No dispite labeling the wires and giving clear instructions. People still manage to reverse the wires, I guess you can make any assumptions about people with consumer electronics.

So would just a simple diode in series on the input side of the regulator be enough to protect my circuit then?
hi,
No!.:eek:

If the assembler is inserting the 7805 the wrong way round in the pcb mounting holes, there is little you can do to fully protect the device!
 

audioguru

Well-Known Member
Most Helpful Member
quickrik said:
So would just a simple diode in series on the input side of the regulator be enough to protect my circuit then?
Of course. The diode won't conduct if the power supply polarity is backwards.
 

Hero999

Banned
They could connect the output to 12V instead of the input.

There could be 80V transients on the 12V line that would overvoltage the regulator.
 

Styx

Active Member
"they" could do alot of things.

the magic diode is only really good for most end-user stupidity. Design/Construction stupidity needs to be plugged into an non-earth appliance and irradicate it from the gene-pool (well we all make mistakes so maybe not straight away ;) )
 
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