confused about voltage regulator spec

[ImperialGuardWH40K]

Hello,

 

[hotwaterwizard2]

A part number would help.
The answer to your question:
One rating is with a heat sink and the lower is without a heatsink.

Here is the datasheet.

http://www.jameco.com/wcsstore/Jameco/Products/ProdDS/51246.pdf

 

[audioguru2]

You can buy a lot of voltage regulators. 7805 is 5V, 7809 is 9V, 7812 is 12V and 7815 is 15V.
You can buy them in a small plastic case and their max current is 100mA or a larger TO-220 case that can be bolted to a heatsink and their max current is 500mA and 1A.

Current in a load resistor changes proportionally with voltage.
A voltage regulator can supply as much current as it is made for.

 

[Theatronics]

Remember your basics.

P = E * I.
If the Voltage into the chip is 9V and the voltage out is 5 then there is a 4V drop across the part.
If the current flowing is 250ma then the wattage being expended at that part is
250ma * 4V = 1W

If you drop that part in Liquid N (Assuming it can operate at that temp)
You would get a MUCH higher Wattage beause the heat wouldn't melt the part down.

Current carrying capicity is really all about how much HEAT a part can handle or get rid of.  High current parts are usually large because they need to sink more heat.

-Mike

 

[Theatronics]

close,
I think they just put the same part in a cheaper package.

there is no differance between a 7805 in a TO-220 case or a TO-92 case.
They are the exact same die.  But the smaller TO-92 case will pop like
a firecracker if you try to pull 2 amps through it.

-Mike

 

[audioguru2]

I think they just put the same part in a cheaper package.

there is no differance between a 7805 in a TO-220 case or a TO-92 case.
They are the exact same die.View attachment 39343

 

[Theatronics]

I've blown them up.
magic smoke escaped, parts flew, blown up.
That protection stuff works for well designed circuits.
when you just plain abuse them, they go poof.

-Mike

 

[audioguru2]

You can overload or short the output of a regulator. It will limit the current, get hotter and hotter and if the heatsink isn't big enough then the regulator will shut down. After it cools it will begin working again.

It isn't recommended to leave a regulator cycling like that because of the thermal stress of it heating and cooling so many times.

 

[Theatronics]

Just in case you wondered.
The inside of a 7805 looks like this.
(Sort of).

Depends on the manufacturer.

-Mike

View attachment 39345

 

[ante1]

I've blown them up.
magic smoke escaped, parts flew, blown up.
That protection stuff works for well designed circuits.
when you just plain abuse them, they go poof.

-Mike

There is at least one way to do this; reverse the polarity on the output! Example; put a charged capacitor the wrong way across the output!
Use safety goggles for this one! 8)

 

[indulis]

The die will be the same, only the current limit point will be trimmed (laser) to a different point. The carrier size is for heat.

 

[c3r14l.k1l4]

How is it that 5 volts could output 250mA and 1 amp?

Because those devices are current limited (it's like they have resistors in series inside them). They wont give you more current for the purpose of not exceeding the maximum rating power (humm, burn ).

 

[indulis]

That is correct, they do have resisistors inside of them that are trimmed with lasers when the wafer is being tested. BTW- there are capacitors in there too, and some even have inductors.