# regulator ?

Discussion in 'General Electronics Chat' started by Mathematics!, May 14, 2009.

1. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
I am trying to determine which legs of the regulator are what.

They have a picture on the back of the package that say's 1 = Vin , 2 = (Vout tied to tab) , 3 = ADJ.

I am unsure where pin 1 starts?

When I look at the regulator should pin one start at the far right or left?
And which side of the regulator should I be looking at when determining the pins. The side that has the metal plate on it or the side that doesn't have the metal plate (heat sink ) on it?

The characteristics of the regulator are
max ratings
Power dissipation: 15 watts
input-output voltage differential 40 V

I am wondering what the input-output voltage differential 40 V means?
Is it just saying that the difference between the input and output voltage cann't be greater then 40 V?

2. ### bertus Administrator

Apr 5, 2008
15,806
2,389
Hello,

Just take a look at the LM317 datasheet (attached)

Greetings,
Bertus

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3. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Thanks for the pdf.

Great info.

But I am still a little unsure of what package type I have. The on that it looks almost identical with is on page 2 of pdf TO-220(T).

It is radioshack part 276-1778 LM317T adjustable voltage regulator.

When they say front side do they mean the side that the metal is not showing or the metal plated side?

4. ### bertus Administrator

Apr 5, 2008
15,806
2,389
Hello,

The metal plate is the back.
On the inside the chip is mounted.
The metal plate is used to transfer the heat of the chip to the outside.
You can mount the metalplate side to a heatsink.

Greetings,
Bertus

5. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok, So going by looking at the front side of the regulator. The picture on the radioshack package say's
Pin Vin would be all the way to the right.
Pin Vout would be in the middle.
Pin ADJ would be all the way to the left.

6. ### bertus Administrator

Apr 5, 2008
15,806
2,389
Hello,

Correct. The picture says frontview (looking at the plastic side).
Note that the output is connected to the metal part.
This can give trouble when you mount it on a heatsink that is not (electricaly) free from the rest of the circuit.

Greetings,
Bertus

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7. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok so my circuit is working good with the regulator.
But I am wondering. if this bridge retifier would with stand 90 volts AC at 20 Hz?

It say's that working peak voltage is 100 V and RMS is 70 volts max ratings at TA=77degs F
Peak surge current 50 A 8.3ms , nonreps

DC forward current at TA= 140deg F 1500mA = 1.5A

I am working with input of 90 V ac 20 hz or 50 v DC . I am wondering if this retifier will be OK. 90 rms is pretty close to 70 rms.

I know I am cutting it close. But the AC is very infrequent

Thanks for the help with the regulator I am all set with that.

8. ### mauro.laurenti Active Member

May 8, 2009
68
0
...the 90V measured with the multimeter are

90*1.41 = 126 Vpeak

...don't connect the regulator to 90V AC!

...or the problem will be to find the pins again...
...on the floor!

Ciao,

Mauro

9. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
The maximum voltage would only be exceeded by 28%. It might last through one or two rings before melting.

10. ### StayatHomeElectronics Well-Known Member

Sep 25, 2008
864
40
50V dc with infrequent 90V ac at 20 Hz, almost sounds like you are hooking it up to the phone line.

May 16, 2005
5,072
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12. ### StayatHomeElectronics Well-Known Member

Sep 25, 2008
864
40
People have been doing this kind of thing for years. And, phone companies have been dealing with this for years as well.

It is definitely not recommended.

13. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok, if it's going to blow then what happens if I dropped the voltage to 70 or less before the bridge rectifier with some resistors? Then would I be ok?

14. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
If you wish dependable power, get or make a power supply.

If you want to pay a fine, steal power from the phone company.

15. ### StayatHomeElectronics Well-Known Member

Sep 25, 2008
864
40
If you're lucky, it may stop your phone from ringing at all. Ringing voltage is often times 90Vac superimposed on the -48Vdc battery.