LM337 subtitute to LM317???

[AMalonzo]

Hello there guys,

I already found a design for 7.5V / 800mA regulated power supply, thanks for everybody who share their knowledge.
But my problem now is that i don't have a LM317 here but instead I have a LM337 at hand. As far as I know LM317 is a positive voltage regulator but LM337 is a negative voltage regultor.
Can I subtitute the LM337 to LM317? What will gonna be my connection, I already have a figure in my mind of the posible connection, but I'm not sure if this will work. And for safety reason I am seeking for an advice for those who is much experienced.
Any reply is higher appreciated.

Regards

 

[Nigel Goodwin]

Hello there guys,

I already found a design for 7.5V / 800mA regulated power supply, thanks for everybody who share their knowledge.
But my problem now is that i don't have a LM317 here but instead I have a LM337 at hand. As far as I know LM317 is a positive voltage regulator but LM337 is a negative voltage regultor.
Can I subtitute the LM337 to LM317? What will gonna be my connection, I already have a figure in my mind of the posible connection, but I'm not sure if this will work. And for safety reason I am seeking for an advice for those who is much experienced.
Any reply is higher appreciated.

You can simply regulate in the negative rail instead, you still end up with a positive and negative. This was commonly done in 12V portable TV's, to regulate the 12V with a low voltage drop.

 

[AMalonzo]

Thanks. Another question, if the value of the two resistor are changed does the ouput current will be affected?

 

[Nigel Goodwin]

Thanks. Another question, if the value of the two resistor are changed does the ouput current will be affected?

No, they just set the voltage.

 

[AMalonzo]

Having a load of 7.5V/800mA, do I need to use a heat sink? what size do i need if ever? My input 12Volts.

 

[Nigel Goodwin]

Having a load of 7.5V/800mA, do I need to use a heat sink? what size do i need if ever? My input 12Volts.

Presumably the datasheet covers heatsink calculations?.

Personally I'd try a reasonable size one to start, and see how hot it gets :lol:

A lot depends if the load is constant, if so it will obviously be runing hot all the time - if it's in a metal case, you may be able to use the case as the heatsink. Again, try it and see how hot it runs.

 

[chir]

Lm337 can replace Lm317

Hey i came to know that u have only Lm337 i have an answer dont neglet it .
It is simple just give +ve terminal of ckt to ground terminal of regulator and -ve terminal to -ve of regulator ( i think it don`t effect u r ckt)

 

[audioguru]

It is simple just give +ve terminal of ckt to ground terminal of regulator and -ve terminal to -ve of regulator ( i think it don`t effect u r ckt)

WRONG!
Look at the circuit on the datasheet of the LM337.
The resistors and capacitors must use the positive supply as ground, not the negative that is used for the LM317.
.

 

[Hero999]

If you're only using it as a single power supply then it won't make any difference so long as the input isn't earth bonded and the appliance attached isn't connected to anything earth bonded.

If it's a bipolar power supply then it will matter, you'll need an LM337.

You can make a bipolar power supply with two LLM217s but you need a transformer with two separate secondaries and two bridge rectifiers and smoothing capacitors.