±45v lm317?

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hello,i need ±45v power,i get i picture on the internet ,but i do not know it is right or not ,who can help me ?
An externally hosted image should be here but it was not working when we last tested it.

Easy. The voltage across R1 is ALWAYS 1.25V. So if you want to know the output voltage, you select the total of Vr1 + R2 to add voltage to the 1.25V.
An example: for output of 11.25V, you know that there will be 10V across R2+Rv1. (11.25 - 1.25). 10V is 8 times 1.25V on R1 so R2 + Vr1 = 8 times R1 = 8 times 220 = 1720 ohms.

For your 45V you know on R2 + Vr1 is 45-1.25 = 43.75V, so R2 + Vr1 = 43.75/1.25 * 220 = 7.7k....

For the -45 you can use an LM337 but the calculation is the same.

BTW This is also in the datasheet, very simple, you could easily find that yourself without worrying what is true or not. Datasheets are your friend! ;-)

jan didden
 
Last edited:
Easy. The voltage across R1 is ALWAYS 1.25V. So if you want to know the output voltage, you select the total of Vr1 + R2 to add voltage to the 1.25V.
An example: for output of 11.25V, you know that there will be 10V across R2+Rv1. (11.25 - 1.25). 10V is 8 times 1.25V on R1 so R2 + Vr1 = 8 times R1 = 8 times 220 = 1720 ohms.

For your 45V you know on R2 + Vr1 is 45-1.25 = 43.75V, so R2 + Vr1 = 43.75/1.25 * 220 = 7.7k....

For the -45 you can use an LM337 but the calculation is the same.

BTW This is also in the datasheet, very simple, you could easily find that yourself without worrying what is true or not. Datasheets are your friend! ;-)

jan didden



thany you very much ,i see.
 
Beware the input-output voltage limit

For any input voltage above 40V, there's no short circuit protection with this device - I've seen at least one explode, so be very wary of shorting the output. On power-up transients too its possible to exceed the abs max.
 

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