Converting voltages using LM337

Thread Starter

Oussama Zaidi

Joined Mar 1, 2016
53
Hi
I have 2 questions:
Is it possible to generate -35V from LM337 regulator with -12V in input??
The voltage output from LM337 is supposed to follow this equation, -Vout=-1.25(1+R2/R1)+Iadj.R2 but in ISIS simulation the output value is always the same as the input, I don't understand why, for example in the picture above output value is supposed to be -32V according to the resistances values but it is -39V because the input is -40V, the same for any other voltage.
LM337.PNG
 

AnalogKid

Joined Aug 1, 2013
8,536
Is it possible to generate -35V from LM337 regulator with -12V in input??
No.

Besides the schematic error, that is not how a linear regulator functions. Basically, it acts like an automatic attenuator. So the equation is correct as long as the output is less than the input. With a -12 V input, the maximum output is around -10 V. This is because the device needs a minimum of 2 volts or so (the exact number is on the datasheet) for it to function.

Some switching regulator circuits can do what you want, but linear regulators sannot.

ak
 

Thread Starter

Oussama Zaidi

Joined Mar 1, 2016
53
No.

Besides the schematic error, that is not how a linear regulator functions. Basically, it acts like an automatic attenuator. So the equation is correct as long as the output is less than the input. With a -12 V input, the maximum output is around -10 V. This is because the device needs a minimum of 2 volts or so (the exact number is on the datasheet) for it to function.

Some switching regulator circuits can do what you want, but linear regulators sannot.

ak
@AnalogKid Can you give me some names of switching regulators can do the job, I do my research but I didn't found any, just anything can give lower than -30V.
 
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