LM317 no reference voltage

AnalogKid said:

Incorrect. There is no maximum input voltage (to GND) specified for the LM317. There is a maximum input-output differential voltage spec of 40 V. This is the voltage from the Vin pin to the Vout pin, *not* from the Vin pin to GND. The unique (at the time) characteristic of the 317 is that it has no GND connection; it "floats" in the shunt adjustment resistor. For example, if the input voltage is 370 Vdc, and the output voltage is 350 Vdc, the chip will be perfectly happy.

ak

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True, it is the Vi-Vo maximum that is 40V. However, if his Adjust tried to set output voltage to a low value, like 5V, then with 48V input, he would have exceeded that limit. We just don't know how he ran that circuit at all times. If his 10k pot was set to zero ohms, there could have been issues. No one should be putting 48V as input until they know the circuit is working properly in the first place. I've run LM337 as an adjustable negative regulator in the -65V to -95V range with proper bias zener diode on the Adjust pin to ground, so I know it can be done, but I also knew the circuit was working in the first place before putting -100V on the input