# Power supply able to reach 0V - what for?

#### atferrari

Joined Jan 6, 2004
4,122
It is frequent reading someone extolling the capability of a PSU 's output to reach down to 0V. While it could be reasonable to have a minimum output of maybe 1V, or even 0,5V (guessing here), why 0? What for?

Assuming the common in a circuit is 0V, the output now in 0V, how equal is it to that common, on account of all the electronics in the middle, allowing me to reach that value?

Most of the common lab PSUs are not able to sink current and, at 0V why could be it different?

#### shortbus

Joined Sep 30, 2009
8,057
It is frequent reading someone extolling the capability of a PSU 's output to reach down to 0V.
I found a way to do it and will sell them to anyone wanting one. Going to patent it too. hope no one is listening, here's the secret, cut the plug off of the power supply. Instant 0V supply.

#### crutschow

Joined Mar 14, 2008
25,686
While it could be reasonable to have a minimum output of maybe 1V, or even 0,5V (guessing here), why 0? What for?
About the only reason I can think of is if you wanted to connect a diode across the output so you could test the forward characteristics down to a low voltage.

The LM317 has a minimum output of 1.25V, and it is often used to make a simple bench supply.
As you imply, a supply voltage below that value is seldom needed.

#### atferrari

Joined Jan 6, 2004
4,122
About the only reason I can think of is if you wanted to connect a diode across the output so you could test the forward characteristics down to a low voltage.

The LM317 has a minimum output of 1.25V, and it is often used to make a simple bench supply.
As you imply, a supply voltage below that value is seldom needed.
But, you see, LT took the pain to create a linear regulator 0V able.

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#### dl324

Joined Mar 30, 2015
11,926
I designed a power supply for an EPROM programmer that can switch the VCC and VPP voltage applied to the EPROM to 0V. It's controlled by a program that sets the voltages according to the operation being performed. After reading and/or programming, the supplies are set to 0V so the device can be removed from the socket.

#### Papabravo

Joined Feb 24, 2006
14,701
My guess is that this was not a requirement until devices with Vcc at less than 1 VDC appeared on the market. The reason for that was a power dissipation term that was a function of (Vcc)².

#### Papabravo

Joined Feb 24, 2006
14,701
@dl324 Good point about the programming voltages. There is a big difference between a supply at 0V output and one that is just off.