# Buck Boost Converter Questions

#### ben sorenson

Joined Feb 28, 2022
160
Hello, if you have a buck boost conv with a source of 20v DC (Battery) with an output of 90V. Instead of running the load from the pos/neg side of the output could you run the load from the pos output to the positive of the source (battery) because the output of the pos on the buck boost is at a higher potential than the pos on the batt?

#### DickCappels

Joined Aug 21, 2008
10,102
Yes, you can do all those combinations.

#### ben sorenson

Joined Feb 28, 2022
160
Yes, you can do all those combinations.
Is there any benefit from running the output of the boost to the pos on the battery vs just running the load from the pos/neg side of the output? It is a non isolated buck boost conv

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#### Ian0

Joined Aug 7, 2020
8,938
Hello, if you have a buck boost conv with a source of 20v DC (Battery) with an output of 90V. Instead of running the load from the pos/neg side of the output could you run the load from the pos output to the positive of the source (battery) because the output of the pos on the buck boost is at a higher potential than the pos on the batt?
A buck-boost gives a negative output voltage. The positive of the output is common with the negative of the input.
If you connect between the positive output and the positive input, you just have your battery voltage.
 Unless you mean the four-switch buck-boost, and that gives a positive output voltage. If you connect between the output positive and input positive then it will subtract the input voltage, leaving you 70V.

#### LowQCab

Joined Nov 6, 2012
3,560
If You are using a Power-Supply that is nominally ~20-Volts, to obtain ~90-Volts,
You would use a "Boost-Converter", the "Buck" function would not ever come into play.

Since You are increasing the Voltage by more than 4X,
it would be more efficient to use a "Push-Pull" Transformer-based Power-Supply.
The Push-Pull design may be more expensive,
but it is also more stable, and produces less unwanted noise.

It would also have the bonus of an Isolated-Output.
.
.
.

#### ben sorenson

Joined Feb 28, 2022
160
A buck-boost gives a negative output voltage. The positive of the output is common with the negative of the input.
If you connect between the positive output and the positive input, you just have your battery voltage.
 Unless you mean the four-switch buck-boost, and that gives a positive output voltage. If you connect between the output positive and input positive then it will subtract the input voltage, leaving you 70V.
I'm sorry, I am just talking about a non isolated boost converter. Yes, when I measure from the pos output to the pos batt term I do get 70 volts when I have the converter set to 90 +/-.

Just wondering what the difference would be other than the obvious 20V drop when running a load from the pos out to the pos batt term vs. Just from the pos/neg output of the conv.

#### Ian0

Joined Aug 7, 2020
8,938
It works either way.
If you examine the buck-boost circuit, it is identical to a boost converter, but with the load returned to a different supply.