# How to find measured value of voltage using primary and secondary voltages?

#### gbtbtbt

Joined Mar 18, 2020
70
If you have given values of the primary voltage and secondary voltages,

1.) How do you determine if the voltage is boost or buck with given EP and ES?
2.) How do you find the measured value of voltage with both primary and secondary voltage?

Joined Jul 18, 2013
23,342
It is only Buck or Boost whichever two conductors, one on each of the primary and secondary, are used as the common reference.
Look up the circuit of a typical buck-boost transformer diagram.
The secondary voltage value will either add to, or subtract from the primary, dependent on which of the two connections are selected, Buck or Boost!!
Max.

#### gbtbtbt

Joined Mar 18, 2020
70
do you not just add or subtract depending on whether the secondary voltage is lower or higher than the primary voltage? If the secondary voltage is higher, would you add both voltages together and when secondary voltage is less than primary, would you then subtract both voltages?

#### ronsimpson

Joined Oct 7, 2019
1,312
How do you
It would help if you gave an example of what you are thinking of. (schematic) There are too many ways of using a transformer.

Joined Jul 18, 2013
23,342
do you not just add or subtract depending on whether the secondary voltage is lower or higher than the primary voltage? If the secondary voltage is higher, would you add both voltages together and when secondary voltage is less than primary, would you then subtract both voltages?
There is no unique, buck or boost transformer, just combined buck-boost and the result all depends on the phase of the buck/boost winding WRT to the voltage of the supply transformer it is acting on.
Max.

#### DickCappels

Joined Aug 21, 2008
7,540
I am going to make a guess: gbtbtb is asking about simple AC transformers, such as a filament transformer as one might use to power a small project, but is using terms that we associate with switching power supplies. Hence, the confusion.

@gbtbtbt are you talking about an old fashioned transformer or a switching power supply?

#### Alec_t

Joined Sep 17, 2013
12,148
I think this TS's thread is related to his other one, which involves a simple old-school transformer with only two windings.

#### gbtbtbt

Joined Mar 18, 2020
70
We used a fully protected transformer from the brand Lab Volt. It looks like a relatively simple transformer, fitted with three discrete windings. As well I was told that to find boost or buck connections depends on which is greater Ep or Es. If Ep is bigger than you would subtract with Es, however, if Es is bigger than you would add with Ep.