# Center tap transformer. Voltages 180 out of phase but what about direction of current in 2 parts?

In the center tap transformer (attached picture), my understanding is that volatges in 2 parts in secondary coil would be 180 out of phase. I want to understand the direction of current in both the parts. Will the direction of current in Part 11 would be same as Part 1.? If yes how does that reconcile with voltages being out of phase by 180 in both the parts.?

• Yes it would. To reconcile it, in both R1 and R2, the top of the resistor is +ve (at the instant you drew the circuit) so the current through them is in the same direction. May 21 at 13:34

In the center tap transformer ... volages in two parts in secondary coil would be 180° out of phase.

Yes, but only because you have set the GND reference on the centre-tap.

simulate this circuit – Schematic created using CircuitLab

Figure 1.

I want to understand the direction of current in both the parts. Will the direction of current in Part 11 would be same as Part 1?

• The voltages are actually in-phase as shown in Figure 1.
• In both circuits the current is flowing clockwise.
• If V1 = V2 and R1 = R2 then I1 = I2 and the current in the centre-tap = 0.

simulate this circuit

Figure 2. (a) It may be clearer how V1 and V2 are in phase if we use the bottom tap as our GND reference. (b) Even if we use the top tap as GND reference it doesn't change the voltage or currents.

Figure 3. Voltages at one instant (90°) on the original sketch.

• Note that V1 is positive. That means the voltage at the top of R1 (1) is higher than at the bottom (3).
• Note that V2 is negative. This means the voltage at the top of R2 (3) is higher than at the bottom (2).
• Both voltages are in the same direction. They are in phase.
• It's only when you change your reference point to the centre-tap that they appear out of phase.
• why are voltages in phase in Figure 1 @Transistor ? it seems to be center tapped too.? May 21 at 13:01
• @user, because the voltage is increasing from bottom to top. The bottom tap is the lowest voltage at the instant I've drawn it, the upper is the highest and the centre-half is midway between. The two halves are in-phase a drawn. Measuring from the centre-tap makes them appear out of phase. May 21 at 14:14

The current in R1 and R2 will be parallel, i.e. while the conduction on one side will be "out of" GND, the conduction on the other side will be "into" GND.

The voltage between node "+" and "0" $$\V_{+,0}\$$ is the same as $$\V_{0,-}\$$. Therefore, the current through the resistors has to be the same too (for identical resistors).

• currents through R1 and R2 flow simultaneous @tobalt ? May 21 at 13:03
• @user31058 yes they do flow at the same time in the same direciton May 21 at 14:09
• thx @tobalt so if they are flowing at the same time in same direction how does that reconcile with voltages 180 out of phase in both parts.? is there an connection between current directions and voltages being out of phase in those 2 parts.? May 21 at 14:13
• @user31058 current flowing in the same direction means voltage drops in the same direction, which is what you have drawn too: V+ -> (drop down) -> GND -> (drop down) -> V- May 21 at 14:18