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In transformer schematics you will see dots marking the polarity of one coil with regard to other. For a long time I was thinking when one dot end is positive, other dot end should always be positive. But you need to remember that this dot relationship is always maintained with regard to induced voltage, but this induced voltage is sometimes masked by the supply voltage. As you can see, this circuit sometimes does not follow dot relationship with regard to polarity. In this circuit, (turn the switch on and wait for about 30 seconds untill secondary side voltage drops to about 0.5v) when you repeatedly turn the switch on and off, you will see that at the primary side voltage changes from about 0.2V to 1V while in secondary it is between anout -0.3 to 0.5V. While doing this if you consider the switch off state, primary voltage is about +0.2V while secondary voltage is -0.3V (so, polarity in the secondary is in reverse direction compared to 'dot' relationship). But to see this you must carefully select the resistor value and transformer inductance. Otherwise it can not be seen due to the induced negative voltage in primary. I'm unable to mark dots in the circuit. Consider as the two upper ends are maked with dots.
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