Reference article and paragraph: Relays, Selection & Usage (Part 1) - 8 - Latching Relays
Below are two simplified circuits of dual-coil (A) and single coil (B) latching relay drivers. As is readily apparent, the dual coil version is far simpler, and just uses a transistor to connect one side of the coil or the other to ground to set or reset the relay. The two transistors should never be turned on at the same time because the relay state will be indeterminate when power is removed. Otherwise, no harm is done. Note the way the diodes are connected - this only works if the coil and drive transistors are connected as shown, and the peak voltage across the transistor that remains off is three times the supply voltage (3 x 12V or 36V in this case).
My question is: how in circuit A the voltage reaches 36V across Q2? from the diagram I thought recognize that the voltage potential on each end of the transformer will create a 24V potential difference, but I don't recognize where the other 12V potential comes from.
