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I am using the following flyback transformer from Pulse electronics:

enter image description here

I am typically used to seeing the dots reversed on the diagram. For this transformer, would current be flowing out of pins 5, 9 and 6?

Additionally, if I shorted pins 10 + 7, and 9 + 6, can I effectively double my output current to 4.5A for a single output?

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  • \$\begingroup\$ on every second half-cycle ... yes \$\endgroup\$
    – jsotola
    Jan 16, 2023 at 2:28
  • \$\begingroup\$ would current be flowing out of pins 5, 9 and 6? <-- it depends entirely on the circuit connected to pins 1 and 2. \$\endgroup\$
    – Andy aka
    Jan 16, 2023 at 10:37
  • \$\begingroup\$ @jsotola If this was a forward converter, yes. With a flyback, I wonder if flowing out is to imply current direction/voltage polarity. \$\endgroup\$
    – greybeard
    Jan 16, 2023 at 18:45

2 Answers 2

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Yes, but make sure the output rectifier conducts when the primary transistor is blocked, NOT at the same time. And yes, if the two 5V secondaries are identical, you can parallel them with no problem. In case of doubt about the phases, measure the primary inductance before and after interconnecting the secondaries. If you made a mistake, inductance will plummet.

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Additionally, if I shorted pins 10 + 7, and 9 + 6, can I effectively double my output current to 4.5A for a single output?

In a flyback circuit, the secondary output power is determined by the energy stored in the magnetic field during the first part of the switching cycle. When it comes to the 2nd part of the switching cycle, the stored magnetic energy is transferred to the secondary. This means that no amount of parallel secondary windings will increase the current available for the load.

The answer is therefore no.

For this transformer, would current be flowing out of pins 5, 9 and 6

If the primary pin 1 is connected to the incoming DC supply positive line and a MOSFET is used as a switch between pin 3 and ground then, you could use pin 5, 9 or 6 as the connection to the anode of the series output diode and, current would flow into the load on the 2nd part of the switching cycle.

Can you change the polarity of a flyback transformer by swapping the output pins?

Given that flyback converters are generally used to provide galvanic isolation between an AC source and the DC output. You can use the floating DC output as a negative supply (with respect to 0 volts) or, as a positive supply.

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