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I Know these symbols mean a transformer step up or down:

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But what does this one represent since it has the same size on both sides?

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Part above taken from this schematic:

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And this also has me confused as what type its using? A small red with a larger blue?:

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This part above is taken from this schematic:

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3 Answers 3

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I wouldn't count on the number of turns or apparent size of the windings on a schematic symbol as having any relation to the actual turns ratio of the real transformer.

From the voltages shown, the transformer in your last drawing is obviously a step-down transformer with several taps on the secondary, although the primary is shown as much smaller than the secondary, which would imply a step-up transformer based on your first drawing.

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    \$\begingroup\$ The transformer in circuit 2 is drawn with a larger secondary just to fit on all the different windings without having them unreadably close together. Circuit diagrams are about conveying information, and here they have to make the secondary bigger to fit it all on. That trumps anything about relative sizes of the windings. \$\endgroup\$
    – user1908704
    Commented Jun 10 at 15:33
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Many people draw the transformer step up and step down to show the relative size of the coils. The size (on the schematic) doesn't necessarily indicate step up or step down, but the coil ratio does, so look for a coil ratio or a voltage indicator on the transformer diagram.

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  • \$\begingroup\$ Thanks for clearing that up. Can you tell me what type of transformer they are using in the schematic on that page? The T1 3A version? eleccircuit.com/wp-content/uploads/2020/06/… \$\endgroup\$
    – StealthRT
    Commented Jun 7 at 23:35
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    \$\begingroup\$ That schematic clearly shows a step-down transformer, despite the relative sizes of the windings. The drawing shows the primary as 117/230 V (not really possible, but probably intended to show that the power supply could be equipped with a transformer suitable for use with either common AC voltage) and secondary with taps to provide 9 and 15 VAC. \$\endgroup\$
    – Peter Bennett
    Commented Jun 8 at 0:24
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An incorrect assumption confused you. You assumed the transformer was step-up or step-down based on what it looked like to you. The answer is staring you in the face. From your two schematics, it is obvious they are step-down transformers. Circuit one is a 117 VAC primary and 15-volt secondary with a 12 and 5-volt output port. It is a poor design. Mr Paul (5-volt port) robs Peter (12-volt port). Series connected.

Circuit 2 is an improved design with a 117 VAC primary and a center—tapped secondary, with 9—and 15-volt output taps for 5—and 12-volt regulators.

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  • \$\begingroup\$ Although a 9 V tap for a 5 V linear regulator seems excessive. Rectified 5 V AC is about 7 V, more than enough to regulate down to 5 V DC even with a cheap linear regulator, and you'll be losing less power to it. Same story with 12 V AC to 17 V rectified, should be enough even to regulate to 15 V DC. \$\endgroup\$
    – Hearth
    Commented Jun 9 at 1:45

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