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About transformers, can any type of transformer lower voltage without simultaneously raising current??

I understand that transformers used to lower voltage for AC power transmission, simultaneously change both the voltage and current, but if such a transformer were in used in say a 12 volt dc power adapter that plugged into the wall outlet, then it would be counterproductive if the voltage lowering transformer upped the current as too much power would be dissipated, and a current boost would be unwanted, right? Same with transformer for PC power supplies. They must lower voltage without upping the current, right? Thanks a lot.


transformers work only when the input is AC not DC after the out put is obtained then the AC is converted to DC by rectifier. however the process of change would have already taken place in the main sequence whatsoever the rectifier does. in small amounts of current the change would be negligible
For a perfectly efficient (100% efficiency) transformer, [Power before transforming] [Power after transforming] That is V1 I1 V2 I2 Therefore, it DOES up the current when lowering the voltage. However, for a transformer that is not 100% efficient: [Power before transforming] [efficiency in %age]/100) × [Power after transforming] Therefore, for a non-efficient transformer, it is theoretically possible to lower the voltage without upping current. For example for a 50% efficient transformer thet converts 220 V ac at 20A to 110 V: 220 × 20 (50/100) × 110 × x Solve for x: x 20A
Transformers are power transmission devices. For a given load and turns ratio, a transformer will convert the input voltage and output voltage per the turns ratio. The current is determined by the load, not the transformer. This current is then transferred to the primary per the turns ratio. For example, if you have a 10:1 transformer that converts 120VAC to 12VAC, but there is no load connected, the current will be zero. So, while you still measure 12V at the secondary, no current can flow because there is nothing connected. If you connect a 1A load, the current at the primary will be one tenth or 0.1A. Thus, the power at the primary (120V * 0.1A) is equal to the power at the secondary (12V * 1A) or 12 watts. Of course, real transformers have losses, so the currents won't come out exact since a small amount of power is lost in the core of the transformer. Exactly how much power loss ocurrs depends on the construction of the transformer. So, transformers convert the primary voltage per the turns ratio, and the secondary current is transformed in the other direction.
You have a major misconception. The amount of current out of a transformer is determined by the load. The transformer sets the MAXIMUM current available, but the actual current is determined by the load placed on the transformer. So if you plug a transformer into 120 VAC to get 5 volts AC for a PC, even though the 120 volt AC outlet is rated at 20 amps, that does not mean you get 20*60 amps out of the transformer. The maximum current out of the transformer in the above example is set by the rating on the transformer, say 10 amps, not 1200 amps. And the actual current that flows out of the transformer is determined by the load. Open circuit, it is zero. Connected to its load, it could be 5 amps. And this is where the current ratio comes into play. that 5 amps causes 5/60 or 0.083 amps in the primary. to elaborate further, a 12 volt battery has a 100 amp capability. That means the battery can put out UP TO 100 amps. But the actual current drawn by the battery depends on the load.

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