How do electronics (like transformers) convert high voltage, low current to low voltage, high current, and vice versa?

Question

I am fairly new to tinkering with electronics/electronic-adjacent ideas and I have been wondering: how do electronics get the desired voltage/current to operate properly? I understand in AC power, there are step-up and step-down transformers that allow you to raise or lower voltage, but what about the current? The additional voltage can't come out of nowhere due to thermodynamics, so does it convert the current into voltage? And does that work in the opposite way?

So, for instance, say you had a power source of 12 watts (24 volts, 0.5 amps) and you had a device that needs 2 amps. Would a transformer essentially convert the (24 volts, 0.5 amps) to (6 volts, 2 amps)?

Alternatively, if you had a power source of 12 watts (6 volts, 2 amps) and a device that needs (24 volts, 0.5 amps), would a transformer essentially convert the (6 volts, 2 amps) to (24 volts, 0.5 amps)?

I understand conversions would have losses, but these are just hypothetical examples.

If I am mistaking how transformers work, what electrical components and/or circuits can accomplish the functionality stated above?

Answer 1

It's Faraday's law:

Whenever the flux linked or associated with a circuit changes, a voltage is induced in the circuit.

Primary side creates a alternating flux in iron core. Core connects flux to secondary side. A voltage gets induced on secondary side. The voltage on the secondary side depends on turns ratio between primary and secondary.

A transformer cannot transform power. To get 100kVA out of an ideal transformer, 100kVA must go in.

$$S_1 = S_2$$ $$V_1 I_1 = V_2 I_2$$ $$\frac {V_1} {V_2} = \frac {I_2} {I_1} $$ $$\alpha = \frac {V_1} {V_2} = \frac {N_1} {N_2} = \frac {I_2} {I_1} $$

An \$\alpha\$ < 1 is a step-up, \$\alpha\$ > 1 is a step-down and \$\alpha\$ = 1 is an isolation transformer. This refers to the impact on the voltages, because the impact on currents will be opposite.

A step-up transformer steps up voltage, but steps down current.

Answer 2

Transformers handle power (voltage times current) not just voltage or just current.

The power drawn from an AC supply by a transformer will equal the power delivered to a load by the transformer (plus a little due to losses in the transformer).

If the transformer steps the voltage down, it will step the current up by the same ratio.

Answer 3

See Wikipedia Transformers article

The law of conservation of energy means that the real/reactive/apparent power must be the same on both sides (ignoring losses), so that the total power S on the primary side, I_pV_p (also known as watts) equals the power on the secondary side, I_sV_s, such that

S = I_pV_p = I_sV_s

This formula also shows you how changing V_p to V_s affects I_p and I_s inversely. So if you have 12 watts in at 6 volts, V = (6)(2) = I_sV_s and a 1:2 ratio, V_s being 12, I_s must be half to satisfy this formula.