dc voltage to a transformer

[dinesh401]

what happens if we give 120v DC to a 120/12v transformer. can i get 12v DC output ?

 

[jeffrey samuel]

No chance to step down DC voltage there are special ckts called DC DC converters

IF you want to use a transfo then you need to invert the DC signal into AC and then step it down and then regulate it to the required voltage

 

[Tahmid]

When you give DC input, the transformer winding acts like a resistance and you get a short circuit. Transformers function only with AC signal or pulsating DC.

 

[jeffrey samuel]

the reason for pulsating DC response is cos of the fact of presence of AC ripples in the DC signal

 

[dinesh401]

When you give DC input, the transformer winding acts like a resistance and you get a short circuit. Transformers function only with AC signal or pulsating DC.

normally if you in case of relay. we will ON the relay by passing DC through it then it will produce magnetic field and then it will operate. The relay is also having a coil producing magnetic flux.

 

[Tahmid]

normally if you in case of relay. we will ON the relay by passing DC through it then it will produce magnetic field and then it will operate. The relay is also having a coil producing magnetic flux.

In the case of transformer, EMF must be induced in the secondary. For that a changing magnetic field is required as the secondary coil is fixed. DC can provide magnetic field, but not a changing one. In case of relay, you don't need a changing magnetic field.

 

[dinesh401]

In the case of transformer, EMF must be induced in the secondary. For that a changing magnetic field is required as the secondary coil is fixed. DC can provide magnetic field, but not a changing one. In case of relay, you don't need a changing magnetic field.

that means if we place an inductor in a constant magnetic field ..we won't get any voltage...Is it right ?

 

[FvM]

that means if we place an inductor in a constant magnetic field ..we won't get any voltage...Is it right ?

That's a mandatory conclusion from the differential operator in Faraday's law.

https://en.wikipedia.org/wiki/Electromagnetic_induction

 

[albert22]

As Tahmid said if you put DC into a transformer it presents a very low resistance. Virtually a short circuit. Then you will fry the thing.
The winding of a relay is designed to have enough resistance to limit the current flowing. And to produce a constant magnetic field to attract a piece of iron which closes (or opens contacts).
Either a moving coil or a variable magnetic field is required to induce a voltage.
Think of a dynamo or your cars alternator. They dont work if not rotate, right ?

 

[jeffrey samuel]

yeah true the differential voltage needs the actual voltage to vary with the reference plane which is the time domain

So if the voltage does not vary with time ( in case of DC ) there no probability of varying flux be produced

varying flux is needed in a transformer for induction of voltage in the secondary

 

[fredd]

what happens if we give 120v DC to a 120/12v transformer. can i get 12v DC output ?

you can just build a dc-dc converter/transformer through voltage divider using resistor network or diode network.

 

[vimalkhanna]

If you need 12VDC from a 120VDC ,why use the transformer ??Use a three pin 12V DC regulator/or a 12V zener reference instead with a series regulator like a 2N 3055 /better ...What is the current ratings of the 12VDC required by you .??

 

[albert22]

Three terminal regulators cannot withstand an input voltage of 120V. The 2N3055 max VCEO is 100V, will not work either.
A zener can be used for very low current output but with poor efficiency because power disipated will be high. Any other type of linear regulator will have similar problems. Because of the great dropout (108v).
A switching step-down or "buck" DC to DC converter is the best way.