# Q & A: DC input to a transformer?

Q:
what will happen if we provide DC to the transformer in stead of AC?
- jasjit singh (age 22)
new delhi,delhi,india
A:
It won't work, you won't get any output.  All you get is a heating up of the transformer due to the resistance of the primary winding.  The  reason is that a transformer works on the principle that a changing magnetic flux will induce a voltage in a loop of wire encircling that flux.  This is known as Faraday's Law of Induction.  You can read about it in any elementary E and M text.   So, no change in flux --> no induced voltage.

LeeH

(published on 08/18/2011)

## Follow-Up #1: AC and DC voltages as inputs to a transformer

Q:
can a transformer work on a variable dc supply? say output of a full wave rectifier. also, what will happen if a triangular AC waveform is used as an excitation in a transformer?
- Suyash (age 20)
Bhilai
A:
The short answer is that only the AC component of a mixed AC-DC input will be passed.
Wikipedia also has a nice description of how a transformer works:
http://en.wikipedia.org/wiki/Transformer

LeeH

(published on 12/20/2011)

## Follow-Up #2: Why does a transformer use alternating current only?

Q:
Why does a transformer can only use alternating current?
- Thivya (age 15)
Singapore
A:

We can divide a transformer into two subcomponents: 1) Primary windings, that create a magnetic field 2)Secondary windings on which a current is induced by changing magnetic fields. For the generation of a magnetic field, both AC and DC would work. Since the primary has some resistance, the current through it generates some heat and uses some energy from the current source.  But DC would generate a constant magnetic field, therefore you cannot harvest any energy in the secondary.

Tunc

(published on 09/06/2015)