Magnetics Business & Technology - July/August 2019 - 16

RESEARCH & DEVELOPMENT

The Economics of a Transformer
By Dr. Kevin G. McGivern, McGivern Technologies

How is the "Cost" of a Transformer Determined?
To many customers the cost of a transformer is simply the
monetary value at the time of purchase. In a broad sense this is
adequate. After all, the material cost of a device is one of the biggest, if not the biggest, driver of the selling price. When you add
the price differential between a transformer and other components on the circuit board you obtain a skewed view.
Understanding the Different Types of Transformers
I had a co-worker that stated to me rather bluntly: "I don't see
how there can be different types of transformers. I mean, they
are all just a bunch of wires wrapped around a core." This individual is a highly intelligent person. I have had other individuals
tell me that I practice "Black Magic" every time I design a transformer. How often have you heard these types of comments? If it
was once, it was too often.
Transformer design follows very specific equations that will
dictate how the device is going to work at any given frequency,
voltage, wave form, and current. While developing an intuition on
what the end design needs to look like is helpful, it is a learned
trait - not magic.
With that said. The requirements for a power supply transformer
and a current transformer are completely different. A pulse
transformer and a gate drive transformer are similar, but have
different requirements depending on load conditions, operating
frequency, and wave form.
The type of transformer effects all the material utilized in the
build. From the core to the insulation required, the core material
and shape, and the spacing between windings are dictated by
the requirements of the transformer.
How Cost is Defined
There are many ways to look at the "Cost" of a transformer. This
ranges from the cost of the material to the impact on the system.

Magnetics Business & Technology * July/August 2019

The most basic cost of the transformer is the time and material
to manufacture the device. A more complete picture is achieved
when the impact on the system is considered.
Efficiency
The overall efficiency of any system is based on the efficiency
of each individual component. The efficiency of the system will
never be more than any transformer in the system. There is more
to the efficiency of a transformer than the raw efficiency of a
transformer.
Stability
Stability is a key criterion to any system. A poorly designed
transformer has a dramatic effect on the stability. The capacitance and leakage inductance combine to define the shape of a
waveform. When these are combined with the inductances and
DCR's of each winding over-shoot and under-shoot are defined.
They also define the damping factor of the transformer. A poorly
designed transformer typically increases the number and size of
components used in conjunction with the transformer to increase.
Each of these added components are now a loss in efficiency.
Reliability
The reliability of a transformer is paramount to the reliability of
the system. Reliability is more than how long the transformer
will last. There are failure modes to a transformer that have a
dramatic cause- effect relationship in the system.
Hard Failure
This is identified by a short between the primary side of the transformer and the secondary side of the transformer. The root of this
problem lies in two primary failure mechanisms:
1.
Complete Break-Over - this is when a high voltage transient or sustained voltage between the primary and secondary
shorts through the insulation material.
2.

One of the windings is broken due to a high voltage.

www.MagneticsMag.com

http://www.MagneticsMag.com

Magnetics Business & Technology - July/August 2019

Table of Contents for the Digital Edition of Magnetics Business & Technology - July/August 2019