Output Transformer Design
Would you like to know how to design output transformer in
step by step?
1st, calculate the inductance required. For higher primary impedance, larger
inductance is needed and therefore larger core and / or more turns are needed.
This also affects the high frequency response.
L = Z / (2 * pi * f)
2nd, calculate the primary voltage and current.
If the power (Watt) and impedance are know, then you can use Ohm’s law to
calculate the voltage and current needed.
E = sqrt (Z x W)I = E / Z
3rd, calculate the secondary voltage and current.
Secondary voltage can be calculated from impedance ratio.
E2 = sqrt ((E12 x Z2) / Z1)E2 / E1 = I1 / I2I2 = (I1 x E1) / E2
4th, determine the core size and material. Since
the core size will be dependent of the materials used and manufacturer
electrical properties, we will not go into details. For small low level unit,
material can be 50% or 80% nickel. For others, perhaps 4% silicon steel is
needed. One can refer to the manufacturer datasheet that is usually specified
for 50-60Hz operation, and de-rate it for 20Hz audio usage. The manufacturer
datasheet should provide formula for inductance calculation. Follow that and
choose the right core size to meet the inductance requirement.
5th, determine primary / secondary wire size. This
can also be found from manufacturer datasheet of the wires used.
6th – calculate if the core size can fit the
wires needed, for both primary and secondary turns included. Primary wire
should take up 50% and vice versa.
7th – determine the high frequency response. High
frequency response is controlled by the impedance and the leakage inductance.
The leakage inductance is proportional to the square of the turns. Therefore,
the higher the number of turns, the lower the high frequencies limit. The
number of turns is already set to get the needed primary inductance for low
frequency response. So, it’s a balance between low and high due to the law of
physics.
Leakage inductance can be reduced by interleaved primary and
secondary windings. Interleave as in split the windings and wind primary first,
the followed by secondary, and so forth. Some examples of interleaving could be
1:2, 3:4, and etc.
The high frequency limit can be calculated with respect to
the leakage inductance and the normalized impedance, as follow:
Zn = (N1/N2)2 x Z2 + Z1F2 = Zn / (2 * pi * L-leakage)
Do note that slopping winding or improper winding
implementation will increase the leakage inductance. The windings must be
directly above each other. Commonality is called for in every case if the wires
cannot fill out the core, like equal spacing, spiraling and etc. No cross over
windings is allowed. Good and patient workmanship is required to obtain excellent
results.
That sums up the output transformer design introduction.
There are many more steps involved and we shall continue again in future
articles.
J&K Audio Design
29/12/2013
Product Lists
Level 0
Product Lists
Level 0
Level 3: depends on type, size and complexity. Email us for details.
* Finished
amplifiers, DACs, audio gadgets, upgrades and repairs - this is not our
core business and we do it out of passion. We do not
have fixed models, fixed price and we customize for each individuals.
The sky is limit of creativity.
* Our product lines are always improving and increasing. If you do not see what you want, contact us!
* Please email for volume discounts, distributor and OEM pricing.
No comments:
Post a Comment