1. An Electronic Device, and also a Action Hero…
Transformers
An Electronic Device, and also a Action Hero…

2. Transformers Transfers electrical energy from one circuit to another.
No physically electrical connection between the circuits.
May involve changes in voltage and current.
Frequency does not change.

3. Construction Primary coil or winding. Secondary coil or winding.
Neither are connected to each other.

4. Construction
Why doesn’t current jump from one winding to the next in a transformer or inductor?
The wires inside a transformer and inductor are covered in a varnish or enamel that insulates one winding from the next.

5. How Transformers Function
The primary winding receives the source AC and creates a changing magnetic flux.
The secondary winding receives it’s energy from the magnetic flux created by the primary winding and sends it to the load.
The core material provides a path for the magnetic lines of flux.

6. Explaining how the magnetic field “cuts” the windings in a transformer
Explaining how the magnetic field “cuts” the windings in a transformer. (again)

7. Coupling Circuits (continued)
The DC component is not transferred.

8. 3 Types of Transformers Step-Up Transformer Step-Down Transformer
It delivers higher voltage than the source, aka, it steps the voltage up. The voltage on the secondary side is higher than the primary side.
Step-Down Transformer
It delivers lower voltage than the source, aka, it steps the voltage down. The voltage on the secondary side is lower than the primary side.
One-to-One Isolation Transformer
The voltage on the primary is the same as the secondary. There is no increase or decrease in voltage.

9. What would the output of a one-one transformer be if the input is a square wave?

10. Transformer Example

11. The Core of a Transformer
The material of the core can be made from a variety of materials. It can also be made out of air.
Typically an air core is useful for high frequency applications while iron cores are used for low frequency applications.

12. If the core is made out of iron, it is usually in the form of a shell core.
Laminations are insulated from each other.
This makes shells electrically insulated from each other (good for less eddy currents) but not magnetically isolated from each other.
Similar to a row of staples
in a stapler.

13. Take 5 minutes and read section 19.2.2 to yourselves.
What happens to the fuse on the primary side of a transformer if there is a short in the secondary?
The fuse blows even though they aren’t connected!!!!!!!!!

14. RVOTD: Danger, Will Robinson!
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15. High Voltage Lineman at work
KZ0
Not sure if already shown

16. Transformer Simulation

17. Transformer Ratios
You can calculate if a transformer is a step-up, step-down, or one-to-one by simply looking at how many turns there are of wire on the primary and secondary sides.
It can also be given by the equation below Ns Vs Vp Np
Where:
Np = number of turns in the primary
Ns = number of turns in the secondary
Vp = voltage applied to the primary
Vs = voltage induced in the secondary
Now that you understand how a transformer functions, we can quantify the variables.
The total voltage induced into the secondary winding (Vs) is mainly determined by the ratio of the number of turns in the primary (Np) to the number of turns in the secondary (Ns) and by the voltage applied to the primary (Vp).

18. Useful Ratio Form Ns Vs Vp Np
Sometimes you may be given a “turns” ratio. This may be one number that represents:
Note that you will need three of the four numbers to compute the remaining variable except in the case that you are given a ratio for the turns instead of the turns for each winding. In such a case, you will only need 2 of the 3 numbers to compute the remaining variable. Np Ns
such as 10.0, or a ratio like 10:1

19. Example #1:
Vs?
120V 50
200 Ns Vs Np Vp 50 Vs
120
200 Vs
30V

20. The Turns Ratio Common ways to express the ratioNp Ns
Common ways to express the ratio
10:1
or 1:10
Which of these steps-up voltage?
Ratio is always quoted “Primary to Secondary”
Ratio does not indicate the number of turns

21. Example #2: Step-down Transformer Aka “Buck” Transformer Find: Vp Vs
7:1
If there is less voltage across the secondary than across the primary, the secondary must have fewer turns than the primary. This type of transformer is called a step-down transformer because the voltage is less coming out of the unit. Vp Vs Vp Np Ns Vp 5V 7 1 Vp
35V

22. Example #3: “Boost” Transformer Find: Vs Vs Vp Np Ns Vp Vs Ns Np Vs
Transformer labeled:
1:5
Vs? Vs Vs Vp Np Ns Vp Vs Ns Np Vs
600V

23. What do we lose in the process?
Voltage does not just magically increase out of thin air. Something must be lost in the process, or else we would be making energy from nothing.
What do we lose in the process?
Current!

24. RVOTD http://www.youtube.com/watch?v=uXEPy6Za6 cI
High Current, low voltage (1V)
50kAmp powersupply, shorting crow bars

25. If we have a perfectly efficient transformer, the power transferred from one side to the other must be kept the same.
Since P = VI, the Voltage multiplied by the current on the primary must be equal to the voltage multiplied by the current on the secondary.
Pp = VpIp = VSIS = PS

26. Pp = VpIp = VSIS = PS IpNp = ISNS
Therefore, if the voltage increases then the current must decrease to keep the power the same.
So current can also be calculated using the number of turns on the primary and secondary side.
IpNp = ISNS

27. Example
IpNp = ISNS
A transformer has 100 turns in the primary and 600 in the secondary. There is 3A of current in the primary. What is the value of current in the secondary?

28. Example
IpNp = ISNS
A transformer with a turns ratio of 8:1 has 2A of current in the primary. What is the value of secondary current?
IS = 16A

29. Example – try these on your own

30. RVOTD

31. Ignition Coils are Transformers
From 6:17 minutes til end of ignition coil segment
95&psid=0&sid=0&State=&title=Ignition%20System%2 0Operation&IsSearch=N&parentSeriesID=16198&tScrip t=0#
Type into search box in films on demand

32. Transformer Schematic Symbol
Sometimes there are taps off the secondary.
Sometimes there are multiple secondary windings.

33. Multiple Winding Transformers used in power supplies

34. Variac or Auto-Transformers

35. Phase Dots In Phase Out of phase
Phase Dots refer to whether the voltage on the primary side is in phase with voltage on the secondary side. There are either in phase or 180˚ out of phase.
In Phase Out of phase

36. Phase Dots
In Phase Out of phase

37. Maximum Power Rating for a Transformer
Transformers have a maximum power rating.
This means the wires can only handle so much combined voltage and current before they break down.
Transformers usually have their power rating printed right on them.
A typical transformer could be labeled 24VAC, 3A, 60Hz. This implies a 24Vrms secondary, a 3A maximum secondary current and 60Hz frequency application. (It is understood the primary voltage is 120V.)

38. Measuring for transformer type.
You can measure the actual physical resistance on the primary winding and the secondary winding.
This will tell you if you have a step-up, step- down, or one to one transformer.
Do you think the windings in the secondary side of a transformer has more or less resistance than the primary for a step down transformer?
Why – because there are more windings for higher voltage and those windings are usually thinner because they don’t have to handle as much current, this causes the resistance to go up even more.

39. Review –
What type of transformer has a larger voltage on the secondary than the primary?
Step up transformer
In a step down transformer, what has more resistance, the primary or the secondary?
Primary
Suppose you overpowered your transformer, what do you think will happen?
Melt wires, cause short between primary and secondary, maybe fire.

40. If the voltage is increased in the secondary side, what is decreased?
Current
What are the phase dots used for?
To determine if primary and secondary voltages are in phase or out of phase
What causes an induced voltage on the secondary?
A changing magnetic field cutting across the turns of the secondary windings which was caused by a changing current in the primary windings.

41. Do impedance matching transformers on white board.

42. Misc Oscope Questions
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