EE464-Static Power Conversion-II

class: center, middle

# EE-464 STATIC POWER CONVERSION-II

# Isolated Switching Power Supplies

## Ozan Keysan

## [keysan.me](http://keysan.me)

### Office: C-113 <span class="meta">•</span> Tel: 210 7586

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# Regulated Power Supplies
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- ## Regulated Output Voltage
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- ## Electric Isolation
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- ## Minimum size, weight
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- ## Minimum cost
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- ## Maximum efficiency

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# Linear Regulators

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# Linear Power Supplies
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# Linear Power Supplies
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- ## Low frequency transformer: large and heavy
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- ## BJT operates in linear region: dissipates heat
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- ## Efficiency is around 30-60%
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- ## Advantage:
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Minimum EMI Problems

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# Switching DC Power Supply
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<img src="./images/ee464/smps.png" alt="Drawing" style="width: 800px;">
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# Switching DC Power Supply
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## Multiple Output Case

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# Case Study:
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## [Apple Charger Teardown](http://www.righto.com/2015/11/macbook-charger-teardown-surprising.html)

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## [Apple Charger Teardown](http://www.righto.com/2015/11/macbook-charger-teardown-surprising.html)

<img src="http://static.righto.com/images/magsafe/components1-w750.png" alt="Drawing" style="width:600px;">
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## New Versions of Chargers

- ## [Apple 20W USB-C Charger Teardown](https://www.youtube.com/watch?v=W-FlBXTAKDs)

- ## [Teardown Apple 140W USB-C GaN Charger](https://www.chargerlab.com/teardown-of-brand-new-apple-140w-usb-c-gan-charger/)

- ## [USB Type-C PD: Power Delivery](https://www.st.com/content/ccc/resource/sales_and_marketing/presentation/product_presentation/group0/5a/b1/8e/6c/2b/0d/46/3c/Apec/files/APEC_2016_USB_Power.pdf/_jcr_content/translations/en.APEC_2016_USB_Power.pdf)

- ## [A Primer on USB Type-C and USB Power Delivery](https://www.ti.com/lit/wp/slyy109a/slyy109a.pdf)
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# Flyback Converter

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# Flyback Converter Evolution

## Start from the buck-boost converter

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# Flyback Converter Evolution

## Wound the inductor with two parallel wires

### Don't get confused with the dots yet!

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# Flyback Converter Evolution

## Isolate inductor wires (isolated converter)

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# Flyback Converter Evolution

## Modify turns ratio to adjust output voltage and direction to get positive output

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# Back to EE361
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## Ideal Transformer
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# Back to EE361

## Ideal Transformer

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# Back to EE361
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## Realistic Transformer Equivalent Circuit
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# Flyback Converter

## Let's ignore resistive parts and leakage flux for now

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# Flyback Converter with Transformer

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# Flyback Converter with Transformer

## Can you plot the operating modes?
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# Flyback Converter

## Switch ON

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# Flyback Converter

## Switch OFF

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# [Flyback Converter](https://www.plexim.com/academy/power-electronics/flyback-conv)

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# [Flyback Converter](https://www.plexim.com/academy/power-electronics/flyback-conv)

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# Flyback Converter

### Conversion ratio can be calculated in three different ways:

- ### Magnetic Circuit: Transformer Flux

- ### Steady state current

- ### Graphically: Voltage-seconds area of the inductor
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# \\(\dfrac{V_o}{V_d} = \dfrac{D}{(1-D)} \dfrac{N_2}{N_1} \\)
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## Switch Selection
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### Peak Switch Current
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### \\(\hat{I}_{sw}=  \dfrac{1}{(1-D)} \dfrac{N_2}{N_1} I\_o + \dfrac{N\_1}{N\_2} \dfrac{(1-D)T\_s}{2L\_m}V\_o\\)
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### Peak Switch Voltage
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### \\( \hat{V}_{sw} = V\_d + \dfrac{N_1}{N_2}V\_o\\)
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\\(=\dfrac{V\_d}{(1-D)}\\)

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# Flyback Converter: DCM

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# Flyback Converter: DCM

#### Voltage and currents in CCM, (VD: Diode voltage, VDS:transistor drain-source voltage)

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# Flyback Converter: DCM

#### Voltage and currents in CCM, (VD: Diode voltage, VDS:transistor drain-source voltage)

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### Flyback DCM vs CCM

### Efficiency is usually higher:
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- ### Soft turn-on for transistor (reduced switching loss)
- ### no reverse recovery loss in the diode

### Smaller core (better flux density utilization)

### Current peaks get higher
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- ### Higher current rating for diode and transistor
- ### Can cause increase in conduction losses

### DCM has a better stability in transient control

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# Flyback Example

### Hart 7.1

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# Reading Materials

- ## [The Flyback Converter](https://pdf4pro.com/view/the-flyback-converter-university-of-colorado-boulder-5bb172.html)

- ## [Flyback transformer tutorial: function and design](https://www.eetimes.com/document.asp?doc_id=1273089)

- ## [Flyback Converter Video](https://training.ti.com/understanding-basics-flyback-converter)

- ## [Designing a DCM flyback converter](https://www.edn.com/power-tips-98-designing-a-dcm-flyback-converter/)

- ## [Flyback DCM vs CCM](https://www.icbanq.com/icbank_data/online_seminar_image/Flyback_CCMVsDCM_Rev1p2.pdf)

- ## [The Difference between CCM and DCM Explained](https://www.monolithicpower.com/en/the-difference-between-ccm-and-dcm-explained)
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# Flyback Variations: Two Transistor Flyback
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- #### [Improving the Performance of Traditional Flyback with Two Switch Approach](https://www.ti.com/lit/an/snva716/snva716.pdf)

- #### [Operation & Benefits of Two-Switch Forward/Flyback Power Converter Topologies](https://www.embedded.com/operation-benefits-of-two-switch-forward-flyback-power-converter-topologies/)
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# Flyback Variations: Paralled Flyback
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<img src="./images/ee464/parallel_flyback.png" alt="Drawing" style="width: 500px;">
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# Forward Converter
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## Derived from the Buck Converter

<img src="./images/ee464/forward_converter.png" alt="Drawing" style="width: 700px;">
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# Forward Converter
## Let's obtain the output voltage characteristics

<!--
## Can you obtain the output voltage characteristics?

# Quiz -Q1
# Quiz -Q2

## Choose a duty cycle and turns ratio, to get 12V DC from a 200V DC input.

-->

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# Forward Converter

## A buck converter with added turns ratio

# \\(\dfrac{V_o}{V_d} =\dfrac{N_2}{N_1} D \\)

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# Forward Converter

## What happens at the instant when the switch is turned-off, if the transformer is not ideal?

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# Forward Converter

## A discharging path for Lm should be added.

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# Simple Solution: RCD Reset Circuit

## Magnetizing current dissipates through RCD circuit

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# Simple Solution: RCD Reset Circuit

## Cheap but inefficient

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# RCD Snubber

### Note a similar circuit can be used for the Flyback converter (to reduce inductance leakage ringing)
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### Suggested Reading: [Flyback Converter Snubber Design](http://ridleyengineering.com/images/phocadownload/12%20flyback%20snubber%20design.pdf)

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# Practical Forward Converter

## A transformer with two-primary windings
### Third winding is added to discharge the energy stored in Lm
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# Practical Forward Converter

## A transformer with two-primary windings
### Third winding is added to discharge the energy store

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# Forward Converter

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## Forward Converter: Switch is ON

### Lm is charged by input voltage, Lx is also charging
### D1 On, D2 Off, D3 Off

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## Forward Converter: Switch is OFF

### Lx feeds the load, Lm is discharged to the source: \\(i\_{1} = - i\_{Lm} \\)

### KCL: \\(N_1 i_1 = N_2 i_2 - N_3 i_3\\)

### For proper operation the transformer should be "reset" before next ON period
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## Forward Converter: Switch is OFF

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## Forward Converter

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## Forward Converter

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# Practical Forward Converter
### For proper operation the transformer should be "reset" before next ON period

## \\(t\_m < (1-D) T\_s\\)
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## \\(D\_{max}\\)
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\\(=\dfrac{1}{1+ (N\_3 / N\_1)}\\)

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### What happens if D is large, and transformer does not reset completely?
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#### In the figure Dmax=0.5

### Saturation, increased core losses, reduced Lm, problem in power transfer

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# Advantages over Flyback

- ## Better utilization of transformer (direct power transfer, higher)

- ## A gapless core can be used (higher Lm, less ripple)

- ## Output inductor and diode ensure continuous output current

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# Drawbacks compared to Flyback

- ## Increased cost (extra diode and inductor)

- ## Gain changes a lot in DCM

- ## Higher voltage requirement for MOSFET

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# Forward Converter Alternatives
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## Two-switch forward converter

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# Forward Converter Alternatives

## Two-switch forward converter

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# Two-switch forward converter

# Advantages:

- ## Does not require a snubber circuit

- ## Less voltage stress on MOSFETs

- ## Can supply multiple isolated outputs

- ## Low power losses and noise
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# Two-switch forward converter

# Disadvantages:

- ## Slightly more expensive

- ## Higher component count
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##  Interleaved forward converter

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# Forward Converter Reading Materials

- ## [Infineon, Forward Converter Design Note](https://www.mouser.com/pdfdocs/2-10.pdf)

- ## [Fairchild Forward Converter Application Note](https://www.onsemi.com/pub/Collateral/AN-4134.PDF)

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# Example:

## Hart - Power Electronics Ex. 7-4

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# Example:

## Hart - Power Electronics Ex. 7-4

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# Push-Pull Converter
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### Uses a center-tapped transformer

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# Push-Pull Converter

### Three operating sections

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# Push-Pull Converter

## Switch(T1) ON, Switch(T2) OFF

### D1 conducts, D2 reverse-biased
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### \\(v\_{x}= \dfrac{N\_2}{N\_1} V\_s \\)
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### \\(v\_{L}= v\_{x} - V\_o = \dfrac{N\_2}{N\_1} V\_s - V\_o  \\)

### \\(i\_L\\) increases linearly
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# Push-Pull Converter

## Switch(T2) ON, Switch(T1) OFF
### Symmetrical operation with the previous

### \\(v\_{x}= \dfrac{N\_2}{N\_1} V\_s \\)
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### \\(v\_{L}= v\_{x} - V\_o = \dfrac{N\_2}{N\_1} V\_s - V\_o  \\)

### \\(i\_L\\) increases linearly

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# Push-Pull Converter

## Both Switches are OFF
### for a period of \\(\Delta\\)
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### Both D1 and D2 conducts

### \\(I\_{D1} = I\_{D2} = 0.5 I\_{L} \\)

### \\(v\_{x}= 0 \\)
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### Therefore \\(v\_{L}= -V\_o  \\)

### Inductor discharges and feeds the load
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### Repeating waveforms for every Ts/2

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# Push-Pull Converter

## Repeating waveforms for every Ts/2

## \\(D T\_s + \Delta = \dfrac{T\_s}{2}  \\)

## \\(\Delta  = \dfrac{(1-2D)}{2}T\_s  \\)

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# Push-Pull Converter

## Output voltage characteristics?
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## Use the inductor voltage
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# \\(\dfrac{V_o}{V_d} =\dfrac{2N_2}{N_1} D \\)

### Twice of the forward converter
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# Push-Pull Converter
### Comparison of Magnetic Flux in the Core

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# Extra Materials

## Flyback Converter

#### [ECEN4517 Lecture Notes](http://ecee.colorado.edu/ecen4517/materials/flyback.pdf)

#### [Flyback Transformer Tutorial](https://www.eetimes.com/document.asp?doc_id=1273089)

#### [Optimised Flyback Design](http://www.eenewspower.com/content/step-step-optimised-flyback-design)

#### [Switch Mode Power Supply (SMPS) Topologies](http://ww1.microchip.com/downloads/en/AppNotes/01207B.pdf)

#### [ECE5797 SMPSs](http://ecee.colorado.edu/~ecen5797/course_material/Ch6slides.pdf)

#### [Flyback Converter, Transformer Design](https://coefs.uncc.edu/mnoras/files/2013/03/Transformer-and-Inductor-Design-Handbook_Chapter_13.pdf)

#### [Design Guide Flyback Converter](https://www.fairchildsemi.com/application-notes/AN/AN-4137.pdf)

#### [Design Guidelines for Flyback Converter](https://www.monolithicpower.com/Portals/0/Documents/Products/Documents/appnotes/AN069_r1.0.pdf)

### [Transformer Design Cookbook](https://www.digikey.com/Web%20Export/Supplier%20Content/Wurth_732/PDF/Wurth_CookbookforTransformerDesign.pdf?redirected=1)

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# Extra Materials

## Forward Converter

### [Forward Converter, Transformer, Inductor Design](https://coefs.uncc.edu/mnoras/files/2013/03/Transformer-and-Inductor-Design-Handbook_Chapter_14.pdf)

### [Forward Converter Design](https://www.mouser.com/pdfdocs/2-10.pdf)

### [Forward Converter Tutorial Video](https://training.ti.com/topology-tutorial-what-forward-converter)
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# Design Exercise
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## [Forward Converter Design](https://www.mouser.com/pdfdocs/2-10.pdf)

### [ETD 34/17/11](https://www.tdk-electronics.tdk.com/inf/80/db/fer/etd_34_17_11.pdf)

### [Skin Effect Calculator](https://www.allaboutcircuits.com/tools/skin-depth-calculator/)

### [AWG Conductors](https://en.wikipedia.org/wiki/American_wire_gauge)
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## You can download this presentation from: [keysan.me/ee464](http://keysan.me/ee464)