[PDF] - Power elements 5.1 Conduction loss calculations 5.2 Diode 5.2.1 PDF Document

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 1]

Power elements

5.1 Conduction loss calculations 5.2 Diode 5.2.1 Types of diodes 5.2.2 Diode conduction losses 5.2.3 Diode recovery 5.3 Power switches 5.3.1 BJT 5.3.2 MOSFETs 5.3.3 IGBT 5.3.4 Other switches 5.4.4 Switching losses 5.4 Capacitor 5.4.1 Capacitor types 5.4.2 Specifications, model, ESR 5.4.3 Assignments (∆VESR) 5.4.4 Capacitor losses

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 2]

Conduction Losses

) domain time ( dt I V T 1 P

T

∫ ⋅ =

Z I V I t V t t V I× T P

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 3]

Resistor

Periodic waveform

R I P I } dt ) I ( T 1 { } dt ) I ( T 1 { R P dt I V T 1 P R I V

2 ) rms ( R R rms T 2 R s T 2 R s R T R R s R R R

s s s

= ≡ ∫ ∫ = ∫ ⋅ = ⋅ = IR VR

t

R

I ton toff TS t

R

V TS

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 4]

) t cos( V V V ) t cos( I I I

i i i av i i i av

∑ ω + = ∑ ω + = ) domain time ( dt I V T 1 P

T

∫ ⋅ = Conclusion:

Only V,I components of same frequency produce

real power.

DC → ω=0

m n if dt ) t ( Cos ) t ( Cos

T m n

≠ = ∫ ω ω

Average power

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 5]

} dt ) I ( T 1 { I

s

T 2 R s rms

∫ = ∑ =

i 2 i rms

) I ( I ∑ =

i 2 i rms

) V ( V I1, I2, I3 …

f different frequencies

V1, V2,….

Average power

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 6]

Consider only ton Pon= (Im)2 R Pav= Pon ton/Ts= PonDon

n

m rms 2 rms

n

2 m av

D I I I R D R I P = ⋅ = ⋅ ⋅ =

IR VR t TS IR Im t IR Im t

Example 1

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 7]

Example 2

R 3 I P

2 pk R =

t T I I

pk ⋅

= This is an AC signal Iav = 0 !

3 I 3 I 3 t T I dt t T I T 1 I

pk 2 pk T 3 3 2 pk T 2 pk rms

= = =       =

∫

t Ipk

Ipk

TS

2 TS 2 T

S

t T

T Ipk

Ipk I

3 I I

pk rms =

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 8]

Example 2 (Cont.)

t Ipk

Ipk

TS

2 TS 2 TS

3 I I

pk rms =

For each of the sub- triangle:

Therefore for complete waveform:

3 I I

pk rms =

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 9]

Example 3

Separate into waveforms

f different frequencies

assuming a repeating wave: t toff TS Ipk I ∆ ton I t ton ton I

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 10]

t t

av

I

ton DC I ∆

Not like this !

Why ?

t ton ton I Ipk I ∆ Iav

t t

av

I

ton DC 2 I ∆ 2 I ∆

Waveform decomposition

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 11]

3 1 2 I ) rms ( I ) av ( I ) 2 I I ( I

2 I rms pk av

∆ = = ∆ − =

∆ 2 2 av

n

rms 2

) 3 1 2 I ( I ) t ( I ∆ + = t t

av

I

ton DC 2 I ∆ 2 I ∆ 2 I ∆

pk

I

Waveform decomposition

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 12]

n

2 2 av rms 2

D ) 3 1 2 I ( I I ⋅       ∆ + =

2 2 av

n

rms

) 3 1 2 I ( I D I ∆ + =

2 2 pk

n

rms

) 3 1 2 I ( ) 2 I I ( D I ∆ + ∆ − = R I P

2 rms R

⋅ =

s

T :

ver

power the Averaging t toff TS Ipk I ∆ ton I

2 2 av

n

rms 2

) 3 1 2 I ( I ) t ( I ∆ + = t ton ton I 12 I I D I

2 2 av

n

rms

∆ + =

Waveform decomposition

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 13]

1.Diode 1.1 Types of diodes 1.2 Diode conduction losses 1.3 Diode recovery

2. Power switches

2.1 BJT 2.2 MOSFETs 2.3 IGBT 2.3 Other switches

3. Capacitor

3.1 Capacitor types 3.2 Specifications, model, ESR 3.3 Assignments (∆VESR) 3.4 Losses

Switching Elements

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 14]

Diodes

Silicone - Slow →Fast Schottky - Fast

STATIC Si Schottky ID VD 0.7V 0.4V

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 15]

Diode conduction losses

ID VD

VD = VF ≈ constant

VF I

P ?

VF=DC frequency=0 Only DC components of I are important: P = Iav VF

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 16]

Reverse current at switch turn on

Diodes recovery

Vin L C R Vx Vo

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Prof. S. Ben-Yaakov , DC-DC Converters

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L - parasitic inductance Reverse Recovery of diode

t t ID IF L V trr VD ~VF VO

Diode recovery

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 18]

L1<L2<L3 Ipk, trr are function of IF, L, T

t ID IF Ipk L1 L2 L3

Diode recovery

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 19]

Diode conduction losses

IDav = Iav • Doff P = IDav• VF

t Doff Don ID t IL Iav t VD

S Vin D L C R IL ID

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 20]

Power Switches

BJT MOSFET IGBT G C E G D S C B E G C E G D S N P N C B E

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 21]

In linear region At saturation

}

IB IC IB(ON) VCE VCE sat

fe C B B fe C

h I I I h I = → =

fe C B

h I I >> C B E

BJT STATIC CHARACTERSTICS

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 22]

Relatively slow (storage time)

Replaced by MOSFET or IGBT Still is use in lamp ballasts and in very high

power applications (motor drive)

BJT Drive problems

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 23]

) ON ( DS D DS

R I V ⋅ = Ω − Ω → m 10 10 R

) ON ( DS

}

VGS VGS(ON) ID VDS VDS(ON) RDS(ON)

Power MOSFETS

Parallel connections of many basic MOSFET cells

MOSFET STATIC CHARACTERSTICS

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 24]

) ON ( DS

R

DS

V MOSFET 500V

RDSon as a Function of Breakdown Voltage

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 25]

Temp RDS(ON)

Permits parallel connection of MOSFETs

RDS(ON) as a Function of Temperature

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 26]

p channel

Gate voltage

Normal : 15V -15V Logic level: 5V -5V n channel

more popular less expensive

MOSFET

n channel

Internal diodes

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 27]

IGBT

Similar to BJT but faster Same gate voltage as

MOSFET VCE(sat)

Slow IGBT - 1V Fast IGBT - 3V

}

IC VCE VGE VCE(sat) IC

G C E

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 28]

Other Switches

SCR - low frequency no forced turn off MCT - SCR+FET input GTO - turn on and off; slow, high current

SLIDE 15

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 29]

MOSFET → Rds(on) BJT, IGBT →VCE (sat) Pd(MOSFET) →(Irms)2 Rds(on) Pd( BJT, IGBT) → Iav VCE (sat)

Conduction Losses of Active Switches

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 30]

Example:

L=10uH; fs= 100kHz; Rds(on)= 1 Ω Vin=25V; Vo=100V; Pout=100W

uS 5 . 7 f D t uS 5 . 2 f D t 75 . D 25 . D D 1 25 100 D 1 V V Amp 1 100 100 V P I P V I

s

n
n

s

ff
ff
n
ff
ff
ff

in

=

= = = = = = = = = = =

MOSFET Vin L C R Vx Vo

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 31]

t TS IL L Vin Iav I ∆ ton toff

Amp 3 u 5 . 7 u 25 10 t L V I

n

in

= = = ∆ Amp 1 V P I

av

= = t IS Iav=1A

A 3 I = ∆

Example:

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 32]

W 063 . 12 P A 47 . 3 I R I P A 47 . 3 75 . 3 5 . 4 D 3 1 2 I I I

d rms )

n

( ds 2 rms d 2 2

n

2 2 av rms

= = = =       + =       ∆ + = Iav=4A ∆I=1A RDS(on)=1ohm Don=0.75 t TS IL Iav I ∆ ton toff

Example:

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 33]

Over useful temp: Rds(on) =1.5 x Rds(on)[250C]

The limitation:

Junction Temp. Tj: 1200C- 1750C

RDS(ON) as a Function of Temperature

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 34]

IMPORTANT

Parallel connections of a number of MOSFETs is possible because of the positive temp coefficient of Rds(on)

Parallel connection

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 35]

2 CV2

dss

C heat to lost f 2 V C

s 2 max dss

→       Switching losses (overlap) also linear with fs! Linear with fs!

Losses

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 36]

control

GS

V

S

V

S

V

S

I

d

J

switching

P t t t

Switching losses due to overlap Pd linear with fS !

Switching losses

SLIDE 19

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 37] S

V

S

V

S

I t

r

t

r

t

S

T

r S S r S t r S

t 6 V I dt t t 1 1 V t t I E E

r

ff

d

n

d

=       −      

∫

⋅

≈ ≈

S r S S r S S S S

n

d S

ff

d

n

d S d d

f t 3 V I t T 3 V I T E 2 T E E T E P = ≈ ≈ + = =

Switching losses due to overlap Pd linear with fS !

Switching losses

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 38]

Heat conduction

Equivalent circuit P→ I T→ V → R

w c °

θ

FET Isolation Heatsink P

+

j

T

C

T

HS

T

ambient

T

ambient

T

HSAIR

θ

CHS

θ

jC

θ

SLIDE 20

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 39]

jC

θ Very small transistors Large Modern MOSFET T247 Isolator HS Surface-Airspeed θ HS-AIR w c 20° w c 5 . ° w c 1 5 . ~ ° ÷ w c 5 . 10 ° ÷

Transistors’ Data

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 40]

15(θjC+θCHS+θHSAIR)+25=110 ºC 15(1+1+x)=85 θHSAIR= - 2 = 15 85 W C 6 . 3 °

Example

Pd=15 , Tjmax=110 θjC =1 , Tamb(max)=50 θCHS=1 , Find θHS-AIR w c ° w c ° c ° c ° w

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 41]

Assignment

V2 TD = 0 TF = 0.01u PW = 10u PER = 20u V1 = 0 TR = 0.01u V2 = 15 Dbreak D1

ut_gnd

gate L2 {L1*(n*n)} RL {Load} drain V1 {Vin} R4 10meg

ut

C1 220u IC = 6 K K1 COUPLING = 1 K_Linear L1 = l1 L2 = l2 PARAM ET ERS: n = 0.5 Vin = 12 Load = 10 L1 = 300u

+

+
Sbreak

S1 L1 {L1}

Modify circuit to include RS=500mΩ. Find by simulation losses on switch and overall efficiency.

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 42]

Capacitors

Materials: Tantalum Aluminum Paper Plastic Teflon Polypropylene Minerals Mica Polarized (electrolytic) Non Polarized C < 10µF

SLIDE 22

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 43]

Capacitors

Constructions:

dielectric metal metal

Wrapped Sintered

metal dielectric metal metal

xide

electrolyte Comb structure

metal electrode porous body electrolyte

Sintered Electrolyte Capacitor

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 44]

Capacitors

fC 2 1 C 1 Z π = ω = idea l

f 20lg(|Z|)

20db/dec

Wrapped capacitors

will tend to have higher inductance

C L R Capacitance Series inductance Equivalent series resistance (ESR)

SLIDE 23

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 45]

Practical C

f1 f2 f 20lg(|Z|) ESR C1 C2 db(Z2) db(Z1)

1 2

C C >

1 1 2 1

C f 2 1 C f 2 1 π < π

1 2 2 2

C f 2 1 C f 2 1 π > π

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 46]

Philips ceramic capacitors

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 47]

100µ 0.1µ +

Why?

At f1: At f2:

f1 fm f 20lg(|Z|)

C1 C2

f2

dB C f 2 1

1 1

      π dB C f 2 1

2 1

      π dB C f 2 1

1 2

      π dB C f 2 1

2 2

      π dB C f 2 1 Z

2 1 1

      π ≈ dB C f 2 1 Z

2 2 2

      π ≈

Electrolytic Ceramic (comb)

Parallel connection of Capacitors

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 48]

Specifications of capacitor

Capacitance Maximum voltage Maximum current Inductance or plot ESR, Sometime:

) frequency test ( CR tg

ESR

= ω ω = δ

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Prof. S. Ben-Yaakov , DC-DC Converters

[5- 49]

Implication- Load Step

Ideal response

tS Vo t

tS Vo t ) ESR ( V ∆ Practical response

C1 C2 R1 R2 S

Prof. S. Ben-Yaakov , DC-DC Converters

[5- 50]

Capacitor losses

S Vin D L C R IL IC IR control IL t Iav t Iav IR IC t AC DC I ∆ I ∆

ESR I P

2 Crms ⋅