DCM rev. IL Vx Ton Toff T Ts Vx Vin VL Vin-Vo Vo -Vo - - PDF document

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DCM rev. IL Vx Ton Toff T Ts Vx Vin VL Vin-Vo Vo -Vo - - PDF document

May 29, 2023 619 likes •788 views

Mor M. Peretz, Switch-Mode Power Supplies [2-1] DCM rev. IL Vx Ton Toff T Ts Vx Vin VL Vin-Vo Vo -Vo [2-2] Mor M. Peretz, Switch-Mode Power Supplies Synchronous rectifier No DCM ! IL Ton Toff 1 Mor M. Peretz,

slide-1
SLIDE 1

1

Mor M. Peretz, Switch-Mode Power Supplies

[2-1]

DCM – rev.

Ts Ton Toff T’ IL VL Vx Vx Vin-Vo

  • Vo

Vin Vo

Mor M. Peretz, Switch-Mode Power Supplies

[2-2]

Synchronous rectifier

No DCM !

Ton Toff IL

slide-2
SLIDE 2

2

Mor M. Peretz, Switch-Mode Power Supplies

[2-3]

Capacitors

  • Capacitor types
  • Output voltage ripple
  • Real capacitor
  • Parallel connection
  • Load step

Mor M. Peretz, Switch-Mode Power Supplies

[2-4]

Capacitor types

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

slide-3
SLIDE 3

3

Mor M. Peretz, Switch-Mode Power Supplies

[2-5]

Output voltage ripple

Buck

2 1 2 Ts 2 IL Q C Q Vc

  • IC

Vc VESR fs 8C IL Vc

ESR ESR

R IL V

  • Mor M. Peretz, Switch-Mode Power Supplies

[2-6]

Output voltage ripple

Boost

  • 2

IoTon Q time

  • n

Ton C Io Vc IC Vc VESR DTs 2RC Vo Vc

ESR ESR

R ID V

slide-4
SLIDE 4

4

Mor M. Peretz, Switch-Mode Power Supplies

[2-7]

Real capacitor

fC 2 1 C 1 Z

  • idea

l

f 20lg(|Z|)

  • 20db/dec

Mor M. Peretz, Switch-Mode Power Supplies

[2-8]

Parallel connection

100µ 0.1µ +

f1 fm f 20lg(|Z|)

C1 C2

f2

dB C f 2 1

1 1

  • dB

C f 2 1

2 1

  • dB

C f 2 1

2 2

  • dB

C f 2 1

1 2

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SLIDE 5

5

Mor M. Peretz, Switch-Mode Power Supplies

[2-9]

Load step

Ideal response

tS Vo t

tS Vo t ) ESR ( V

  • Practical response

C1 C2 R1 R2 S

Mor M. Peretz, Switch-Mode Power Supplies

[2-10]

Losses of SMPS

  • Conduction losses
  • RMS current
  • Resistor
  • MOSFET
  • ESR
  • Average current
  • Diode
  • IGBT
  • Switching losses
  • CV2
  • Heat conduction
slide-6
SLIDE 6

6

Mor M. Peretz, Switch-Mode Power Supplies

[2-11]

Conduction losses

V I P

  • T

dt I V T 1 P

Mor M. Peretz, Switch-Mode Power Supplies

[2-12]

Conduction losses Resistor

I V Power losses are function of RMS current Why???

  • T

dt I V T 1 P

Fourier series:

slide-7
SLIDE 7

7

Mor M. Peretz, Switch-Mode Power Supplies

[2-13]

Conduction losses

RMS calculation of typical waveform

D Ipk Irms 3 Ipk Irms

2 2

3 2 I Iav Irms

  • 2

2

3 2 I Iav D Irms

  • Mor M. Peretz, Switch-Mode Power Supplies

[2-14]

Conduction losses MOSFET

I DS_ON 2 2 RDS_ON

R 3 2 I Iav D P

slide-8
SLIDE 8

8

Mor M. Peretz, Switch-Mode Power Supplies

[2-15]

Conduction losses ESR

I

ESR 3 2 I Iav P

2 2 ESR

  • How to calculate ESR losses?

Topology dependent

Mor M. Peretz, Switch-Mode Power Supplies

[2-16]

Conduction losses Diode

I Conducting diode is a voltage source Power dissipation is related to the average current

D D

V Iav P

slide-9
SLIDE 9

9

Mor M. Peretz, Switch-Mode Power Supplies

[2-17]

Conduction losses

Example

  • Buck converter
  • Vin = 10v ; Vout = 5V ; Iout = 5A ; fs=100kHz
  • L = 100uF
  • RDSon=10mOhm ; VD=1V ; ESR=50mOhm
  • Calculate efficiency

Mor M. Peretz, Switch-Mode Power Supplies

[2-18]

Buck converter

Example - solution

slide-10
SLIDE 10

10

Mor M. Peretz, Switch-Mode Power Supplies

[2-19]

Switching losses

fs 2 V C P 2 V C E

2 max DS sw 2 max DS sw

  • dss

C

Mor M. Peretz, Switch-Mode Power Supplies

[2-20]

Switching losses

Isw VDS fs tr 3 IswV fs 2 E E P tr 6 IswV dt t tr V V t tr Isw E E

DS

  • ff
  • n

SW DS tr DS DS

  • ff
  • n
slide-11
SLIDE 11

11

Mor M. Peretz, Switch-Mode Power Supplies

[2-21]

Thermal considerations

  • Power coded to source
  • Temperature coded to voltage
  • Thermal coefficient - resistance

Mor M. Peretz, Switch-Mode Power Supplies

[2-22]

Thermal considerations

Example

  • Power to dissipate: 20W
  • j-c = 1 oC/W ; c-HS = 1 oC/W
  • Tjnct = 100 oC ; Tabm = 40 oC
  • Calculate HS-amb (determine the heatsink)
slide-12
SLIDE 12

12

Mor M. Peretz, Switch-Mode Power Supplies

[2-23]

Improving efficiency

Example – MC34063 (onsemi) step up/down converter

Mor M. Peretz, Switch-Mode Power Supplies

[2-24]

Improving efficiency

Example – MC34063 (onsemi)

Step-up (Boost) configuration

slide-13
SLIDE 13

13

Mor M. Peretz, Switch-Mode Power Supplies

[2-25]

Improving efficiency

Example – MC34063 (onsemi)

External BJT switch

Mor M. Peretz, Switch-Mode Power Supplies

[2-26]

slide-14
SLIDE 14

14

Mor M. Peretz, Switch-Mode Power Supplies

[2-27]

Mor M. Peretz, Switch-Mode Power Supplies

[2-28]

slide-15
SLIDE 15

15

Mor M. Peretz, Switch-Mode Power Supplies

[2-29]

Mor M. Peretz, Switch-Mode Power Supplies

[2-30]

slide-16
SLIDE 16

16

Mor M. Peretz, Switch-Mode Power Supplies

[2-31]