1. EET 423 POWER ELECTRONICS -2
Prof R T Kennedy

2. POWER INDUCTORS
Prof R T Kennedy

3. THIN INDUCTOR LOW PROFILE CONVERTER
Prof R T Kennedy

4. INDUCTOR TYPES MOLDED INDUCTOR AIR CORED INDUCTOR ‘AIR’ CORED INDUCTOR
TOROIDAL INDUCTOR
The molded inductor is marker brown-black-black-gold, meaning 10 x 100 μH, or 10 μH, with 5% tolerance.
Other inductor types are often unmaked, with value indcated on packaging materials only.
Prof R T Kennedy

5. SELECTING INDUCTORS Converter Currents waveforms operation mode
• Parameter Selection
inductor specification
Inductor Losses
Construction Type
coil v chip Inductors
Electromagnetic Interference (EMI / EMC)
shielded v non shielded inductors
Prof R T Kennedy

6. BUCK-FORWARD CONVERTER CURRENT
INDUCTOR CURRENT
IL,M
IL,m
IL,av = Iout t
Prof R T Kennedy

7. INDUCTOR RIPPLE CURRENT
INDUCTOR CURRENT
IL,M
IL,m
IL,av = Iout t
SELECT L: BASED on pk-pk RIPPLE
Prof R T Kennedy

8. BUCK & FORWARD OPERATION MODE
SELDOM DCM
increased capacitor requirements
multiple outputs poor cross regulation
Prof R T Kennedy

9. HIGHER RIPPLE-DC RATIO SMALLER RIPPLE-DC RATIO
INDUCTANCE VALUE
Ein = 2.7 V V
Vout = 1.5 V
fsw = 3 MHz
Iout = 800 mA
L = 1 mH
HIGHER RIPPLE-DC RATIO
> LOSSES
SMALLER RIPPLE-DC RATIO
> SIZE
Prof R T Kennedy

10. constant inductor voltageIL t J
constant inductance
constant inductor voltage
Prof R T Kennedy

11. IL t L
excess resistance
less efficient
Prof R T Kennedy

12. inductor current exceeds IsatIL t L
peaky current
reduced L
inductor current exceeds Isat
Prof R T Kennedy

13. TYPICAL INDUCTOR SPECIFICATION
DESIGN LIMITING FACTORS
TEMPERATURE RISE
EFFICIENCY
due to
CORE & WINDING LOSSES
CORE SATURATION
Prof R T Kennedy

14. INDUCTOR LOSSES SKIN EFFECT PROXIMITY EFFECT WINDING (COPPER) CORE
HYSTERESIS DC
(DCR) AC
(ACR)
EDDY CURRENT
SKIN EFFECT
PROXIMITY EFFECT
Prof R T Kennedy

15. TYPICAL INDUCTOR SPECIFICATION
Prof R T Kennedy

16. DC WINDING (COPPER) LOSS
INDUCTOR DC RESISTANCE
DC WINDING (COPPER) LOSS
Prof R T Kennedy

17. DC RESISTANCE v TEMPERATURE
Prof R T Kennedy

18. INDUCTOR AC RESISTANCE
SKIN EFFECT
due to eddy currents produced by the ac current
add to the outer conductor current
subtract from the inner conductor current
frequency increase
majority of the current flows on the surface
Prof R T Kennedy

19. AC RESISTANCE: SKIN EFFECT
current
density
Prof R T Kennedy

20. AC RESISTANCE v FREQUENCY
Prof R T Kennedy

21. INDUCTOR AC RESISTANCE v FREQUENCY
Coilcraft LPO
AC RESISTANCE LOSSES
Prof R T Kennedy

22. AC v DC RESISTANCE
Prof R T Kennedy

23. COMPARATIVE LOSSES
Prof R T Kennedy

24. INDUCTOR SELF RESONANT FREQUENCY
at which
inductor winding inductance
resonates naturally
with
winding distributed capacitance
Prof R T Kennedy

25. INDUCTANCE v CURRENT
Prof R T Kennedy

26. INDUCTANCE v CURRENT
Prof R T Kennedy

27. SATURATION CURRENT v TEMPERATURE
25 oC
85 oC
Prof R T Kennedy

28. CORE SATURATION reduced inductance  increased  noise
Prof R T Kennedy

29. INDUCTOR RATED CURRENT
RATED CURRENT: smaller of saturation and RMS
Prof R T Kennedy

30. Isat >> DATASHEET SPEC !!!!
Prof R T Kennedy

31. INDUCTOR TEMPERATURE RISE
Prof R T Kennedy

32. FARADAY’S VOLT-TIME INTEGRAL
INDUCTOR VOLTAGE V1 t1
INDUCTOR CURRENT t2 V2 t
I m
I M T
current start and finish at same value
EQUAL AREAS
Prof R T Kennedy

33. ‘IDEAL’ BUCK ANALYSIS CCM VOLT-TIME INTEGRAL APPROACH
INDUCTOR VOLTAGE IL
Ein -Vout VL
area A
area B
-Vout
Dsw T
Dfwd T t
Prof R T Kennedy

34. INDUCTOR CURRENT WAVEFORMS
CCM or DCM operational mode
component current stress
capacitor ripple current
output voltage ripple
converter efficiency
closed loop regulation performance
Prof R T Kennedy

35. INDUCTOR CURRENT v INDUCTANCE
DswT
Dfwd T
Iout
Ein-Vout
-Vout VL IL t
REDUCTION in L
constant duty cycle
Prof R T Kennedy

36. INDUCTOR CURRENT v INDUCTANCE
increased
Isw,max
Ifwd,max
IC,ripple
Vout,ripple
REDUCTION in L
DswT
Dfwd T
Iout
Ein-Vout
-Vout VL IL t
constant duty cycle
Prof R T Kennedy

37. INDUCTOR CURRENT
Prof R T Kennedy

38. variable duty cycle INDUCTOR CURRENT Dsw > 0.5 IL Dsw= 0.5 IoutIL t
Iout
Dsw = 0.2
Dsw = 0.5
Dsw = 0.8
Dsw > 0.5
Dsw < 0.5
Dsw= 0.5
Prof R T Kennedy

39. LOAD (R) INDEPENDENT INDUCTOR CURRENT DOWNSLOPE UPSLOPE IL tt
Prof R T Kennedy

40. INDUCTOR PEAK-PEAK RIPPLE CURRENT
Prof R T Kennedy

41. CCM-DCM BOUNDARY
Prof R T Kennedy

42. CCM-DCM BOUNDARY
boundary
Prof R T Kennedy

43. CCM-DCM BOUNDARY
CCM
boundary
DCM
Prof R T Kennedy

44. CCM-DCM BOUNDARY L Dsw fsw constant CCM CCM / DCM determined by R DCM
INCREASE R
‘light loading’
DCM
to ensure a desired CCM
does not transfer to DCM
specify a minimum load current (maximum R)
avoid open circuit operation
Prof R T Kennedy

45. CCM / DCM determined by L
CCM-DCM BOUNDARY
R Dsw fsw
constant
CCM
CCM / DCM determined by L
DECREASE L
DCM
to ensure a desired CCM
does not transfer to DCM
design for CMM
at lowest inductance
including  L v  I
Prof R T Kennedy

46. CCM / DCM determined by fsw
CCM-DCM BOUNDARY
R Dsw fsw
constant
CCM
CCM / DCM determined by fsw
DECREASE fsw
DCM
to ensure a desired CCM
does not transfer to DCM
design for CMM
at lowest frequency
Prof R T Kennedy

47. CCM / DCM determined by Dsw
CCM-DCM BOUNDARY
L R fsw
constant
CCM
CCM / DCM determined by Dsw
DCM
to ensure a desired CCM
does not transfer to DCM
design for CMM
at lowest duty cycle
DECREASE Dsw
Prof R T Kennedy

48. DCM lower control range LINE & LOAD REGULATION DCM CCM
Prof R T Kennedy

49. DCM lower control range LINE & LOAD REGULATION DCM CCM
Prof R T Kennedy