Power Power e Lab Lab PowerELab Limited PowerELab Limited www.powerelab.com www.powerelab.com 1 An Active EMI reduction IC WT6001 POWERELAB LIMITED A Power Converter Technology Provider
Aug 23, 2014
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 11
An Active EMI reduction ICWT6001
POWERELAB LIMITEDA Power Converter Technology Provider
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 22
EMI in switching power supplies
All products must comply with various EMI regulations
EMI reduction in switching power supply is mainly carried out by passive filters filter chokes are big and dissipative Y capacitors introduce leakage current
It is desired to cut down filter requirement
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 33
An active EMI IC is introduced
EMI reduction by active method It cuts down common mode current in SMPS A small SO8 IC that
cuts down common mode choke size reduces Y capacitor requirement eliminates thermal problem in common mode chokes increase SMPS overall efficiency reduces product cost
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 44Power eLab
Common mode current in SMPS
Common mode current is a major contributor of conducted EMI
It is difficult to trace as its path is not readily seen on a circuit diagram
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 55
Generation of common mode current in SMPS & the IC
LISN Load
spectrum
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 66
Safety requirement and EMI limits
The added Y-cap can effectively reduce the common mode current due to the parasitic capacitance of the load to the earth
The maximum allowed value is limited by the leakage current requirement
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 77
The IC provides an effective Y-cap booster
Equivalent to a Y-cap with very large value within the EMI concerned frequency range only
Capacitance remains low in the leakage current test frequency range (50 – 800Hz)
Provide effective EMI solution Greatly reduce the common mode filter requirement Reduce converter size and improve conversion efficiency Built-in electrical voltage surge protection which can
easily pass EN61000-4-4 and EN61000-4-5 immunity standard
Independent of converter power level, it can handle high power converters
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 88
An application example – 120W power adaptor
The original EMI filter design cannot pass the EN55022 class B limit
Filter component:2 x 20mm high mu toroid 2 x 0.15uF X – cap1 x 1n Y1-cap
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 99
Original filter circuit
C2
L2B
13
24
C1
L1B
13
24
P1
1
P2
1
TH1 F1
It is a commonly used filter configuration
L2B is wound with many turns which intends to suppress the low to mid-frequency common mode noise. Its leakage inductance together with C1 also provides differential mode noise filtering
L1B is a single layer, bi-filer wound common mode choke for high frequency common mode noise filtering
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1010
EMI measured results – Original design
100V pri-sec Y1n U shielded originalEN 55022; Class B Conducted, Quasi-Peak
EN 55022; Class B Conducted, Average
0
10
20
30
40
50
60
70
80
1 10
dBuV
10/3/2005 11:00:49 (Start = 0.15, Stop = 30.00) MHz
230V pri-sec Y1n U shielded original
EN 55022; Class B Conducted, Average
EN 55022; Class B Conducted, Quasi-Peak
0
10
20
30
40
50
60
70
80
1 10
dBuV
10/3/2005 10:55:40 (Start = 0.15, Stop = 30.00) MHz
At 230Vac input, detailed measurement showed that the circled regions can only marginally pass or fail to meet the average limit line.
The lower frequency region seems to be caused by differential mode noise
The high frequency region is caused by common mode noise
low line high line
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1111
230V CB U shield SDMC SCMC .33uFEN 55022; Class B Conducted, Average
EN 55022; Class B Conducted, Quasi-Peak
0
10
20
30
40
50
60
70
80
1 10
dBuV
10/3/2005 16:39:55 (Start = 0.15, Stop = 30.00) MHz
EMI solution – A better one using Y-cap booster
100V CB U shield SDMC SCMC .33uF
EN 55022; Class B Conducted, Quasi-Peak
EN 55022; Class B Conducted, Average
0
10
20
30
40
50
60
70
80
1 10
dBuV
10/3/2005 16:31:32 (Start = 0.15, Stop = 30.00) MHz
Y-cap booster is used to replace the 1n Y-cap
In addition to the removal of L2B, L1B can be further reduced to a 9mm toroid with only a few turns
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1212
Filter size reduction
Failed design even with morecost, loss and bigger size for thefilter
Passed design using Y-cap booster with much smaller filter size that saves cost, power and space
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1313
Filter comparison
Y-cap boosterdemo board
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1414
Summary
Y-cap booster allow small Y-caps and meets leakage current requirement
Greatly reduce product design period and resources It can be applied to any position with conventional Y-cap Significantly reduces the size and loss of common mode
choke implies higher power density and efficiency EMI less sensitive to transformer winding capacitance
implies more rooms for improving transformer coupling Very suitable for equipment required lower leakage
current
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1515
The IC WT6001
• 8 pin SO ICPIN Function
1 NC
2 GND, ref to Vcc
3 NC
4 NC
5 Out, to Y cap
6 Vcc, max 15V
7 Ref, set bias point
8 In, feedback pin
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1616
Observation of cancellation by an oscilloscope
A very useful way to observe the effectiveness of cancellation is by probing the waveform across the primary & secondary
Floating oscilloscope
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1717
Observation of cancellation by an oscilloscope
Waveforms observed before & after application of the EMI IC
A 1 nF Y-cap acrossprimary & secondary EMI IC circuit across
primary & secondary
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1818
Waveform shows cancellation effect
Class II – no ground connection, Y-cap only
Waveform acrossprimary & secondary High noise level
115Vac final Ycap
EN 55022; Class B Conducted, Average
EN 55022; Class B Conducted, Quasi-Peak
10
20
30
40
50
60
70
80
90
1 10
dBuV
4/19/2006 4:30:16 PM (Start = 0.15, Stop = 30.00) MHz
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 1919
Waveform shows cancellation effect
Class II – no ground connection, EMI IC applied
Upper Ch : Waveform acrossprimary & secondaryLower Ch : IC output
Low noise level
115Vac Final Test
EN 55022; Class B Conducted, Quasi-Peak
EN 55022; Class B Conducted, Average
10
20
30
40
50
60
70
80
90
1 10
dBuV
4/21/2006 12:16:12 PM (Start = 0.15, Stop = 30.00) MHz
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 2020
Waveform shows cancellation effect
Class I –ground connection, Y-cap only
Upper Ch : Waveform acrossprimary & secondary High noise level
115Vac L IC Disabled EN 55022; Class B Conducted, Quasi-Peak
EN 55022; Class B Conducted, Average
10
20
30
40
50
60
70
80
90
1 10
dBuV
7/24/2006 4:12:12 PM (Start = 0.15, Stop = 30.00) MHz
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 2121
Waveform shows cancellation effect
Class I – ground connection, EMI IC applied
Upper Ch : Waveform acrossprimary & secondaryLower Ch : IC output
Low noise level
115Vac L int +BulkTx FluxBand BdFB10R
EN 55022; Class B Conducted, Average
EN 55022; Class B Conducted, Quasi-Peak
10
20
30
40
50
60
70
80
90
1 10
dBuV
7/21/2006 11:57:28 AM (Start = 0.15, Stop = 30.00) MHz
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 2222
Procedures to implement the IC to a switching power supply
1. Make sure that there is enough differential mode choke.
2. Differentiate between Class I & Class II products to see whether the IC can apply
a. Class I product – Put a big capacitor between the primary & secondary
b. Class II product – Short circuit the primary & secondary
3. If there is significant reduction in common mode noise on the spectrum, apply the Class I or Class II circuit accordingly.
4. Put in small common mode choke for high frequency noise suppression. The IC works up to 7 MHz.
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 2323
Trimming process
To cater for different power supply environment, the following components can be trimmed Y-cap connected to the IC output (pin 5) Feedforward resistors in the circuit for
class I products Refer to datasheet for details
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 2424
Points to note
The IC works best when Vcc is close to 15V
The power supply should be properly laid out for best effect
PowerPowereeLabLab
PowerELab LimitedPowerELab Limited www.powerelab.comwww.powerelab.com 2525
Question & Answers