Powere Lab An Active EMI reduction IC WT

Powere. Lab An Active EMI reduction IC WT 6001 POWERELAB LIMITED A Power Converter Technology Provider Power. ELab Limited www. powerelab. com 1

EMI in switching power supplies Powere. Lab n n All products must comply with various EMI regulations EMI reduction in switching power supply is mainly carried out by passive filters n n n Power. ELab Limited filter chokes are big and dissipative Y capacitors introduce leakage current It is desired to cut down filter requirement www. powerelab. com 2

Powere. Lab n n n An active EMI IC is introduced EMI reduction by active method It cuts down common mode current in SMPS A small SO 8 IC that n n n Power. ELab Limited cuts down common mode choke size reduces Y capacitor requirement eliminates thermal problem in common mode chokes increase SMPS overall efficiency reduces product cost www. powerelab. com 3

Powere. Lab Common mode current in SMPS n n 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 Power e. Lab Power. ELab Limited www. powerelab. com 4

Powere. Lab Generation of common mode current in SMPS & the IC Load LISN spectrum Power. ELab Limited www. powerelab. com 5

Safety requirement and EMI limits Powere. Lab n n Power. ELab Limited 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 www. powerelab. com 6

The IC provides an effective Y -cap booster Powere. Lab n n n n Power. ELab Limited 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 – 800 Hz) 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 EN 61000 -4 -4 and EN 61000 -4 -5 immunity standard Independent of converter power level, it can handle high power converters www. powerelab. com 7

Powere. Lab An application example – 120 W power adaptor n n The original EMI filter design cannot pass the EN 55022 class B limit Filter component: 2 x 20 mm high mu toroid 2 x 0. 15 u. F X – cap 1 x 1 n Y 1 -cap Power. ELab Limited www. powerelab. com 8

Powere. Lab n n n Original filter circuit It is a commonly used filter configuration L 2 B is wound with many turns which intends to suppress the low to mid-frequency common mode noise. Its leakage inductance together with C 1 also provides differential mode noise filtering L 1 B is a single layer, bi-filer wound common mode choke for high frequency common mode noise filtering Power. ELab Limited www. powerelab. com 9

Powere. Lab EMI measured results – Original design high line low line n n n At 230 Vac 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 Power. ELab Limited www. powerelab. com 10

EMI solution – A better one using Y-cap booster Powere. Lab n n Y-cap booster is used to replace the 1 n Y-cap In addition to the removal of L 2 B, L 1 B can be further reduced to a 9 mm toroid with only a few turns Power. ELab Limited www. powerelab. com 11

Powere. Lab Filter size reduction Failed design even with more cost, loss and bigger size for the filter Power. ELab Limited Passed design using Y-cap booster with much smaller filter size that saves cost, power and space www. powerelab. com 12

Powere. Lab Filter comparison Y-cap booster demo board Power. ELab Limited www. powerelab. com 13

Summary Powere. Lab n n n 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 Power. ELab Limited www. powerelab. com 14

Powere. Lab The IC WT 6001 • 8 pin SO IC Power. ELab Limited PIN Function 1 NC 2 GND, ref to Vcc 3 NC 4 NC 5 Out, to Y cap 6 Vcc, max 15 V 7 Ref, set bias point 8 In, feedback pin www. powerelab. com 15

Observation of cancellation by an oscilloscope Powere. Lab § A very useful way to observe the effectiveness of cancellation is by probing the waveform across the primary & secondary Floating oscilloscope Power. ELab Limited www. powerelab. com 16

Powere. Lab Observation of cancellation by an oscilloscope § Waveforms observed before & after application of the EMI IC A 1 n. F Y-cap across primary & secondary Power. ELab Limited EMI IC circuit across primary & secondary www. powerelab. com 17

Powere. Lab Waveform shows cancellation effect § Class II – no ground connection, Y-cap only Waveform across primary & secondary Power. ELab Limited High noise level www. powerelab. com 18

Powere. Lab Waveform shows cancellation effect § Class II – no ground connection, EMI IC applied Upper Ch : Waveform across primary & secondary Lower Ch : IC output Power. ELab Limited Low noise level www. powerelab. com 19

Powere. Lab Waveform shows cancellation effect § Class I –ground connection, Y-cap only Upper Ch : Waveform across primary & secondary Power. ELab Limited High noise level www. powerelab. com 20

Powere. Lab Waveform shows cancellation effect § Class I – ground connection, EMI IC applied Upper Ch : Waveform across primary & secondary Lower Ch : IC output Power. ELab Limited Low noise level www. powerelab. com 21

Powere. Lab Procedures to implement the IC to a switching power supply Make sure that there is enough differential mode choke. Differentiate between Class I & Class II products to see whether the IC can apply 1. 2. a. b. 3. 4. Power. ELab Limited Class I product – Put a big capacitor between the primary & secondary Class II product – Short circuit the primary & secondary If there is significant reduction in common mode noise on the spectrum, apply the Class I or Class II circuit accordingly. Put in small common mode choke for high frequency noise suppression. The IC works up to 7 MHz. www. powerelab. com 22

Trimming process Powere. Lab § 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 Power. ELab Limited www. powerelab. com 23

Points to note Powere. Lab § The IC works best when Vcc is close to 15 V § The power supply should be properly laid out for best effect Power. ELab Limited www. powerelab. com 24

Powere. Lab Question & Answers Power. ELab Limited www. powerelab. com 25