1.Why is an EMI filter (AC line filter) needed in power supplies? AC line filters' primary function is to suppress the conducted emissions (noise) generated by a power converter to enter the AC mains lines. The line filter must be able to suppress the conducted emission to a sufficiently low level to pass the regulatory limits (e.g., FCC part 15). A product not complied with the regulatory requirements will not be allowed to launch to the market. 2.What does the AC line filter do in a power supply? An AC line filter can suppress both the differential-mode and common-mode noises in the conducted missions. According to the nature of the noises, conducted emissions can vastly divide into two types: Common-mode noise Differential-mode noise Generally, the common-mode noises are suppressed by the L-C filter, which consists of a common-mode choke(s) and Y-capacitors. In contrast, differential-mode noises are suppressed by the L-C filter consists of a differential-mode inductor(s) and X-capacitors. The leakage inductance of the common-mode choke is usually used in place of an individual differential-mode inductor to reduce component count. 3.What is the GT AEF (Active EMI Filter) module? The GT AEF module is an active power filter explicitly designed to cancel differential-mode conducted emissions at minimum power loss and heat generation. Compared to the conventional passive EMI filtering solutions, the GT AEF module's power dissipation is a lot lower, which implies improvements in system power efficiency and power density. 4.What is the difference between the passive EMI filter and the GT AEF solution? The conventional passive EMI filters and GT AEF solution's primary function is the same, which is to reduce conducted emissions to a sufficiently low level to meet regulatory requirements. The GT AEF solution is a filter that presents a very high impedance to the AC mains network in a specific range of frequency. The main differences between the two solutions are: Passive EMI filter GT AEF solution Architecture Single or multiple stage L-C filter Single-stage active filter Design / Engineering time Long and iterative Short Output impedance Fixed profile against noise frequency High impedance throughout a specific range of frequency DC supply voltage Not required 12V DC Physical size Bulky Relatively compact Weight Heavy Relatively lighter Total power dissipation High (typically 5W for a 2kW system) Low (typically <2W for a 2kW system) 5 .What is the limitation of the GT AEF solution? The maximum loading power of the GTAEF module is defined by the maximum RMS loading current at a 220V AC supply voltage. Thus, the maximum loading power of a 2kW AEF module will be reduced to 1kW at a 110V AC supply voltage due to the limited maximum loading current of the AEF module. The AEF-20S can support up to 2kW loading power for 220VAC mains systems. For 110VAC mains voltage, the maximum loading power will reduce to 1kW as the loading power limit is defined by the maximum loading current of the AEF module. The maximum voltage of the noise source must not exceed 2Vp-p. An external input capacitor is needed to reduce the noise voltage swing if the magnitude is higher than 2Vp-p. The DC supply voltage to the AEF module should be acquired from the power supply's primary side. 6 . What is the suggested DC power source for powering the GT AEF module? The AEF module accepts a 12V to 15V DC supply voltage to support its operation. Since the high voltage connections and the DC power supply inputs are isolated electrically, the DC voltage from the auxiliary winding (at the power side) of the power supply is a suitable voltage source for the AEF module. 7. Can the AEF module be used in DC power systems? Yes. The GT AEF module can fit in DC or AC power systems. 8. Can the AEF-20S be used in low power consumption systems, e.g., 200W application? Yes. The GT AEF module functions good in low power applications and still helps shorten the engineering time in generating EMI solutions. 9.Can the GT AEF module reduce the radiated emissions of a power supply? No, the GT AEF module can reduce conducted emissions only. Radiated emissions are usually related to the design of PCB layout, casing design, and mode of operation of the power supply. (e.g., hard-switching generates more radiated emissions than soft-switching does) 10.Can the GT AEF module be shut down as needed to allow extreme power saving? Yes. The GT AEF module can be shut down by pulling the EN pin voltage to below 3.5V. 11.Will the operation of the power supply be affected after shutting down the GT AEF module? No. Shutting down the AEF module will cease the active suppression of conducted emission but will not affect the power supply's operation. 12.What is the consequence of exceeding the rated limits of the GT AEF module? Operating the AEF module with the rated limits exceeded could cause permanent damage to the AEF module but will not damage the core circuit of the power supply.

FAQs - Galaxy Tech Limited

1.Why is an EMI filter (AC line filter) needed in power supplies?

AC line filters’ primary function is to suppress the conducted emissions (noise) generated by a power converter to enter the AC mains lines. The line filter must be able to suppress the conducted emission to a sufficiently low level to pass the regulatory limits (e.g., FCC part 15). A product not complied with the regulatory requirements will not be allowed to launch to the market.

2.What does the AC line filter do in a power supply?

An AC line filter can suppress both the differential-mode and common-mode noises in the conducted missions. According to the nature of the noises, conducted emissions can vastly divide into two types:

Common-mode noise
Differential-mode noise

Generally, the common-mode noises are suppressed by the L-C filter, which consists of a common-mode choke(s) and Y-capacitors. In contrast, differential-mode noises are suppressed by the L-C filter consists of a differential-mode inductor(s) and X-capacitors.

The leakage inductance of the common-mode choke is usually used in place of an individual differential-mode inductor to reduce component count.

3.What is the GT AEF (Active EMI Filter) module?

The GT AEF module is an active power filter explicitly designed to cancel differential-mode conducted emissions at minimum power loss and heat generation. Compared to the conventional passive EMI filtering solutions, the GT AEF module’s power dissipation is a lot lower, which implies improvements in system power efficiency and power density.

4.What is the difference between the passive EMI filter and the GTAEF solution?

The conventional passive EMI filters and GT AEF solution’s primary function is the same, which is to reduce conducted emissions to a sufficiently low level to meet regulatory requirements. The GT AEF solution is a filter that presents a very high impedance to the AC mains network in a specific range of frequency. The main differences between the two solutions are:

	Passive EMI filter	GT AEF solution
Architecture	Single or multiple stage L-C filter	Single-stage active filter
Design / Engineering time	Long and iterative	Short
Output impedance	Fixed profile against noise frequency	High impedance throughout a specific range of frequency
DC supply voltage	Not required	12V DC
Physical size	Bulky	Relatively compact
Weight	Heavy	Relatively lighter
Total power dissipation	High (typically 5W for a 2kW system)	Low (typically <2W for a 2kW system)

5.What is the limitation of the GTAEF solution?

The maximum loading power of the GTAEF module is defined by the maximum RMS loading current at a 220V AC supply voltage. Thus, the maximum loading power of a 2kW AEF module will be reduced to 1kW at a 110V AC supply voltage due to the limited maximum loading current of the AEF module.
The AEF-20S can support up to 2kW loading power for 220VAC mains systems. For 110VAC mains voltage, the maximum loading power will reduce to 1kW as the loading power limit is defined by the maximum loading current of the AEF module.
The maximum voltage of the noise source must not exceed 2Vp-p. An external input capacitor is needed to reduce the noise voltage swing if the magnitude is higher than 2Vp-p.
The DC supply voltage to the AEF module should be acquired from the power supply’s primary side.

6.What is the suggested DC power source for powering the GTAEF module?

The AEF module accepts a 12V to 15V DC supply voltage to support its operation. Since the high voltage connections and the DC power supply inputs are isolated electrically, the DC voltage from the auxiliary winding (at the power side) of the power supply is a suitable voltage source for the AEF module.

7.Can the AEF module be used in DC power systems?

Yes. The GT AEF module can fit in DC or AC power systems.

8.Can the AEF-20S be used in low power consumption systems, e.g., 200W application?

Yes. The GT AEF module functions good in low power applications and still helps shorten the engineering time in generating EMI solutions.

9.Can the GTAEF module reduce the radiated emissions of a power supply?

No, the GT AEF module can reduce conducted emissions only. Radiated emissions are usually related to the design of PCB layout, casing design, and mode of operation of the power supply. (e.g., hard-switching generates more radiated emissions than soft-switching does)

10.Can the GTAEF module be shut down as needed to allow extreme power saving?

Yes. The GT AEF module can be shut down by pulling the EN pin voltage to below 3.5V.

11.Will the operation of the power supply be affected after shutting down the GTAEF module?

No. Shutting down the AEF module will cease the active suppression of conducted emission but will not affect the power supply’s operation.

12.What is the consequence of exceeding the rated limits of the GTAEF module?

Operating the AEF module with the rated limits exceeded could cause permanent damage to the AEF module but will not damage the core circuit of the power supply.

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