FIELD OF THE INVENTION
This invention relates to EMI/EMC Filter Board for Power Supply and, more particularly,
for Electromagnetic protection filter circuit for power supply for avionics system.
BACKGROUND OF THE INVENTION
The power supply is a sub-assembly of all avionics systems. Its function is to convert an
aircraft 28V DC supply into different DC outputs, which are independently short circuit protected
and jointly isolated from input. The Power Supply Module contains the following:
• Filter Module
• Spike suppressors & capacitor filtering circuit
• Output Module for converting +28V DC to other Voltages (DC-DC Converter)
This Power Supply Module accepts the 28V DC aircraft supply and feed to input over
voltage protection circuit, which is protected against over voltage. After over voltage protection,
capacitor & diode are used for reducing at the noise of input supply & prevent the spikes. Then
input signal is fed to filter module. This filter module is specially designed to reduce the input
line reflected current. The module is used for protection against spikes up to ± 600V (50ohm)
source impedance. After filtering, the signals are feed to DC-DC converter.
DC-DC Converter generated outputs are passed through capacitor filter to reduce the
noise at the output.
All dc supply voltages required by avionics system are generated from 28V dc Aircraft
battery. 28V dc is passed via EMI Filter to DC-DC converter, which delivers following isolated
outputs for avionics system.
Power supply requirement complies with MIL-STD704E including emergency condition
(16V to 31.5V).
SUMMARY OF PRESENT INVENTION
The present invention, therefore, is directed to EMI/EMC Filter Board for Power Supply
for avionics system.
An aspect of the present invention is to protect the power lines from electromagnetic
Induction and protection from short circuit and overvoltage protection.
This Filter module is designed to provide protection from EMI/EMC. The components
used in this module are common mode choke, Radio Frequency Interference Filters, EMI Filters
and capacitors.
The EMI/EMC filter module is specifically designed to reduce the input line reflected
ripple current using inter point’s high frequency DC-DC converter. They are intended for use in
+16VDC to +40VDC application, which must meet MIL – STD-461 level of conducted radiated
emission. When used in conjunction with filter reduces input ripple current by 60dB at 500 KHz
and by more than 45dB at 1 MHz. This attenuation gives the converter filter combination a
performance, which exceed MIL-STD- 461 IC’s CE03 test.
The module is used for protection against spikes of up to ± 600V (50Ω source
impedance) for up to 10μsec. The 28V pass on but not be damaged by transients of ± 100V
(0.5Ω source for 100msec). The capacitor & diode are used for reducing the noise of the input
supply & prevent the spikes.
The input points of filter module is isolated from the chassis (case ground) and output of
the module (nominal voltage +28 VDC) isolated from the case ground.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the present invention become more apparent and
descriptive in the description when considered together with figures/flow charts presented:
Figure 1: is a Block Diagram of Power Supply along with EMI/EMC Filter Board
Figure 2: is a Block Diagram of EMI/EMC Filter Board for Power Supply for Avionics
System
DETAILED DESCRIPTION
Figure: 1 is a block diagram illustrating the principal components of a Power Supply with
EMI/EMC Filter Board of Avionics System. The power supply is a sub-assembly of all avionics
systems. Its function is to convert an aircraft 28V DC supply into different DC outputs, which are
independently short circuit protected and jointly isolated from input. The Power Supply Module
contains Filter Module, Spike suppressors & capacitor filtering circuit and Output Module for
converting +28V DC to other Voltages (DC-DC Converter)
This Power Supply Module accepts the 28V DC aircraft supply and feed to input over
voltage protection circuit, which is protected against over voltage. After over voltage protection,
capacitor & diode are used for reducing at the noise of input supply & prevent the spikes. Then
input signal is fed to filter module. This filter module is specially designed to reduce the input
line reflected current. The module is used for protection against spikes up to ± 600V (50ohm)
source impedance. After filtering, the signals are feed to DC-DC converter.
DC-DC Converter generated outputs are passed through capacitor filter to reduce the
noise at the output.
All dc supply voltages required by avionics system are generated from 28V dc Aircraft
battery. 28V dc is passed via EMI Filter to DC-DC converter, which delivers following isolated
outputs for avionics system.
Figure: 2 is a block diagram for EMI/EMC Filter Board. The Modules contains PI -Filter,
Radio Frequency Interference Filters, EMI Filters and capacitor network. LC filters and
Transzorbs have been incorporated at the power entry points. LC filter minimizes high
frequency coupling, thereby reducing conductive interferences. Transzorbs suppress the
transients to ensure that they do not cross the maximum rating of the devices.
Design Description:
The following parameters are taken into account while design of Filter Board:
• All the signals that enter or leave the avionics system ia passed through an EMI filter
• The EMI filter is a PI filter.
• The Circular connector is provided with a loom connection to a Female connector which
mate with a male connector on the Filter board
• The mounting-hole placement is guided by constraints of mechanical dimensions.
• Separate ground and power planes are designed to provide low impedance path to the
signals.
• High frequency signals is subjected to signal integrity analysis, and based on the
feedback, some tracks may be rerouted or termination resistances are added and tuned
to get optimum results.
• LC filters and Transzorbs have been incorporated at the power entry points. LC filter
minimizes high frequency coupling, thereby reducing conductive interferences.
Transzorbs suppress the transients to ensure that they do not cross the maximum rating
of the devices.
Specifications:
The following are the specifications:
1. Input power supply range is 16 to 40VDC. (Nominal 28VDC)
2. Line and Load Regulation: +/-1% (No Load to Full Load)
3. Ripple and Noise: 30mV P-P typical (1% maximum)
4. Short Circuit protection: Indefinite with auto recovery
5. Over voltage protection: Inbuilt Passive Transzorbs on output
6. DC Input Transient protection: MIL-STD-1275A (100V for 50ms) and MIL-STD-704D
(80V for 0.1Sec)
7. EMI/RFI: MIL-STD-461C
8. Temp Range: -55 to +85 (operation)
9. MTBF:150000Hours

WE CLAIMS:-
Accordingly, the description of the present invention is to be considered as illustrative only and is for the purpose of teaching those skilled in the art of the best mode of carrying out the invention. The details may be varied substantially without departing from the spirit of the invention, and exclusive use of all modifications which are within the scope of the appended claims is reserved. The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Function of EMI/EMC Filter Board is to reduce the input line reflected ripple current using inter point’s high frequency DC-DC converter. They are intended for use in +28VDC to +40VDC application, which must meet MIL – STD-461 level of conducted radiated emission. When used in conjunction with filter reduces input ripple current by 60dB at 500 KHz and by more than 45dB at 1 MHz. This attenuation gives the converter filter combination a performance, which exceed MIL-STD- 461 IC’s CE03 test.

2. An EMI/EMC Filter Board as claimed in any of the preceding claims wherein this accepts the 28V DC aircraft supply and feed to input over voltage protection circuit, which is protected against over voltage.

3. EMI/EMC Filter Board as claimed in any of the preceding claims wherein after over voltage protection, capacitor & diode are used for reducing at the noise of input supply & prevent the spikes.

4. EMI/EMC Filter Board as claimed in claim 3 wherein input signal is fed to EMI filter module which is specifically designed to reduce the reflected input ripple current of DC/DC converters.

5. EMI/EMC Filter Board as claimed in claim4 wherein after filtering, the signals are feed to triple output DC-DC converter (5V,? 15V), & single output (+5V excitation) DC-DC converter.

6. EMI/EMC Filter Board as claimed in claim 5 wherein a DC-DC Converter generated outputs are passed through capacitor filter to reduce the noise at the output. DC-DC converter +15V is also passed through +5V IC regulator circuit to set +5V excitation voltage.

7. EMI/EMC Filter Board as claimed in any of the preceding claims wherein line and load regulation of supply module is +/-1% (No Load to Full Load).

8. EMI/EMC Filter Board as claimed in any of the preceding claims wherein input voltage variation is 16-40V.

9. EMI/EMC Filter Board as claimed in any of the preceding claims wherein this module complied as per MIL-STD-704E

10. EMI/EMC Filter Board as claimed in any of the preceding claims wherein module ripple & noise is 30mV P-P typical (1% maximum). ,TagSPECI:As per Annexure-II