Low Voltage Power Supply Filter Box - Home | CTIO Voltage Power Supply Filter Filter Box Revision...

2011‐02‐23

1 Filter Box Operating and Service Manual.doc

Operating and Service Manual

Front End Electronics Crate

Low Voltage Power Supply Filter

Filter Box Revision – D

2011‐02‐23


TABLE OF CONTENTS

Contents SPECIFICATION ........................................................................................................................................................................ 5

Monitor Port ........................................................................................................................................................................... 7

Input Output Terminals ........................................................................................................................................................... 8

THEORY of OPERATION ......................................................................................................................................................... 10

Filter Frequency Response .................................................................................................................................................... 12

Assembly Notes: .................................................................................................................................................................... 13

Primary Shield/Cover Removal ............................................................................................................................................. 13

Primary Shield/Cover Replacement ...................................................................................................................................... 13

PCB Assembly ........................................................................................................................................................................ 14

Schematic .............................................................................................................................................................................. 15

Single Filter Section ............................................................................................................................................................... 16

Mechanical Drawings ............................................................................................................................................................ 24

Bill Of Materials ..................................................................................................................................................................... 25

APPENDIX .............................................................................................................................................................................. 26

Title Document # ............................................................................................................................................................... 26

Figure 1: Filter Box with Primary Shield removed .................................................................................................................. 3

Figure 2: Filter with Primary Cover Installed .......................................................................................................................... 4

Figure 3 Filter Box Monitor Port Pinout .................................................................................................................................. 7

Figure 4 Filter Box PCB Top ..................................................................................................................................................... 8

Figure 5 Vicor OUT to Filter IN ................................................................................................................................................ 8

Figure 6 Filter Box OUT to Analog Backplane with G10 Cover installed ................................................................................. 9

Figure 7: Single Filter Schematic ........................................................................................................................................... 10

Figure 8: Typical Ripple reduction with current increase. .................................................................................................... 11

Figure 9: Attenuation ............................................................................................................................................................ 12

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Figure 1: Filter Box with Primary Shield removed

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Figure 2: Filter with Primary Cover Installed

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SPECIFICATION

• Eight (8) Independent channels

• Voltage Rating 100V

• Current Rating 15A

• Resistance (each leg) 13 to 19 milliOhms

• Attenuation Common & Differential Modes45db/decade starting at 30KHz

• Monitor Port 2.00V @ Normal Operating Levels

o 8 Analog Channels

o 1 Over Temperature Switch

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o GENERAL INFORMATION

The Filter Box is designed to be part of the Low Voltage Power Supply for the Front End Electronics (FEE) and Heater Crates. The filter removes most of the switching noise produced by the commercial Vicor power supply. The Filter Box also provides a voltage monitor port and over temperature signal for the Internal Crate Controller (ICC). The over temperature switch closes a 60°C.

The FEE crates require eight (8) voltage rails, two for digital and six for analog circuitry. The Heater crates require four (4) rails, two for control circuits and two for power circuits. Each rail has its own filter and each filter is electrically identical.

The filter uses feed‐through capacitors for input and output connections to the main box. The main box is a Faraday shield. The top, bottom and center layers of the circuit board will act as EMI shields and will be connected to chassis ground. Each filter section or channel within the box has individual shields. The box dimensions are approximately 12”x6”x0.75”. The box is mounted directly to the Vicor power supply. The outputs of the Vicor connect directly to the inputs of the filter box. The output of the Filter Box connects directly to the Analog Backplane that distributes power to the Front‐End Electronics Transition cards.

The filter is a differential /common mode filter and all components are rated to handle a minimum of 15 Amps continuous.

Thermal management is handled by conduction from components to the PCB, then from secondary shield through thermal pad to the primary shields attached to the Vicor chassis.

PCB Details:

• The PCB will require a minimum of 8 layers. Power plane layer require 2 ounce copper while all other layers can be 1 ounce.

• The PC board itself will act as one side of the EMI chassis of the Filter Box. • All electrical connections into and out of the Filter Box are made through filtered barrier strips. • Power planes will transfer the voltages to and from the individual filters. • Inputs (noisy) to and Outputs (quiet) from the filter box will be separated by the center ground plane.

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Monitor Port This port provides a way to monitor the output voltages of the Filter Box. The signals are current limited and scaled such that at normal operating voltages the output is 2.00 volts.

Figure 3 Filter Box Monitor Port Pinout

+++

+

+

++

+

++

Blue ovals indicate Heater Monitoring

Red ovals indicate Front End Electronics Monitoring

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Input Output Terminals The Filter Box is installed on the Vicor supply so the terminals on the end are above the supply terminals. We are trying to make the wiring short in length.

Figure 4 Filter Box PCB Top

Figure 5 Vicor OUT to Filter IN

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Figure 6 Filter Box OUT to Analog Backplane with G10 Cover installed

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THEORY of OPERATION Several conditions require the use of switching power supplies in the DECam project. The primary restriction is the limited space available. Switching supplies are however inherently noisy and cannot be uses with sensitive electronics without removing as much switching noise as possible.

The filter box uses a standard differential and common mode filter arrangement. The lowest current component can handle a maximum current of 19Amps.

Figure 7: Single Filter Schematic

Measurements show that the Vicor supply produces larger amounts of common‐mode noise than differential‐mode noise. The filter addresses both issues.

The filter box is a six sided enclosure that forms a Faraday shield. The box is electrically tied to the Vicor chassis allowing the common mode noise to return to the source (Vicor outputs) as quickly as possible. Inputs to the box are minimum length twisted pairs. Output lengths are also minimized going directly to the Analog Backplane.

Each output from the Vicor is isolated until it reaches the Analog backplane. There all the returns are connected together and through a large braid tied to the FEE crate chassis. This is our single point star connection. Any other connections of the power rails will form a ground loop and must be avoided.

The common mode choke inside the filter must have current flowing to work properly. In fact the more current that flows the better the filter works. There is a tradeoff between the maximum current and the inductance of the choke.

Figure 8 shows a typical reduction in noise ripple from no current on the top trace to 5 Amps on the bottom trace in 1 Amp steps.

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Figure 8: Typical Ripple reduction with current increase.

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Filter Frequency Response

Figure 9: Attenuation

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Assembly Notes: There are a few procedures that must be preformed to yield a box that will fit properly into the final FEE crate.

Primary Shield/Cover Removal The primary shield and PCB are held together by 16 brass screws, two on each of the terminal blocks. These screws sandwich the shield between the terminal block and its mounting bracket. The Primary shield has slotted holes so they only need to be loosened to remove the cover. There is also two nuts on the subminiature ‘D’ connector that need to be removed before the shield can be separated from the PCB. At this point the shield will be held by the EMI fence on the monitor end (‘D’ sub) and in the space on each side. It is best to pry the cover off with a screwdriver to avoid bending it or the fencing.

Primary Shield/Cover Replacement Assembling the Primary shield/cover requires some adjustments to ensure proper fit with the mounting brackets. The thermal pads on the Secondary shields press against the Primary shield and must be compressed slightly during assembly. The Primary shield is first attached to the Vicor top. Next the PCB is carefully positioned so all the fingers on each EMI fence engage before seating the four mounting bracket stops to contact the cover.

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PCB Assembly

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Schematic

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Single Filter Section

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Data Sheets

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Mechanical Drawings

DES FRONT END DC FILTER BOX SCHEMATIC/PCB ED‐173687‐1/2

DES FRONT END DC FILTER BOX ASSEMBLY MD‐173688‐A

DES FRONT END DC FILTER BOX PRIMARY EMI SHIELD MD‐173689‐D

DES FRONT END DC FILTER BOX EMI 1.5IN 3‐PIN FENCE MD‐173690‐1



DES FRONT END DC FILTER BOX BARRIER STRIP BRACKET MD‐173692‐D

DES FRONT END DC FILTER BOX PCB MOUNTING BRACKET MD‐173693‐D

DECAM FRONT END ELECTRONICS FITLER BOX G10 INSULATOR MD‐173735‐1

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Bill Of Materials

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APPENDIX

Other documents available on DES Document Database http://des‐docdb.fnal.gov:8080/

Title Document #

Vicor Filtering for Monsoon Crate Use 765

Vicor Switching Supply Noise Studies 902

DECam‐Vicor Filter Box 1969

Master Reference List ‐ Power Supply Filter Box 2932

Power Supply Filter Box Testing 2927

Power Supply Filter Box 1380

ICC Front End Electronics Over Voltage Circuit 4264

DECam‐Vicor Filter Box Testing 4379

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