GB2222726A

GB2222726A - Printed circuit boards

Info

Publication number: GB2222726A
Application number: GB8821072A
Authority: GB
Inventors: Brian Purdy Goddard; David John Pearce
Original assignee: Racal Milgo Ltd
Current assignee: Racal Milgo Ltd
Priority date: 1988-09-08
Filing date: 1988-09-08
Publication date: 1990-03-14
Also published as: WO1990003101A1; EP0403602A1; GB8821072D0

Abstract

A printed circuit board (10) slides into a rack and has means (11) mounted along the rear edge of the board (10) for effecting plug-in connection to the back plane of the rack. First (12) and second (13, 14) conductive tracks extend along the side edges and constitute two power supply rails serving components mounted on the board (10). The rack has first and second guides into which the side edges of the board slide, and complementary means for effecting the plug-in connection to the means (11). The guides include conductive parts which make electrical contact with respective tracks (12, 13, 14) for supplying power thereto. Preferably one track (12) extends nearer to the rear edge than the second track (13, 14), which is divided into a track (14) near the front edge of the board and another track (13) connected through a resistor (20) to the track (14) near the front edge of the board.

Description

IMPROVEMENTS RELATING TO PRINTED CIRCUIT BOARDS This invention relates to removable printed circuit boards, particularly but not exclusively large, complex boards making many connections to the back plane of a unit.

Although connections may be made via tracks on the board itself, the edge of the board plugging into an edge connector, when large numbers of connections are involved it is customary to use connectors having multiple rows of pins or sockets (hereinafter reference is made to pins for simplicity), e.g. DIN 4162 96 way connectors having three rows of 32 pins. The pins in such connectors are necessarily quite fine and if these pins are to be used for carrying power to the board, a plurality of pins have to be parallelled up to provide adequate current carrying capacity. This is not only wasteful use of pins but potentially unreliable. It also suffers from the problem that the power supply connections are made at the same time as the signal connections.

There are many situations in which it is desirable to be able to insert and remove cards from a unit without switching off the power supply (live board exchange). This is only possible if the card in question powers up correctly on insertion and if insertion and removal do not create disturbances which interfere with the operation of other cards.

Various proposals are known for ensuring that power supply connections are made before signal connections, including the use of extended power supply pins or extended power supply tracks on the edge of the printed circuit board. All such proposals rely upon specialized back planes or connectors. It is the object of the present invention to provide a solution to the problem which readily gives high current carrying capacity and moreover, as explained below, can be developed to give improved, controlled power up/power down sequences on insertion or removal of boards.

The invention is defined with particularity in the appended claims. An embodiment of the invention will be described in detail, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a plan view of a printed circuit board, and Fig. 2 is a section to a larger scale through one edge of the board in its guide rail.

Referring to Fig.l the printed circuit board 10 has a plurality of connectors 11 mounted along its rear edge for plug-in connection in conventional manner to complementary connectors on the back plane of a rack. The rack can be essentially conventional, apart from its guide rails and is therefore not illustrated. It may accommodate a substantial number of printed circuit boards (cards) slid into the rack parallel to one another.

The pins of the connectors 11 are connected to the printed circuit board tracks and vents to the various components mounted on the board. The power supply for the components is not provided through the connectors 11. For this purpose, use is made of conductive tracks provided along the side edges of the board on at least one side thereof. As illustrated in Fig.1 there is an extended track 12 running almost the length of the lefthand edge of the card. In this example this is the OV rail of the card. The track 12 extends near to the back of the board.

On the righthand edge of the board there is a short track 13 towards the rear of the board and a longer track 14 at the front of the board. These tracks form the "live" power supply rail, e.g. a 5V rail.

Turning to Fig.2 there is shown a portion of the bottom wall 15 of a rack into which the cards are inserted lying in spaced, parallel, planes. Mounted on the inside of the wall 15 is a guide rail 16 for slidably receiving one edge of the card 10. This guide rail is formed from insulating material housing a resilient metal channel 18 having a metal tongue or tongues 19 such that the printed circuit board can be slid into the channel to be gripped reasonably firmly therein. The tongue(s) 19 moreover make good electrical contact with the corresponding conductive track, e.g. the track 12, on the edge of the board. The insulator is attached to the wall in any convenient manner, e.g. by rivets (not shown) through the base of the insulator registering with holes in the base of the metal channel 18, such that the latter is not shorted to the wall 15.

The channels 18 on the two edges of the printed circuit board are utilized as the means for conducting power to the board and are thus connected in this example to the OV and 5V terminals respectively of a power supply. When the card is slid into the rack, the OV track 12 initially makes contact with the OV channel 18, because this track 12 extends well towards the back of the boards. The first operation on insertion therefore, in electrcal terms, is to establish signal ground throughout the board. The first 5V track 13 (Fig.1) terminates a greater distance from the rear of the board than the track 12. Accordingly +5V is applied to the track 13 after OV has been applied to the track 12.The 5V track 13 is connected to the components on the board 10 through a current limiting circuit 20 which serves to reduce the initial surge of current drawn by the card as the various capacitances thereon are charged up. This reduces the risk that the inserted card will cause a disturbance on the power supply sufficient to upset the operation of cards already inserted in the rack.

Further insertion of the card brings the second 5V track 14 into contact with the 5V channel 18 and +5V is applied directly thereby to the components on the card. To exercise further control over the powering up of the card more than two +5V tracks may be provided. The final track will apply 5V direct; the preceding tracks will apply 5V through a series of current limiting circuits.

The invention is particularly suitable for cards requiring only a single voltage in addition to OV. By varying the channels and conductive track pattern on the board, additional voltage rails could be accommodated. The use of OV and 5V rails are shown by way of example. Any safe low voltage (either AC or DC) may be used with appropriate rectification, smoothing and regulation being on the board.

The conductive channels 18 in the rack are all permanently energised and it is intended that the insertion or removal of one card will not interfere with the running of the other cards in the rack. An additional benefit with the method of power application is that signal lines can be suitably set prior to insertion into the signal connectors.

If required, PCB self diagnostics can be carried out prior to insertion into the signal connectors. Mechanical interlocking could be employed to prevent a faulty card reaching the signal connectors.

Claims

CLAIMS:

1. A printed circuit board having front and rear edges and first and second side edges, means for effecting plug-in connection to the back plane of a rack mounted along the rear edge of the board and first and second conductive tracks extending along at least one of the side edges and constituting two power supply rails serving components mounted on the board.

2. A printed circuit board according to claim 1, wherein the first and second tracks extend along the first and second side edges respectively.

3. A printed circuit board according to claim 1 or 2, wherein the first track extends nearer to the rear edge than the second track.

4. A printed circuit board according to claim 1, 2 or 3, wherein the second track is divided into a plurality of tracks including a track near the front edge of the board and at least one other track, the or each other track being connected through a resistor to the track near the front edge of the hoard.

5. A printed circuit board according to claim 4, wherein the said track near the front edge of the board is longer than the or each other track.

6. A printed circuit board according to any of claims 1 to 5, wherein at each side edge of the board corresponding and electrically connected tracks are provided on the two faces of the board.

7. A printed circuit board according to any of claims 1 to 5, wherein at at least one side edge of the-board separate tracks are provided on the two faces of the board to form two different power supply rails.

8. A printed circuit board according to any of claims 1 to 7 in combination with a rack having first and second guides into which the first and second side edges respectively on the board slide, at least one guide including at least one conductive part which makes electrical contact with a respective one of the said tracks for supplying power thereto.

9. A printed circuit board and rack according to claim 8, wherein each guide comprises a conductive channel member in which the corresponding side edge of the board slides.

10. A printed circuit board and rack according to claim 9, wherein the channel member is housed in an insulating channel.

11. A printed circuit board and rack according to claim 8, 9 or 10, wherein the channel member is divided into two electrically separated parts contacting tracks on opposite sides of the board.

11. A printed circuit board and rack according to claim 9 or 10, wherein the channel member has resilient tongues bearing on at least one face of the board.

12. A printed circuit board and rack according to claims 9, 10 or 11, wherein the channel member is divided into two electrically separated parts contacting tracks on opposite sides of the board.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS 1. A printed circuit board and a rack into which the board slides, the printed circuit board having front and rear edges and first and second side edges, means for effecting plug-in connection to the back plane of the rack mounted along the rear edge of the board and first and second conductive tracks extending along at least one of the side edges and constituting two power supply rails serving components mounted on the board, the rack having first and second guides into which the first and second side edges respectively on the board slide, and complementary means for effecting the said plug-in connection, at least one guide including at least one conductive part which makes electrical contact with a respective one of the said tracks for supplying power thereto.

2. A printed circuit board and rack according to claim 1, wherein the first and second tracks extend along the first and second side edges respectively.

3. A printed circuit board and rack according to claim 1 or 2, wherein the first track extends nearer to the rear edge than the second track.

4. A printed circuit board and rack according to claim 1, 2 or 3, wherein the second track is divided into a plurality of tracks including a track near the front edge of the board and at least one other track, the or each other track being connected through a resistor to the track near the front edge of the board.

5. A printed circuit board and rack according to claim 4, wherein the said track near the front edge of the board is longer than the or each other track.

6. A printed circuit board and rack according to any of claims 1 to 5, wherein at each side edge of the board corresponding and electrically connected tracks are provided on the two faces of the board.

7. A printed circuit board and rack according to any of claims 1 to 5, wherein at at least one side edge of the board separate tracks are provided on the two faces of the board to form two different power supply rails.

8. A printed circuit board and rack according to any of claims 1 to 7, wherein each guide comprises a conductive channel member in which the corresponding side edge of the board slides.

9. A printed circuit board and rack according to claim 8, wherein the channel member is housed in an insulating channel.

10. A printed circuit board and rack according to claim 8 or 9, wherein the channel member has resilient tongues bearing on at least one face of the board.