Abstract:
An IC socket is provided which has a cell acting as a back-up cell for an integrated circuit and a back-up circuit for supplying electric power of the cell to the integrated circuit.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an IC (integrated circuit) socket for mounting on printed circuit boards, low-power consuming ICs or LSIs such as CMOS memories, CMOS CPUs, or CMOS LSIs which require battery backup. 
     In an LSI memory of a microcomputer storing a program or data, a timer, a CPU or the like, the memory contents are lost or the operation is terminated upon turning off the power supply. Consequently, the operation cannot be continued after the power supply is resumed. In a device including a memory LSI, in order to prevent accidental loss of memory contents upon turning off the power supply, a backup battery is generally included so as to back up the power supply of the memory LSI. 
     In a device which is experimentally prepared or which is undergoing testing, demands frequently arise for removing a printed circuit board from a socket connected to a power supply or for removing an IC or an LSI from a socket mounted on a printed circuit board so as to replace the removed IC or LSI with a different IC or LSI. In this case, supply of (backup) power to the removed IC or LSI presents a problem. As one solution to this problem, it has been proposed to arrange a backup battery on a printed circuit board so as to allow free replacement of ICs or LSIs on the printed circuit board without a consequent termination of their functions. However, if only selected ICs or LSIs are to be selectively replaced, the power supply is disconnected, again resulting in power backup difficulty. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an IC socket which has a normal backup function as well as a function for allowing removal or mounting of ICs or LSIs from or on a printed circuit board without consequent termination of their functions, so that each IC and LSI may continue the operation it had been performing prior to its removal after it is remounted on the same or a different printed circuit board. 
     According to the present invention, an IC socket is provided comprising: an insulator consisting of an insulating material and serving as a base for an IC; a plurality of contact portions of a conductive material, which are formed in said insulator and which receive external leads of said IC; board mounting portions of a conductive material formed in said insulator in correspondence with said contact portions; a power cell arranged in said insulator; and a power backup circuit connected to said contact portions and said board mounting portions and supplying power from said power cell to said IC as a backup power supply. 
     According to the IC socket of the present invention, the replacement of ICs or LSIs which are mounted on a printed circuit board and which require power backup is facilitated. Handling and transportation of ICs and LSIs are also easy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the configuration of an IC socket according to an embodiment of the present invention; 
     FIG. 2 is a circuit diagram of a backup circuit of the IC socket shown in FIG. 1; 
     FIG. 3 is a circuit diagram showing another configuration of a backup circuit of the IC socket shown in FIG. 1; 
     FIG. 4 is a perspective view of an IC socket according to another embodiment of the present invention; 
     FIG. 5 is a circuit diagram showing a backup circuit of the IC socket shown in FIG. 4; 
     FIG. 6 is a circuit diagram showing another configuration of a backup circuit of the IC socket shown in FIG. 4; and 
     FIG. 7 is a perspective view showing the configuration of an IC socket according to still another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows the structure of an IC socket according to an embodiment of the present invention. An insulator 10 (indicated by an alternately long and short dashed line) consists of an insulating resin. A plurality of contact portions 11 (11a, 11b, . . . ) of a conductive material are formed in the insulator 10 in correspondence with the external leads of an IC or LSI. Board mounting portions 12 (12a, 12b, . . . ) are also formed in the insulator 10 in correspondence with the contact portions 11. Each contact portion 11 and the corresponding board mounting portion 12 are formed into an integral metallic pin so as to serve as a path for an input/output signal exchanged between an external lead of the inserted IC and the printed circuit board wiring connected to the portion 12. Power cells 13 (13a, 13b) and a power backup circuit consisting of diodes 14a and 14b and resistors 15a and 15b are plastic-encapsulated in the insulator 10. The cells 13a and 13b may be button-type cells such as small silver oxide cells or lithium cells, sheet-type cells, or chargeable secondary cells such as nickel cadmium cells. 
     When this IC socket is used, a general socket is first soldered on a printed circuit board. Then, the IC socket having the backup function as shown in FIG. 1 of the present invention is inserted into the general socket. Subsequently, an IC or LSI is inserted into the IC socket. When the IC is to be removed, the IC and the IC socket having the backup function are removed simultaneously from the general socket soldered on the board. 
     FIG. 2 shows an example of connections of the power backup circuit, the power cells, the contact portions 11, and the board mounting portions 12. A power supply Vcc of the contact portion 11 is connected through the anode and cathode of the diode 14a to a power supply Vcc of the board mounting portion 12 at the side of the printed circuit board. A bus line BUS, a chip select line CS, a memory write line MW, and a ground line GND between the board mounting portion 12 and the contact portion 11 are commonly connected. The positive terminal of the cell 13a is connected to the cathode of the diode 14a through the cathode and anode of the diode 14b. The negative terminal of the cell 13b series-connected to the cell 13a is connected to the ground line GND. One electrode of a capacitor 16 is common connected to the cathodes of the diodes 14a, 14b and the other electrode of the capacitor 16 is connected to the ground line GND. The resistor 15a is inserted between the cathodes of the diodes 14a, 14b and the memory write line MW, and the resistor 15b is inserted between the cathodes of the diodes 14a, 14b and the chip select line CS. The bus line BUS is a line for transmitting address signals, data signals and so on and is an input/output line which does not cause erratic operation or loss of memory contents even if a given potential is not applied to the input terminal of the IC or LSI. The diodes 14a and 14b are included so as to prevent application of a reverse voltage to the IC or LSI or short-circuiting of the cells 13a and 13b. The resistors 15a and 15b fulfill a pull-up function for the memory write line MW and the chip select line CS, respectively. The capacitor 16 accumulates charge from the printed circuit board or the cells 13a and 13b and also absorbs a spike voltage which is produced when the IC socket is removed from the printed circuit board or is connected to another printed circuit board. 
     The pin arrangement of the ICs or LSIs of CPUs or memories is standardized. Accordingly, the power supply and the input/output lines of the above configuration are connected to the board mounting portions 12 and the contact portions 11 which correspond to the pin arrangement of the CPU or memory LSI selected. 
     The mode of operation of an assembly wherein the circuit having the configuration as described above is incorporated into the IC socket will now be described. First, the external leads of an IC (or LSI) are inserted into the contact portions 11. When power is supplied from the printed circuit board, it is supplied to the IC (or LSI) through the diode 14a in the IC socket. Then, signals from the printed circuit board are supplied to the chip select line CS and the memory write line MW, and signals are exchanged between the printed circuit board and the IC side through the bus line BUS. 
     When the IC is to be temporarily removed from the printed circuit board, it is removed simultaneously with the IC socket into which the external leads of the IC are inserted. At this time, power supply to the IC from the printed circuit board is stopped. However, power is supplied to a power supply line Vcc from the power cells 13a and 13b through the diodes 14b. Due to this supply of power, signals of high level are supplied to the memory write line MW and the chip select line CS through the pull-up resistors 15a and 15b, thereby sustaining the IC in the operative mode. 
     In this manner, the power backup circuit and auxiliary power supply cells are incorporated in the IC socket. When the IC is handled as mounted on such an IC socket, the memory contents written in the IC are not lost, and replacement or transportation of ICs can be performed without problem. When a once removed IC is again mounted on the printed circuit board, it can then continue the operation it had been performing prior to its removal from the printed circuit board. With the IC socket of the present invention, the IC socket is not limited to use for a particular type of IC and can be made a general purpose IC socket. 
     FIG. 3 shows another example of the configuration of the backup circuit different from that shown in FIG. 2. The same reference numerals as used in FIG. 2 denote the same parts in FIG. 3, and a detailed description thereof will be omitted. In this example, the diode 14b shown in FIG. 2 is inserted between the power supply line Vcc of the contact portion 11 and the cathode of the diode 14a. With this configuration, the backup circuit operates in a similar manner and provides the same effect as in the circuit shown in FIG. 2. 
     FIG. 4 shows another embodiment of the present invention. In the configuration shown in FIG. 1, when the chip select line CS or the memory write line MW is grounded for some reason during the backup operation effected by means of the cells 13a and 13b, data is lost. The IC socket in FIG. 4 is designed to prevent this. Referring to FIG. 4, the same reference numerals as used in FIG. 1 denote the same parts, and a detailed description thereof will be omitted. In this embodiment, the metallic pins each consisting of an integral combination of a contact portion 11 and a board mounting portion 12 are used as stationary and movable contacts of switches SWa, SWb. The switches SWa, SWb turn on/off a chip select line CS and a memory write line MW between the board mounting portions 12 and the contact portions 11. The switches SWa, SWb are turned on/off by a press member 18 eccentrically mounted on one end of a pivot pin 17. A lever 19 is connected to the other end of the pivot pin 17. The movable contacts SWa-1, SWb-1 are connected to the stationary contacts SWa-2, SWb-2 of the switches SWa, SWb when the lever 19 is pivoted in the direction indicated by an arrow. 
     When the IC socket having the above configuration is used as mounted on a printed circuit board, the switch is turned on by the lever 19. The switch is turned off when the IC is to be removed from the printed circuit board. Then, the chip select line CS and the memory write line MW are not grounded, and data is not lost. 
     FIGS. 5 and 6 show examples of backup circuits of the IC socket shown in FIG. 4. Referring to FIG. 5, switches SWa and SWb are inserted in the chip select line CS and the memory write line MW, respectively, between the board mounting portions 12 and the contact portions 11 in the circuit shown in FIG. 2. Referring to FIG. 6, switches SWa and SWb are similarly inserted in the circuit shown in FIG. 3. 
     FIG. 7 shows still another embodiment of the present invention. In earlier embodiments, the cells 13a and 13b are plastic-encapsulated. However, in this embodiment, cells 13a and 13b are replaceable. More specifically, a cell holder 20 is arranged in an insulator 10, and the cells 13a and 13b are housed in the holder 20. A lid 21 is closed. Then, the positive terminal of the cell 13a is connected to a diode 14a, and the negative terminal of the cell 13b is connected to a ground line GND. 
     The above description has been made with reference to a backup circuit of a memory LSI. However, the present invention is not limited to this. The IC socket of the present invention may be suitably designed in accordance with any IC or LSI with which it is to be used. The elements assembled in the insulator 10 are not limited to resistors, capacitors or diodes. For example, a low-power consumption, compact, flat package-type IC may be assembled in the insulator 10. The IC socket of the present invention is not limited to a memory LSI but may be applied to a CPU or a timer IC. When the IC socket of the present invention is used for a CPU or a timer IC, removal or remounting of the IC can be performed without interrupting operation of the CPU or IC. This is particularly effective for checking printed circuit boards.