Background of the invention Improvements in laboratory techniques and practices have led to the discovery of an ever increasing number of new biomofecutes such as proteins, DNA, and other macromolecules. New protein purification and detection methods, for example, have allowed the detection of many possibly new proteins. Due to the large number of known biomolecules, it is now necessary to carry molecular comparisons of newly discovered molecules to determine to what extent they are similar to or different from known molecules. To carry out definitive analyses for proteins for example it is necessary to obtain amino acid sequence information-In order to carry out analysis of a given protein at present it is necessary to obtain the protein in substantially pure and isolated form. Electrophoresis is a well known process used in the analysis of biomolecules. There are a number of different electrophoresis processes and techniques.

It is known to use 2D PAGE gel electrophoresis to separate a sample of biomolecules into an array of separate"spots". In this technique a first dimension separation is carried out using isoelectric focussing in an immobilised pH gradient strips (also known as an IPG strip) in which the strip is re-hydrated using a solution containing the macromolecules, an electric field is applied across the IPG strip and the macromolecules are separated on the basis of pH. isoejectric focussing is carried out at high voltage, up to 10tO00 volts, and very low current, typically below 1mA for several hours. Once the first dimension separation has been completed the IPG strip is then placed in contact with a slab of gel, typically, a polyacrylamide gel and a second dimension separation is then carried out in that gel slab. Typically the second dimension separation is carried out at lower voltages but at higher currents in the range of 5mA to 100 mA. It is also known to use multi compartment

electrolysers (MCEs) to separate mixtures of proteins or other macromolecules in solution on the basis of the pH of the proteins. The result is an array of spots which can then be removed from the array and analysed by adding reagents or the like, prior to analysis by mass-spectrometry or other techniques.

However, as discussed above, there are a very large number of proteins which require analysis and identification. Existing laboratory techniques are quite labour intensive and time-consuming. There is a need to increase the throughput and productivity of electrophoresis equipment to increase throughput and attempts are being made to introduce automation into the various processes involved in the analysis of biomolecules and proteins in particular.

It would improve throughput if, for example a machine which could run one or two IPG strips at a time was able to run more, say four or six. Although some electrophoretic equipment allows the running of more than one gel at a time, the gels are run in parallel from a single channel supply. This causes problems due to the characteristics of the gels. An important aspect of running gels, particularly second dimension gels is to control the voltage and current supplied to the gel during the run. For example, when running a second dimension gel electrophoresis it might be desirable to run each gel at 250V with 250mA supplied to each gel. Thus if two gels are run in parallel, 500mA is to be supplied by the power supply at 250V. However, the characteristics including the resistance of the gels are not all identical. Thus if two gels are run in parallel one of the gels is likely to draw more current than the other. If one gel draws too much current, it can overheat and become degraded, destroying the sample and ruining the experiment and many hours or days of laboratory work, since the running of the second dimension gel is only one stage in the experimental process. If only two gels are run in parallel, the chances of one of the two gels drawing all 500mA of the current is not great. Therefore the risks of ruining the gel are not unacceptably high. However, the more gels that are run in parallel, the more chances there is of one of the gels drawing an unacceptably high current which increases the risk of destroying that gel but also perhaps ruining the other gels which may receive too little current.

Thus it is one aim of the present invention to provide a multi-channel power supply suitable for use in an electrophoresis apparatus which may be used to run multiple gels simultaneously.

One highly desirable feature of a multi-channel power supply for use in an electrophoresis apparatus is the ability to control the current/voltage supplied to the gel and in particular to control the rate at which the current/voltage rises and to set/control the maximum current/voltage per channel. For example, in some cases, it may be desirable for the voltage across. the gel to rise along a particular curve over a period of time and then stabilise whilst ensuring that the maximum current per channel does not exceed a particular value. Alternatively, it may be desirable to control the power supply so that the current changes with a particular pattern and the voltage does not exceed a particular value.

Although multi-channel power supplies are known, they suffer from a number of disadvantages which makes them unsuitable for use in an electrophoresis apparatus. A first disadvantage is that existing multi-channel power supply systems are often quite large and tend to be too large to incorporate in electrophoresis apparatus which are used in laboratories where bench space may be limited.

The second problem is that with existing multi-channel power supplies the voltage and current may suffer from a lack of controllability and are typically not computer-controllable.

It is also generally desirable for electrophoresis apparatus to be networked and controlled from a remote location. Existing multi-channel power supplies may not be suitable for use in this manner.

Further, existing multi-channel power supplies do not have the voltage and current range required for electrophoresis.

One further issue with existing multi-channel power supplies is that electrophoresis apparatus is typically used in laboratories which are typically wet environments. Any use of electrical power in such an environment has to take into account the safety issues given the likely proximity of water to the equipment.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Summary of the Invention An apparatus for performing electrophoresis, electrophoretic blotting or other applications which rely on the application of an electric field to cause the migration of biomolecules in a medium, the apparatus including a multi-channel power supply comprising a common power supply supplying DC voltage in parallel to a plurality of computer controlled conversion modules, wherein each power conversion module comprises a control means and a switch mode transformer, wherein the switch mode transformer comprises a primary winding, a secondary winding and a switching means in series with the primary winding to control operation of the power transformer in flyback mode whereby when the switching means is ON current increases in the primary winding and the energy in the transformer increases and whereby when the switching means is OFF energy in the transformer is discharged as current in the secondary, and wherein the control means controls the power transferred from the primary winding to the secondary winding by adjusting the duty cycle of the switching means.

Preferably, a computer control means is operatively connected to the power supply via opto-isolators and that computer control means may be used to control all output channels of the conversion modules.

In a preferred embodiment the apparatus includes means for monitoring the current and voltage output of the secondary winding and via closed loop control means adjusts the duty cycle of the switching means if the output voltage and/or current are outside a predefined set of parameters. Typically the closed loop control means will include a digital potentiometer or digital to analog converter (DAC).

Typically the predefined set of parameters are user defined and input into the computer control means.

It is preferred that over-current protection is incorporated in the supply.

It is a preferred feature that power supply and consumption data are collected by the computer control means in real time to enable the operating parameters of each experiment/run to be stored and graphically displayed.

In one preferred aspect a current monitoring means such as a series resistor connected to voltage threshold detector is provided in an arrangement such that if the current in the secondary exceeds a predetermined maximum,

an opto-coupler sends a signal to the control circuit to temporarily shut down the switch mode transformer.

In an alternative aspect the current drawn from the secondary is passed through a resistor of which one end is connected to a temperature-stable relaxation oscillator so that a stream of pulses is sent to an opto-coupler, with the pulse rate increasing as the output current increases, the arrangement being such that if the current in the secondary exceeds a predetermined maximum, the opto-coupler sends a signal to the control circuit to temporarily shut down the switch mode transformer.

The relaxation oscillator or voltage detector is temperature stable as a microprocessor reset/supply supervisor circuit is employed for this function In a related aspect the invention provides a multi-channel power supply comprising a common power supply supplying DC voltage in parallel to a plurality of computer controlled conversion modules, wherein each power conversion module comprises a control means and a switch mode transformer, wherein the switch mode transformer comprises a primary winding, a secondary winding and a switching means in series with the primary winding to control operation of the power transformer in flyback mode whereby when the switching means is ON current increases in the primary winding and the energy in the transformer increases and whereby when the switching means is OFF energy in the transformer is discharged as current in the secondary, and wherein the control means controls the power transferred from the primary winding to the secondary winding by adjusting the duty cycle of the switching means.

Brief Description of the Drawings A specific embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figures 1a is a circuit drawing of a common part of a multi-channel power supply embodying the present invention; Figure 1b is a circuit drawing of an interface for the power supply embodying the present invention with a computer control means; Figure 1c is a circuit drawing of the primary side of one channel of the multi-channel power supply embodying the present invention;

Figure 1 d is a circuit drawing of the secondary side of one channel of the multi-channel power supply embodying the present invention; Figure 2 schematic illustrates the operation of the switch mode transformer; Figure 3 schematically illustrates the use of MOSFET current feedback to control the current in the transformer; Figure 4 schematically illustrates the sampling of the secondary voltage at the primary of the switch mode transformer; Figure 5 schematically illustrates a reset device for signaling over- current to the control circuit via an opto-coupler ; Figure 6 is a graph illustrating the voltage supplied to a 2d Gel over a period of time; and Figure 7 illustrates a platform apparatus including a power supply embodying the present invention.

Detailed Description of a Preferred Embodiment Referring to the drawings, Figure 1a shows the common part of the power supply of a multi-channel power supply embodying the present invention which is common to ie supplies power to six conversion modules. Figures 1c and 1 d illustrate the primary and secondary sides respectively of one conversion module of which there are six in the preferred embodiment. Each conversion module provides a power supply having an output of up to 50W.

From the drawings, the construction of the power supply would be largely self evident to the person skilled in the art and therefore a detailed description of all the components and the assembly of the power supply, is not set out below. The following description largely concentrates on the unusual and novel features of the invention In the common part of the power supply AC mains current is supplied to a rectifier DB1 which charges a storage capacitor C2 to 315V. This DC voltage is supplied in parallel to six conversion modules illustrated in Figures 1c and 1d. The common part of the power supply also provides two low voltage supplies VR1 at 6V DC for the opto-couplers and DCP and Vcc at 8V DC which is used by the control circuits the SG3524 and the U7 CMOS buffers.

Each conversion module incorporates a ferrite-cored switch mode power supply transformer TR3 which as discussed below operates in flyback mode. It includes a ferrite core 104 of 11mm diameter. The core style is an ETD34.

The primary which is wound on a bobbin around the ferrite core comprises two hundred turns of 0.45mm diameter wire. The secondary which is wound around the outside of the primary also comprises two hundred turns of 0.45mm diameter wire. Insulation is provided between the primary and secondary. An air gap of 300micron sets the correct inductance and allows for energy storage.

With reference to Figure 2, in the switch mode power supply transformer the secondary is isolated from the primary. ON/OFF pulses of voltage 82 at 315V are periodically supplied to the primary 106 which ramps up the energy stored in the ferrite core while the pulse is ON. The MOSFET Q2 which is in series with the primary switches the pulse ON and OFF. When the switch is ON, the current in the winding increases through MOSFET Q2 and resistor R31 A. When the switch is OFF, the current in the winding in the core discharges through diode D3 into capacitor C18. Graph 84 illustrates the rise and fall of the core energy. Current flows in the secondary circuit charging the capacitor C18 which in turn charges capacitor C19 via a inductor LI which removes high frequency components. The polarity of the diode D3 prevents current flowing in the secondary except when the pulses are OFF.

By using a switch mode power supply, it is possible to alter the power being transferred from the primary to the secondary by altering the duty cycle of the primary winding period for which the primary pulses are ON.

In order to obtain a particular output voltage, the power supplied to the secondary circuit is controlled. As part of the control process, a sample of voltage is taken during the OFF period. The secondary voltage is sampled at the primary and referred to ground as V feedback as illustrated in Figure 5. The capacitor C14 is charged to that voltage, the current then flows in variable resistor R53. The current flowing through R53 creates a voltage which is proportional to the output voltage. A reference voltage of 2V is supplied to the control circuit SG3524. In use, the period of the voltage supply to the primary of the switch mode transformer is adjusted so that the output voltage is equal to the reference voltage, 2.0V supplied to IN+. Thus the coarse potentiometer 130 incorporating R53 is used to attenuate the feedback voltage rather than adjust the reference voltage IN+. This allows a wide range of output voltages to be supplied (over 4: 1) with no change in the common mode voltage of the reference signal IN+ at SG3524. A further potentiometer 140 is provided for

fine adjustment to increase resolution from 6 bits per potentiometer to 11 bits overall.

A further potentiometer 150 is used to give a CUTOFF command.

During an ON state the potentiometer 150 gives a 0V output. When CUTOFF is required a 6V output is supplied.

There are a number of safety features in the conversion module. If the current in the transformer gets too high, this is reflected in an increase in voltage across R31A which provides a control voltage which is input to control circuit SG3524 and switches the control circuit U4 output off temporarily. If the voltage exceeds the predetermined maximum which in the described embodiment is 250V the power supply is temporarily switched off.

There is a further safety control feature illustrated in Figure 6. A current monitor resistor is provided at the output of the secondary. Current feedback sends a current to opto-coupler U6. If the current in resistor R42 at the output in the secondary circuit, exceeds 0.3amps, current in opto-coupler U6 sends a signal to control circuit SG3524 which shuts down the control chip and transformer.

The current threshold detector U8 is temperature stable as a microprocessor reset/supply supervisor circuit is employed for this function As a safety measure, it is noted that the primary and secondary circuits of the module are entirely separate and this considerably increases the safety for the operator who is unaffected by contact with the power supply.

Figure 1 b illustrates the control bus interface to the computer control means. Opto-couplers E11, E12 and E13 allow the control circuit to be connected directly to the mains. The SDA line has two functions, sending and receiving data and is inherently at a high impedance. The input is at low impedance of 50ohms which is compatible with common coaxial leads.

A clock signal is provided by another opto-coupler U13. This system utilises the well known 12C protocol but with the send and receive line separated into two separate lines to allow the impedance to be kept at a relatively low 50ohms.

Current and voltage is monitored by a separate module also connected to the same computer control means 106.

This data is stored in the computer control means and software is provided to display the results graphically. An exemplary graph showing the voltage supplied to a 2d gel over time is shown in Figure 6.

The equipment allows several channels to be bridged together, if desired, in order to produce higher wattage, for example running larger area gels or blotting cassettes.

Figure 7 shows an overall view of a platform apparatus 100 including a multi-channel power supply embodying the present invention which provides a cooled Peltier platform divided into six areas or cells 102 which can be used to run various types of electrophoresis apparatus such as a multi compartment electrolyser (MCE) 104 which is disclosed in the applicant's PCT/AU00/01391 or a second dimension gel or an electro-blot The power supplies are provided along one side of the perimeter of the cooled platform for supplying voltage to the electrodes of the various electrophoresis apparatus/experiments.

The apparatus includes a computer control means 106 and includes a screen display 108 and a mousing pad surface 110. It is preferred that a port 112 is also provided so that a keyboard 114 can be plugged into the system to provide more complex inputs into the computer control means. The computer includes a port 120 for connection to a network such as the Internet for remote control of the platform via a computer and for accessing a database of results which may also be directly connected to the platform.

The apparatus incorporates Peltier thermoelectric modules for cooling The control system includes feedback control of the temperature in the experiments being run. The temperature of the peltiers is measured by a thermocouple or other suitable means and this information is fed back to the computer control means 106 which reduces the voltage/current supplied to the gel or other experiment in the case of overheating.

One unusual feature of the power supply of the present invention is that the output voltage from the multiple channels is negative. This enables the chassis of the electrophoresis apparatus or the like which contains the power supply to be the positive terminal, if desired.

The system incorporates a temperature sensor. This is periodically and briefly switched on to pass a fixed current of 2mA through a temperature- dependent resistance. The voltage is measured which and from this the temperature can be determined. Switching the resistor on briefly avoids heating of the resistor due to the current.

The multi-channel power supply described above provides a number of substantial advantages compared to existing electrophoresis power supplies.

In particular, individual computer control of each channel/outlet is enabled. The

opto-isolators allows the apparatus to be computer controlled by a mouse pad/ graphic display interface which is fully opto-isolated from the power supply and enables computer control and operator safety.

The use of a switch mode power supply allows the device to be relatively compact. Switch mode transformers are very efficient and relatively little energy is lost as heat. This is particularly important in the context of an apparatus for electrophoresis as the temperature of the various experiments performed on such apparatus has to be closely controlled and overheating can ruin an experiment.

The multi-channel power supply also provides for control of the individual channels by monitoring the voltage and current parameters from each cell/outlet and then via closed loop allows the adjustment of parameters to ensure that electrophoresis is completed within the user set parameters.

By using a switch mode transformer this enables the power supply to be very compact even as a multi-channel unit and to provide a wide voltage range of 50 to 200V with good efficiency The compactness enables the power supply to be incorporated into the casing of the electrophoresis apparatus rather than exist as a separate component. This not only ensures that the footprint of the apparatus is acceptable in terms of the laboratory bench space it occupies but also means that the researcher or the like running gels on the equipment does not have to worry about wiring multiple power supplies as the equipment is encapsulated in one apparatus.

The present invention also provides the ability for the computer control means to collect power supply/consumption data and to graph operating parameters of each output/cell in real time. This allows the person running the experiment to store electrophoresis run data for each gel.

A further feature of the present invention is that a single computer control means may be used to control all six output channels.

A particular advantage of the present invention is that having all the wiring built into the instrument, safety issues relating to the use of the apparatus close to a wet environment are minimised.

Although the specific embodiment described above provides six individually controllable outputs, it will be appreciated that greater or fewer output channels could be provided.

Further, although the switch mode transformer has 200 turns on its primary and secondary windings, it will be appreciated by the person skilled in

the art that the number of turns may be varied. For example 400 turns could be provided on the secondary to double the output voltage from 200V to 400V.

Also, by a simple modification of the secondary circuit, specifically by the addition of a voltage multiplier, higher voltages (over 1kV) can be provided for techniques that may require higher voltages such as iso-electric focussing or multi-compartment electrolysis.

It will be appreciated by the person skilled in the art that apart from electrophoresis, the multi-channel power supply of the present invention may be used in other applications where an electric field is applied to a biological sample such as electro-blotting, and electroporation specialised forms or electrophoresis or separation of biomolecules or other organic or inorganic molecules.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.