GB2349283A

GB2349283A - Isolated power supply for a peripheral device coupled to a computer

Info

Publication number: GB2349283A
Application number: GB9908749A
Authority: GB
Inventors: Hugh A Thomas
Original assignee: DATA ACQUISITION SYSTEMS Ltd
Current assignee: DATA ACQUISITION SYSTEMS Ltd
Priority date: 1999-04-17
Filing date: 1999-04-17
Publication date: 2000-10-25
Also published as: GB9908749D0

Abstract

A power supply coupled between a data port of a computer and a peripheral device 1 converts data signals received from the computer into an electrical power signal and transfers power from the power signal to the peripheral device across an electrical isolation barrier T1. The peripheral device may be a physiological monitoring device (eg. for EEG or ECG signals) and the data port may be an RS-232 port which does not have dedicated power supply lines. Diodes D1, D2, D3 and capacitors C1, C2 are connected to the DTR, RTS and TXD lines of the port to derive positive and negative supply voltages for a switch mode converter 14 which powers the peripheral device via an isolating transformer T1. The switch mode converter may have a soft start feature (Fig. 3). Data and control signals are exchanged between the port and the peripheral device via opto-isolators. A USB or IEEE 1394 port may be utilised (Fig.4) instead of an RS-232 port.

Description

ISOLATED POWER SOURCES The present invention relates to isolated power sources and more particularly, though not necessarily, to isolated power sources for supplying power to physiological measurement devices and instruments.

A large and varied range of medical recording equipment is available to medical practitioners to assist in the monitoring, diagnosis, and treatment of patients. For example, equipment is available for recording heart rate, electrocardiograms (ECGs), electroencephalograms (EEGs), and blood pressure. As such equipment is extremely specialised, and the demand is small relative to the demand for consumer products, the equipment tends to be expensive. Indeed, high cost tends to be a feature common to much medical equipment including that used for diagnosis and treatment.

The high cost of medical equipment is often due at least in part to the need to electrically isolate instruments intended to be placed into contact with parts of the human body both to protect patients from dangerous power spikes and surges and to protect the instruments themselves from potential sources of interference.

It is an object of the present invention to provide an isolated power source for powering peripheral devices and which is relatively low in cost. It is a further object of the present invention to provide an isolated power source which facilitates the connection of peripheral devices to computers or other standard electronic equipment to exchange digital data therewith and to provide power for the peripheral devices.

These and other objects are achieved at least in part by providing an isolated power source arranged to be coupled to the serial port of a computer or computer device, and which can convert digital data signals received from the computer or computer device into power for supplying to a peripheral device across an isolation barrier.

According to a first aspect of the present invention there is provided a power source for coupling between an input/output data port of a computer and a peripheral device, the power source comprising : a data port arranged in use to be connected to said computer port to receive digital data signals therefrom; output means for coupling to said peripheral device to provide electrical power to the peripheral device; conversion means for converting at least a part of the data signals received from the computer port at said power source data port into an electrical power signal; and isolation means including an isolation barrier, coupled between said conversion means and said output means for transferring power from said power signal from the conversion means to the output means across the isolation barrier.

The power source according to the present invention enables specialised peripheral devices to be coupled to standard input/output data ports of computers. As a result, the need for additional specialised interface and/or control and recording apparatus is obviated or eliminated. Moreover, the provision of power and the transfer and processing of digital data may be handled by a single standard computer.

It will be appreciated that the term"computer"as used here refers to personal computers and workstations as well as to other electronic equipment utilising computer processors.

Preferably, the conversion means of the power source comprises an inverter. More preferably, the inverter is a switched mode power supply.

Preferably, the isolation barrier of the isolation means is a transformer. Alternatively, the isolation barrier may comprise a capacitor.

Preferably, said data port of the power source is a serial port and is arranged to be coupled to a serial port of a computer. More preferably, these serial ports are RS-232 ports. Alternatively however, the data port of the power source is a USB port arranged to be coupled to a corresponding USB port of a computer.

According to a second aspect of the present invention there is provided an interface unit comprising a power source according to the above first aspect of the invention, the unit comprising means for transferring digital data signals received from the computer at said data port to the peripheral device. Data signals may be transferred across said isolation barrier or via a second output means of the interface unit.

Preferably, the interface unit comprises means for receiving data signals from a peripheral device. These signals may be analogue or digital. More preferably the unit comprises means for coupling the received data signals to the said data port of the power source for transmission to the computer data port (after analogue to digital conversion if necessary).

In certain embodiments of the present invention, the interface unit comprises active and/or passive electrical circuits for processing digital data received from the computer or the peripheral device. For example, the unit may comprise an amplifier for amplifying signals received from a peripheral device and/or an analogue to digital converter for converting analogue signals received from a peripheral device into digital signals for transmission to a computer. The interface unit may also comprise for example filters and microprocessors.

According to a third aspect of the present invention there is provided apparatus for monitoring physiological parameters from a patient, the apparatus comprising: monitoring means for attachment to a patient and arranged in use to generate electrical signals corresponding to monitored physiological parameters; a power source having a data port arranged in use to be connected to a data port of a computer to receive digital data signals therefrom, output means coupled to said monitoring means to provide electrical power to the monitoring means, conversion means for converting at least a part of the digital data signals received from the computer port at the power source data port into an electrical power signal, and isolation means including an isolation barrier, coupled between said conversion means and said output means for transferring power from said power signal, from the conversion means to the output means across the isolation barrier.

According to a fourth aspect of the present invention there is provided a method of coupling power and digital data signals between a peripheral device and a computer having an input/output data port, the method comprising the steps of : receiving digital data signals from the computer data port; converting said received digital data signals into a power signal; transferring power from said power signal across an isolation boundary; and providing said transferred power to a peripheral device.

For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which: Figure I illustrates in block diagram form an isolated low power source coupled between a personal computer and a peripheral monitoring device; Figure 2 illustrates the isolated low power source of the arrangement of Figure 1 ; Figure 3 illustrates a modification to the isolated low power source of Figure 2; and Figure 4 illustrates an alternative isolated low power source utilising a USB port of a computer.

With reference to the block diagram of Figure 1, there is illustrated a peripheral device 1 which requires a DC power voltage 2 for its operation. When powered, the peripheral device I generates digital signals 3 depending upon its purpose. The peripheral device I may be an instrument arranged to detect some physiological parameter from a monitored patient. More particularly, such physiological data may be an EEG or an ECG signal. Where the peripheral device 1 is designed to monitor physiological data, the device I will typically comprise some appropriate sensor means such as one or more electrodes.

In order to protect the peripheral device 1, or a patient or instrument connected to the device, the device 1 is isolated from the power supply from which the DC power 2 is derived. In Figure 1, the peripheral device 1 is shown connected to a low power isolated source 4 which is in turn coupled to a personal computer 5. Digital data signals 6 are coupled between the power source 4 and the computer 5 via an RS-232 connection comprising RS-232 ports 7,8 provided at the personal computer 5 and at the power source 4, and an RS-232 connecting cable (not shown). Digital data 6 transferred via the RS-232 connection may include measurement signals 9 being transferred from the peripheral device 1 to the computer 5, and control data 10 being transferred from the computer 5 to the peripheral device 1.

The skilled person will appreciate that serial ports such as RS-232 ports are not normally intended to facilitate the transfer of power signals. More particularly, the RS-232 standard does not allocate pins or lines for the provision of a DC power signal. Under normal circumstances therefore, the power signal required by the peripheral device 1 would be provided via a separate power source connected for example to mains power or to a battery. However, as is illustrated in detail in Figure 2, the low power source 1 proposed here derives a DC power supply signal from the digital data signals 6 sent from the computer 5 over the RS232 connection.

Figure 2 illustrates in more detail the power source 4 of Figure 1. The power source 4 has a switched mode power supply 11 having inputs V+ and V-coupled to certain pins of the RS-232 port 6 of the isolated power source 4. More particularly, RS-232 pins DTR and RTS are coupled to the input V+ via respective diodes D I and D2, whilst RS-232 pin TXD is coupled to the input V-via diode D3. The V+ input of the switched mode power supply is coupled to ground pin SGND via capacitor Cl whilst the V-input is coupled to pin SGND via a capacitor C2. The output of the switched mode power supply is coupled to the input winding 12 of an isolation transformer TI, whilst output winding 13 of the transformer Tl is coupled to DC power supply output pins +ve and-ve of the power source via a rectifying diode D4. A smoothing capacitor C4 is connected across the DC outputs-ve and-ve.

The DC outputs +ve and-ve of the transformer Tl are coupled to the power inputs of the peripheral device 1. Actual data signals 3 are coupled to and from the peripheral device 1 via a pair of optical isolators 16, which ensures isolation of the data signals.

The operation of the isolated power source of Figure 2 will be readily apparent to the skilled person. More particularly, it will be appreciated that the power source 4 is able to convert digital signals provided at the RS-232 port 6 of the source 4 into a DC supply at the DC output pins +ve and-ve. The isolated nature of the source will also be apparent to the skilled person.

Figure 3 illustrates a modification to the isolated power source of Figure I and which is designed to provide a"soft start"mode. In this example, the switched mode power supply 14 is provided by a Maxim Max 634TM integrated circuit. The output voltage of the switched mode power supply 14 is rectified by a diode D5 and smoothed by a smoothing capacitor C5 to provide a DC voltage which is fed back for comparison with a reference voltage in order to regulate the output of the supply 14. If the voltage across the capacitor Cl is less than the voltage drop across a zener diode D6 (as occurs for example during the power-up period), then a diode D7 is forward biased by a pull-down resistor R1, resulting in the switched mode power supply 14 reducing its load current on the capacitor Cl, thus providing a low current soft start.

Figure 4 illustrates an alternative embodiment of the present invention which is similar in principle to that of Figure 2, but in which the isolated power source 4 comprises a USB or an IEEE 1394 interface port 15 for coupling to a USB or IEEE1394 interface port of a personal computer. There is a trend in the computer industry to provide in particular USB ports as standard on computers and computer devices and the embodiment of Figure 4 aims to provide compatibility for future computers.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention.

Claims

Claims 1. A power source for coupling between an input/output data port of a computer and a peripheral device, the power source comprising: a data port arranged in use to be connected to said computer port to receive digital data signals therefrom; output means for coupling to said peripheral device to provide electrical power to the peripheral device; conversion means for converting at least a part of the data signals received from the computer port at said power source data port into an electrical power signal; and isolation means including an isolation barrier, coupled between said conversion means and said output means for transferring power from said power signal from the conversion means to the output means across the isolation barrier.
2. A power source according to claim 1, wherein the conversion means of the power source comprises a switched mode power supply.
3. A power source according to claim 1 or 2, wherein the isolation barrier of the isolation means is a transformer.
4. A power source according to any one of the preceding claims, wherein said data port of the power source is a serial port and is arranged to be coupled to a serial port of a computer.
5. A power source according to claim 4, wherein the serial port of the power source is an RS-232 port.
6. A power source according to any one of claims I to 3, wherein the data port of the power source is a USB or IEEE 1394 port.
7. An interface unit comprising a power source according to any one of the preceding claims, the unit comprising means for transferring digital data signals received from the computer at said data port to the peripheral device.
8. An interface device comprising a power source according to any one according to any one of the preceding claims, or according to claim 7, and comprising means for receiving data signals from a peripheral device and for coupling the received data signals to said data port of the power source for transmission to the computer data port.
9. Apparatus for monitoring physiological parameters from a patient, the apparatus comprising : monitoring means for attachment to a patient and arranged in use to generate electrical signals corresponding to monitored physiological parameters; and a power source having a data port arranged in use to be connected to a data port of a computer to receive digital data signals therefrom, output means coupled to said monitoring means to provide electrical power to the monitoring means, conversion means for converting at least a part of the digital data signals received from the computer port at the power source data port into an electrical power signal, and isolation means including an isolation barrier, coupled between said conversion means and said output means for transferring power from said power signal, from the conversion means to the output means across the isolation barrier.
10. A method of coupling power and digital data signals between a peripheral device and a computer having an input/output data port, the method comprising the steps of : receiving digital data signals from the computer data port ; converting said received digital data signals into a power signal; transferring power from said power signal across an isolation boundary; and providing said transferred power to a peripheral device.