GB2414872A

GB2414872A - Flashlamp drive circuit

Info

Publication number: GB2414872A
Application number: GB0412352A
Authority: GB
Inventors: Michael Noel Kiernan; Jan Simonsen
Original assignee: Cyden Ltd
Current assignee: Cyden Ltd
Priority date: 2004-06-03
Filing date: 2004-06-03
Publication date: 2005-12-07
Anticipated expiration: 2024-06-03
Also published as: EP1754396A1; GB0412352D0; TW200610446A; US7710044B2; WO2005120137A1; GB2414872B; US20080067946A1

Abstract

A flash lamp drive circuit including a storage capacitor which is charged and selectively discharged in order to drive a flashlamp. A capacitor (116) is connected in parallel with each respective flashlamp (106) in a bank of flashlamps. Each capacitor (116) has a comparatively small capacitance so as to be capable of storing only a portion of the total energy pulse required to be delivered to the respective flashlamp (106). A controller, comprising a digital signal processor (118) and a microprocessor (120) is provided to control the operation of all of the flashlamps (106) in the bank via respective switch mechanisms (110). In use, each energy (or drive) pulse delivered to a flashlamp (106) is comprised of a plurality of smaller energy packets resulting from repeated charging and discharging of the respective capacitor (116). Thus, the shape and duration of the current pulses delivered to the flashlamp (106) is highly controllable and the size of the storage capacitor (116) required is significantly reduced relative to the prior art.

Description

24 1 4872 Flashlamp Drive Circuit This invention relates generally to a

drive circuit for a pulsed radiation source and, more particularly (but not necessarily exclusively), to a flashlamp drive circuit including a storage capacitor which is selectively discharged in order to drive a flashlamp.

Pulsed tlashlamps are used h1 a variety of applications, hlcludirlg optical cosmetology and dermatology applications. Such lamps normally operate at a comparatively high peak voltage, current and light h1tcnsity/po\vcr. In order to achieve such high values, power supplies or drives for such lamps typically employ a storage capacitor, which is charged between flashes or pulses, in series with an inductor and some kind of switch.

Thus, referring to Figure 1A of the drawings, there is illustrated a simplified version of a conventional flashlamp drive circuit, in which a power supply unit 100 is used to charge a relatively small capacitor 102, in this case say 5001lF. A switch 104 is provided between the capacitor 1()2 and tile flashlamp 1()6. Examples of switches used in the past have included thyristors, which once turned on, generally remain on until the capacitor has fully discharged, and transistors. When the switch 104 is closed, the capacitor 102 is substantially completely discharged to the flashlamp 106, giving a drive current pulse similar to that illustrated in Figure IB, whereby around (say) I 50J of energy (defined by the area under the curve in Figure I B) is delivered to the flashlamp in around 5ms.

However, there are applications, particularly medical applications, where the shape of the optical pulses used to drive the flashlamp is important in order to achieve the desired therapeutic effect, and in particular to achieve such effect without damage to areas of the patient's body not being treated. For- example, in optical dcnnatology, it may be desirable to rapidly heat a target chromophore to a selected temperature, and to then reduce applied energy so as to maintain the chromophore at the desired temperature. It is therefore highly desirable for the shape and duration of the optical pulses delivered to the flashlamp to be controllable.

Referring to Figure 2A of the drawings, there is illustrated a simplified form of another known flashlamp drive circuit, in \vhich a power supply UTlit 1(30 is-used to charge a relatively large capacitor 102 (say' 0.2F) up to, say ISOOJ, and a switch 104 (embodied in this case by a transistor) is used to deliver a small portion of this total energy (say I SOJ) at a time. In view of the manner ot' operation of' this type of partial discharge system, an optical pulse can be delivered to the flashlamp 1()6 with a relatively uniform energy distribution, as illustrated in Figure 213 of' the drawings.

ISffectively, a drive system of the type illustrated in Figure 2A of the drawings, delivers a plurality of small packets 108 ol' energy. Thus, in the case where ISOJ of energy are delivered in a SOms time interval, each packet 108 will consist of 0.03J/s.

As a result, it is possible, using such a system, to control the shape of the optical pulse delivered to the flashlamp in order to achieve the desired et'f'ect.

However, a major disadvantage of the partial discharge system described with reference to Figure 2A of the drawings, is the size ol' the capacitor 102, whereas it is highly desirable in all flashlamp applications to miimise the size of the capacitor (and therefore the charge it carries) as this has the effect of minimising the size, weight and cost of the lamp drive circuitry and enhances the safety of such drive circuits by reducing shock risks.

It is an object of the present invention to provide flashlamp drive circuitry, and a corresponding method of driving a ilashlamp, whereby the shape and duration of the eurTent pulses delivered to the flashlamp is highly controllable, and the size of the storage capacitor required is significantly reduced relative to known arrangements.

In accordance with the present invention, there is provided a pulsed radiation source drive circuit for delivering an energy pulse to a radiation source, said circuit comprising a storage Capacitor having a comparatively small capacitance so as to be capable of storing only a portion of the total energy oi'the energy pulse required to be delivered to said radiation source, said circuit l'urther comprising means for selectively charging and discharging said storage capacitor at a comparatively high frequency so as to deliver to said radiation source said energy pulse in the form of a plurality of packets of energy within a predetermined time period.

Thus, the present invention is intended to provide a drive circuit, preferably for a flashlamp, which drive circuit effectively mimics the operation of the partial discharge system described above witlJ rel'erence to Figure 2A of the drawings, using a relatively very small capacitor by proviling means for performing relatively high frequency charging and discharging of tle capacitor, i.e. the capacitor output is modulated at a high Frequency to aclievc the desired energy pulse.

Also in accordance with the present invention, there is provided a method of driving a pulsed radiation source, the method comprising providing a storage capacitor having a comparatively small capacitance so as to be capable of storing only a portion of the total energy of an energy pulse rcqtrired to be delivered to said radiation source, and selectively charging and discharging said storage capacitor at a comparatively high frequency so as to deliver to said radiation source said energy pulse in the form of a plurality of packets of energy within a predetermined time period.

The present invention extends lo a flasllamp unit comprising a flashlamp and including a drive circuit as defined above for driving said flashlamp.

The present invention extends still further to a digital signal processor for use in a drive circuit as defined above, tle digital signal processor being arranged and configured to control the operation of switch means so as to selectively charge and discharge said storage capacitor at a comparatively high frequency so as to deliver to said radiation source an energy pulse in the dorm of a plurality of packets of energy within a predetermined time period.

Preferably, the pulsed radiation source comprises a flashlamp.

Beneficially, the means for selectively charging and discharging the capacitor comprises switch means, and drive means for selectively opening and closing said switch. The switch may, for example, comprise an insulated-gate transistor, such as an insulated-gate bipolar transistor (IGBT).

In a preferred embodiment, the storage capacitor is connected in parallel with the pulsed radiation source.

A flashlamp unit according to the invention may comprise a plurality of flashlamps, each having associated therewith a respective storage capacitor and respective means for selectively charging and disclarghg said storage capacitor. Means, such as a digital signal processor and microprocessor, are heneticially provided for controlling the plurality of means lor selectively charging and discharging the respective storage capacitors.

These and other aspects of the present invention will be apparent from, and elucidated with reference to the embodiment described herein.

An embodiment of the present ins cation will now be described by way of example only and with reference to the accoupanyLlg drawings, in which: Figure 1A is a simplified circuit diagram of a first flashlamp drive circuit and flashlamp configuration according to the prior art; Figure IB illustrates an energy pope which can be delivered by the circuit of Figure 1A; Figure 2A is a simplified circuit diagram of a second {lashlamp drive circuit and flashlamp configuration according to the prior art; Figure 2B illustrates an energy pulse whirls can be delivered by the circuit of Figure 2A; Figure 3 is a schematic circuit diagram illustrating a tlashlamp drive circuit and flashlamp configuration according to an exemplary embodiment of the present invention; Figure 4 illustrates schematically a portion of the circuit of Figure 3; and Figures 5A and 5B illustrate energy pulse l'orms which can be delivered by the circuit of Figure 3.

Referring to Figures 3 and 4 of talc drawings, there is illustrated a tlashlamp unit including a drive circuit according to act exemplary embodiment of the present invention. The ilashlamp 106 may, l'or example, comprise a delivery head carrying light emitting apparatus in the for m of' act electric discharge tube containing a high pressure Noble/inert gas such as Xenon or Krypton. The discharge tube operates to produce, in response to the input of a current pulse, a burst of light of a range of wavelengtl1s in the visible spectrum (approximately in the range 400 to 700 nary).

However, many different types oi'tlashlamps and other pulsed radiation sources will be well known to a person skilled in the art, and their specific form and structure will not be described in any further detail herein. A bank of', say, six flashlamps or other pulsed radiation sources may be pi ovided in a single unit, as required by the particular application.

Associated with the or each flashlanp 106, there is provided a switch mechanism 110 comprised of an insulated-gate bipolar transistor (IGBT) 112 and a corresponding driver 114. The switch mechanism 110 also incorporates a secondary transistor 116, having a comparatively very small capacitance of (say) loaf. The capacitor l 16 and the respective flashlamp 106 are connected in parallel with each other. A controller, comprising a digital signal processor (DSP) 118 and a microprocessor 1 20, is provided to control the operation of all of the ilashlamps 106 in the bank via the respective switch mechanisms 11(). it will be appreciated that the microprocessor can be programmed so as to cause the digital signal processor to run the bank of flashlamps in accordance with any one ot'a number of different programs, depending on the application.

A switch mode power supply 122 and a pr imary capacitor 124 are also provided.

In use, each drive pulse delivered to a ilashlamp 106 is comprised of a plurality of smaller energy packets resulting from the high frequency, repeated charging and discharging of the respective capacitor 116, controlled by the DSP 118 via the respective driver 114. As a result, there is provided flashlamp drive circuitry, and a corresponding method of driving a llashlanp, whereby the shape and duration of the current pulses delivered to the flasllamp is highly controllable, and the size ol' the storage capacitor required is significantly reduced relative to known arrangements.

Examples of the types of energy pulses which can be delivered using the drive circuit described above with reference to l;igure.i 3 and 4 of the drawings, arc illustrated in Figure 5 of the drawings.

It should be noted that the above-nicntioned embodiments illustrate rather than limit the invention, and that those skilled in the art will he capable of designing many alterT1ativc embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the clain1s. 'the word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference ol' such elements and vice-versa. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS: 1. A pulsed radiation source drive circuit for delivering an

energy pulse to a radiation source, said circuit comprising a storage capacitor having a comparatively small capacitance so as to be capable of storing only a portion of the tote] energy of the energy pulse required to be delivered to said radiation source, said circuit further comprising means for selectively charging and discharging said storage capacitor at a comparatively high lrequcocy so as to deliver to said radiation source said energy pulse in the form of a plurality of packets of energy within a predetermined time period.
2. A circuit according to claim 1, wherein said pulsed radiation source comprises a flashlamp.
3. A circuit according to claim I or claim 2, wherein said means for selectively charging and discharging the capacitor comprises switch means, and drive means for selectively opening and closing said switch means.
4. A circuit according to any one of claims I to 3, wherein said storage capacitor is connected in parallel with the pulsed radiation source.
5. A method of driving a pulsed radiation source, the method comprising providing a storage capacitor having a comparatively small capacitance so as to be capable of storing only a portion of the total energy of an energy pulse required to be delivered to said radiation source, and selectively charging and discharging said storage capacitor at a comparatively high frequency so as to deliver to said radiation source said energy pulse in the form ol a plurality of packets of energy within a predetermined time period.
6. A llashlamp unit comprising a flashlamp and including a drive circuit according to any one of claims I to 4 for driving said flashlamp.
7. A flashlamp unit according to claim 6, comprising a plurality of flashlamps, each having associated therewith a respective storage capacitor and respective means for selectively charging and discharging said storage capacitor.
8. A flashlamp unit according to claim 7, wherein means are provided for controlling said plurality of means for selectively charging and discharging the respective storage capacitors.
9. A digital signal processor for use in a drive circuit according to any one of claims I to 4, said digital signal processor being arranged and configured to control the operation of switch means so as to selectively charge and discharge said storage capacitor at a comparatively high frequency so as to deliver to said radiation source an energy pulse in the form of a plurality of packets of energy within a predetermined time period.
10. A digital signal processor according to claim 9, being arranged and configured to control the operation of a plurality of switch means.