Innovations in Laser Power Solutions for Medical Applications

­According to a report by Straits Research, the market for aesthetic lasers and energy devices was valued at USD 4.46 billion in 2021, with a projection that it will exceed USD 10 billion by 2030 – a growth of over 10% PA.

Developments in the laser technology have created new laser-based treatments such as resurfacing and rejuvenating vascular lesions. Laser treatments are not just aesthetic, though, as they are used for medical procedures in areas such as oncology, cardiology, ophthalmology and gynecology to avoid the need for invasive surgery. In many cases, this also results in patients receiving treatment more quickly and conveniently, with minimal recovery times.

While the equipment in this sector shares one common attribute – reliance on a laser to deliver the benefit - there are several different types of systems in use. Surgical lasers tend to be large, fixed machines that are used for ophthalmic procedures and general surgical procedures. Multi-function machines are typically portable with the capability to perform several types of aesthetic treatments including laser, IPL, RF and thermal. The final type is ‘laser only’ – this is a specialized system with a high-power laser for a specific application, such as the removal of unwanted hair.

Medical Lasers and IPL Systems

There is a significant amount of change occurring in the medical laser arena. With the growing popularity of this type of treatment, there are many more multi-functional machines reaching the market. These are well suited to smaller clinics and mobile use as they allow a number of treatments to be offered from a single machine. As these systems are usually close to the patient (and operator) while being used, audible noise is coming under increased scrutiny – so active cooling measures such as fans are generally not preferred.

A typical multi-purpose aesthetic laser system will consist of several sub-systems other than the laser itself, including an HMI, pumps, control boards, thermal management and the medical applicators. As a result of this variety of system elements, often a relatively complex power solution is required to provide the various rails for each of the modules.

One common approach is to use a configurable power supply, with a large number of independent outputs powered by the appropriate output module for each rail. This approach is favored by designers as two different systems with disparate components can use the same configurable chassis across an entire product range, simplifying design. Additionally, if a customer wishes to upgrade existing equipment, a configurable supply can be modified in the field.

There is a separate requirement for a capacitor charger in these systems, to charge the capacitors that provide bursts of energy for the IPL and laser. As this is not part of the configurable supply, a separate unit has traditionally been used.

While this dual module approach works, it does provide designers with a number of challenges. Firstly, as there are two separate mains-driven power supplies (PSUs), there are two sources of leakage current – as well as two safety critical components. Additionally, each PSU produces its own radiated and conducted RFI which can combine, causing design challenges and making compliance with ever-more-stringent medical approvals more difficult.

Using a single module to charge the capacitors for both laser and IPL delivers sub-optimal performance. As the laser generally requires a higher charging voltage than IPL, and the capacitor chargers operate on constant current, then less power is delivered to the capacitors for IPL. While this does not impact the operation, it does extend the charging time which, in turn, means that any treatment procedure takes longer. Clearly, the faster a clinic can perform their treatments, the less a patient will be inconvenienced from a time perspective. Additionally, these time savings permit clinics to treat more patients

Ideal Power Solution for Multi-Purpose Laser Systems

Using a single PSU to supply all of the lower voltages for the sub-systems as well as charging the capacitors will reduce size and weight. It will also reduce leakage currents and the potential EMI problems and interactions that can be caused by using more than one mains PSU in the system. A beneficial approach would be similar to a configurable PSU whereby output modules are easily interchangeable; this allows for easy upgrading and repairs in the field, and also drives a high degree of commonality in a range of laser systems, simplifying the design process.

A single PSU approach would require constant voltage for the lower voltage rails with constant current for the capacitor charger. However, with the different voltage requirements for IPL and laser, this results in lower utilization of available power on all treatments.

Clearly, small size and low weight are desirable. This implies high efficiency as less waste heat is generated, meaning that the design can be more densely packed and fewer thermal management techniques are needed. Reliability is critical as, given the cost of the end system, many smaller clinics may only have one available and the impact of failure could be significant.

In the medical field, approvals are more important than in many other sectors. This is especially true where either the patient or the operator comes into direct contact with the equipment. From a safety perspective, the PSU will be the primary separation between dangerous mains voltages and the human operator / patient in the event of a fault. Therefore, proper medical safety approvals are required – and other approvals such as EMI are highly desirable to ensure proper operation.

PSU Technologies for Medical Lasers

While high voltage (HV) PSUs can be directly mains-driven, an alternate approach is to use a DC-DC module. This reduces space as there is no need for an isolation boundary within the module itself, relying instead on the medically approved isolation in the front-end PSU.

One such PSU is AE’s UltraVolt series of DC-DC precision high voltage amplifiers (HVAs) that use a precision filter / divider and linear HV switch to deliver a high-resolution, high voltage DC. The family includes unipolar and bipolar units offering 0 to 10 kV adjustable outputs as well as fixed 15 kV (bipolar only) and 20 kV. The modules are optimized for bias applications while providing PPM level line and load regulation, high dynamic response, and stability – including a temperature coefficient of 25 ppm. These products have been deployed in a number of medical applications including, most recently, a new femtosecond ocular laser surgery system. This system was developed to allow precise procedures to be carried out without collateral damage to other parts of the eye and required a fast-reversing 6 kV PSU that was also capable of controlling an external Pockels cell within the CO₂ laser. Tight control of the laser as well as exceptional reliability were required as any mid-procedure downtime would be disastrous.

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Figure 2: AE’s UltraVolt series met the challenging needs for femtosecond ocular laser surgery

An UltraVolt 6HVA24-P1 was selected for this application, powering the system’s external energy modulator and satisfying all the requirements.

Integrated Power and Capacitor Charging Solution

AE’s new Excelsys FlexiCharge FC1500 is specifically aimed at addressing the somewhat complex needs of laser / IPL systems. It incorporates a capacitor charger with a modular / configurable 800 W auxiliary power solution that share a common front end, thereby removing issues such as double leakage current and EMI interactions. Not only does this save around 30% of the space required by a traditional two-unit solution, it also significantly simplifies safety approvals as there is now only one critical component – the FlexiCharge PSU that carries the required safety approvals (IEC60601-1 3^rd Ed. And IEC60601-1-2 4^th Ed. (EMC).

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Figure 3: AE’s FlexiCharge provides a unique all-in-one solution for low voltage power and capacitor charging

A programmable power limit means the unit to take full advantage of the maximum available wall current, while PMBus intelligent control allows key operating parameters to be set just once and monitored forever, thereby simplifying configuration and operation.

The current control system is able to operate into large capacitances (>6,000 µF) as well as lower capacitance (>180 µF) loads. Pulse-to-pulse repeatability is excellent (±0.2%) and the supply can operate continuously at any voltage >200 V.

However, the most significant innovation is the introduction of constant power control, replacing the constant current control of other similar units. In constant current capacitor chargers, as IPL requires lower voltage it receives less power, meaning that the charging time is not as fast as it could be.

The FlexiCharge unit incorporates accurate constant power control through adaptive control being applied to every pulse. This important innovation ensures that the maximum available power is also available for the IPL, and charging times for IPL can now be faster than those for those for charging to the higher voltages required for the laser.

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Figure 4: Constant power control is a significant innovation with a real benefit in treatment times

Additionally, a current sense signal is provided to allow stress on the system capacitors to be monitored. It also allows power to be calculated so that MCBs within the system can be sized correctly – both of which enhance system reliability.

Advanced Energy