Unlocking Ultimate Safety: AC/DC and DC/DC Converters Revolutionize Endoscope Technology

Navigating the intricacies of endoscopic technology presents formidable challenges. As invasive instruments, endoscopes must comply with stringent leakage current requirements while fulfilling diverse power needs, from illuminating lights to powering motors and cameras. Addressing these complexities,
P-DUKE offers a comprehensive array of DC/DC products tailored to meet CF requirements, ensuring leakage currents remain below 10µA.

The electrical safety of medical devices is essentially ensured by two protective measures:

1. Isolation barriers between high and dangerous AC or DC voltages and low supply voltages for electronic equipment connected to the patient. This topic is covered in our patient monitor case study.
2. Leakage currents potentially flowing through the patient’s body are limited. While leakage currents of up to 30mA are permitted in industrial and domestic applications, the limits in medical applications are significantly lower. Medical standards define 3 categories:

Type B (body) – applied part with no patient connection
Type BF (body floating) – applied part with patient connection
Type CF (cardiac floating) – applied part with patient connection and suitable for cardiac use

Under normal operating conditions, the leakage currents must not exceed the following limits:

The main source of leakage currents is EMI filters used on the primary side of AC/DC power supplies. P-DUKE has many AC/DC power supplies with built-in EMI Class B filters meeting the 100µA leakage current requirements for Type BF applications (patient contact) (see figure 1). However, meeting the 10µA limit for CF applications with AC/DC power supplies alone would require extremely large EMI filters.

Figure 1: potential applications for AC/DC and DC/DC converters.

Therefore a combination of AC/DC power supplies with downstream CF compliant DC/DC converters is used. Let’s look at a practical example.

Today, medical endoscopes are not only used for diagnostics but also for micro-invasive operations and incorporate modern optics, motor and software technologies and high-precision mechanics. These devices are used inside the human body and can get close to the heart and in contact with the bloodstream. Therefore they must meet the 10µA leakage current limits of CF type applications.

This customer wanted to design a smaller video endoscope with an LED light source, a camera built into the endoscope head and the movement of the head controlled by small motors.

How does P-DUKE's comprehensive range of power solutions facilitate the creation of an efficient power solution for medical endoscopes?

The systems consist of a central processing unit with a microprocessor, interfaces to the external video processing unit, the hospital information system and an optional external storage device. Total power consumption is around 26W.

The endoscope needs 5V/20W for the LEDs and the camera and a 12V/5W supply for small motors moving the head via Bowden cables.

The total power consumption of the system is in the range of 44W. With the comprehensive set of converters from P-DUKE it was easy to create a very flexible solution (see figure 2).

Figure 2: Block diagram endoscope power solution

From AC mains a 65W MAD65 medical AC/DC power supply generates a 12V bus voltage. It is a plug-and-play solution as it has a built-in EMI Class B filter and meets the medical requirements for 4000Vac reinforced isolation and 2xMOPP.

P-DUKE has a very comprehensive set of AC/DC power supplies ranging from 15W up to 450W. All products are 2xMOPP compliant and have been updated to the latest medical safety approval EN60601-1 ED3.2

The various supply voltages for the electronics were generated by downstream medical DC/DC converters from P-DUKE. With leakage currents far below the 10µA limit, they all are CF compliant.

For the microprocessor, a 5V/20W module is used and an additional 5/10W converter isolates all interfaces from the internal systems.

The same 5V/20W module as for the microprocessor is used to supply LEDs and cameras of the endoscope and a 12V/5W converter drives the motors. If a 3.3V supply is needed, it can easily be generated with a small additional converter.

The comprehensive set of medical converters from P-DUKE made it easy to design a very flexible solution meeting all the necessary safety requirements.

For a redesign, the customer is considering replacing the MAD65 AC/DC power supply with the new MAD50 50W series.
It’s footprint (3” x 1.5”) is 25% smaller than the MAD65 (3” x 2”) freeing up space for additional features.