What are the misconceptions about selecting diodes in medical electronic devices?

一,Relying too much on fundamental electrical factors

When designing something, most engineers start by looking at the basic electrical specs of diodes, like reverse withstand voltage (VR), forward current (IF), and forward voltage drop (VF). These factors are the basis for deciding if the gadget is "usable," however for medical equipment, just achieving these standards is not enough.

Medical equipment must meet severe safety standards, such the IEC 60601 series specifications. These not only need electrical performance, but also set stricter standards for insulating level, leakage current

One concern is that engineers often employ generic diode models from consumer electronics or industrial devices without checking to see if they will work in medical settings. For instance, in circuits that have parts that touch patients

二,Don't worry about how reverse leakage current affects high-precision medical signals;

instead, do selection evaluation based on IEC 60601 early in the design process.

Most of the time, electrocardiogram (ECG) readings are in the millivolt or even microvolt range.

Electroencephalogram (EEG) signals are less strong.

Biosensors are very sensitive to noise.

In this case, the diode's reverse leakage current (IR) is an important factor. But people often forget about this parameter.

Schottky diodes and regular rectifier diodes may work fine at normal temperature, but when the temperature rises, the leakage current will rise very quickly, which will cause noise or offset to build up on the collected signal, making measurements less accurate.

Some common misunderstandings are:

Using regular diodes to make front-end protection circuits work

Not checking for leakage current in hot places

Don't pay attention to the changes in leakage current after the gadget has been used for a while.

Suggestions for improvement:

Use ultra-low leakage diodes in the signal link as a top priority.

Instead of general-purpose diodes, key nodes use special ESD protection devices.

Look closely at the IR vs. Temperature curve in the data handbook.

 

三,Misuse of Schottky diodes and ignoring their built-in problems

The key problems are:

The reverse leakage current is quite high and goes up a lot when the temperature rises.

The capacity to endure reverse voltage is usually minimal.

Not very good at keeping heat stable

In some cases, like precision detection circuits or low-noise systems, using Schottky diodes can cause mistakes that aren't needed.

Some common ways people misuse it are:

Using Schottky to defend against clamping in the front end of biological signal acquisition

Using cheap Schottky devices in equipment that works in high temperatures

Its long-term stability has not been confirmed.

Suggestions for optimisation:

A good use of Schottky in power rectification or DC-DC applications

Try not to use it in analogue and precision signal lines as much as you can.

Choose a low-leakage model if you need to and check the temperature.

 

四,Not giving enough thought to surge and ESD protection

But in real-world design, engineers often:

Use regular diodes instead of ESD protection devices.

Don't worry about designing interface level protection

Not doing ESD level verification according to the rules

Most diode don't respond quickly enough or clamp down hard enough to handle ESD shocks according to the IEC 61000-4-2 standard. This might cause serious damage to chips or problems with the system.

Suggestions for making things better:

To protect yourself, use special TVS (transient suppression) diodes.

Choose the right ESD level for the job, like ± 8kV or ± 15kV.

To lessen parasite impacts, put protection devices as close to the interface layout as you can.

五, Not thinking about long-term reliability, thermal design, or the stability of the supply chain

Long use cycle (5 to 10 years or more)

Long periods of continuous operation (24 hours a day, 7 days a week)

Very little room for mistakes

In this situation, the long-term dependability and stability of the supply chain for diodes have become very critical. But a lot of designs are still in the "as long as they can be used" stage.

Not thinking about how temperature affects how long a device lasts

Pick devices that are made for consumers instead of those that are made for industry or cars.

Ignoring how well packaging and PCB heat dissipation work in terms of heat transfer

Pick components from suppliers with limited lifecycles or that aren't well known.

The amount of leakage current goes up over time.

Parameter drift makes the system less accurate.

Stopping production late makes medical certification invalid.

Choose industrial or automotive-grade parts first.

Look into the thermal resistance (R θ JA) and find the best way to get rid of heat.

Pick a brand that has a Longevity Programme to get supplies for a long time.

Set up a BOM traceability system to fulfil the needs of medical audits.