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Performance Factors and Design Flexibility In Medical Power Supplies

When dealing with medical equipment, strict standards are often put into place to make sure patients and healthcare personnel remain safe. However, beyond these strictly-enforced safety standards, it’s also worth considering how different power supplies stack up when it comes to performance. Here’s a look at some performance factors to help you pick the safest, most reliable power supply possible.

  • Standby power. Since hospitals, healthcare facilities and patients have become more concerned with energy efficiency and conserving resources, the amount of standby power consumed by devices is increasingly more important. Some medical power supplies use standby power as low as 0.15 watts, while similarly-sized devices consume up to 0.48 watts.
  • Environmental factors. Many DC-DC converters are limited to operating between ambient temperatures of -40 and 60°C at full load. Be sure to read specifications carefully, or ask your potential supplier about these engineering values to make the best decision. Aside from temperature constraints, two other factors worth considering are operating altitude and product warranties.
  • Electromagnetic interference (EMI). Medical devices like patient monitors, which operate with low-level signals in hospital settings, are more sensitive to EMI than typical industrial equipment. Whenever possible, look for medical power supplies with built-in EMI filters.
  • Packaging style. While the majority of power converters come with an open frame package, there are some other options available including chassis mount, DIN rail mount and enclosed configurations. Depending on the medical equipment, power supply packaging can play a key role in overall design.
  • Overall performance. When possible, look for power supplies that offer additional design flexibility. For instance, having a wider input range translates to greater flexibility for unforeseen design iterations requiring higher input voltages, or the need to develop several versions of the same basic equipment.  

Efficient, Low Noise DC-DC Converters Save Space

It’s not often you come across a power supply with both ultra low noise and high efficiency—you usually have to trade off one for the other. With our new TLB5 series of DC-DC converters, you get both, along with many other compelling features. Let’s take a closer look.

Low noise, high efficiency. At Polytron, we’ve designed and tested the TLB5 series for extra low noise. These DC-DC converters have an output ripple and noise of just 10 millivolts, thanks to a built-in EN55022 Class B filter for reducing electromagnetic interference.

In addition to the low noise, our TLB5 power supplies are highly efficient. While other models have efficiency rates in the low 80 percent range, this series tops out at 89 percent efficiency.

Space-efficient too. There’s another aspect of efficiency worth noting: the TLB5 ser ies saves space in your device. In many 2.5-watt single output applications, it’s common practice to double up a 2.5-watt power supply to meet the power requirements. With our 5-watt series, you can meet the same requirements with one small, compact DIP package of 1.25 x 0.80 x 0.40 inches.

Additional features. The TLB5 series has a wide operating temperature range up to 85°C and an input to output isolation voltage of 1600 volts. Other features include over current, short circuit, under voltage and over voltage protection, and a 4:1 wide input voltage range. This series also meets UL60950-1, EN60950-1 and IEC60950-1 safety standards. Some common applications include:

  • Telecommunications.
  • Data communications.
  • Measurement equipment.
  • Wireless network equipment.
  • Industrial control systems.
  • Semiconductor equipment.

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Easy-To-Follow International Wiring Instructions For Your Power Supply

To help reduce the likelihood of failure in your power supply, we’ve released a set of new pinout diagrams on our website with easy-to-follow global wiring instructions to simplify connecting your power supply.

These diagrams will help you install single, dual or triple output chassis mounts, as well as single, dual and triple output PC mounts. When installing your power supply, follow the proper instructions based on your input voltage and mounting type. Other international input voltages and voltage combinations are also available upon request.

One of the easiest ways you can avoid installation-related issues is by making sure your power supply has the right polarity so it retains sufficient power. If you accidentally reverse the polarity on the output side, you could damage your circuitry and the power supply.

 

Thermal Management For Power Supplies

To make sure your power supply runs efficiently for the long run, you need to remove heat from the device. Here are some ways that Polytron uses appropriate thermal management strategies to increase the mean time before failure (MTBF) and keep temperatures down in all our power supplies.

HWB100Potting Material. Using a thermally-conductive potting material helps dissipate heat while helping with shock and vibration. These potting materials feature a low thermal resistance and help carry heat away from the power supply electronics, improving cooling efficiency.

Forced Air Cooling. Forced air cooling speeds up heat dissipation to extend the life of our power supplies. In this method, a fan blows outside cool air across the top of the power supply. One of the biggest advantages of forced air cooling is that it requires little maintenance.

Heat Sinking. Internal heat sinking eliminates heat from inside power supplies by dispersing heat for improved efficient energy use. Bringing the heat sink to its outside surface allows for a more direct airflow to reach the direct source of heat. This method radiates heat so it doesn’t get trapped inside and over heat the power supply.

Conduction Cooling. Conduction cooling is sometimes used in our high wattage power supplies. This method mounts all internal heat sources to an isolated metal baseplate, which is then mounted to a heat sinking frame or housing.

 

How to diagnose power supply problems

QB150

Before leaving the plant, power supplies are always subject to performance testing. These tests include line regulation at full load and operating temperature.

The problem with these ideal testing conditions is that there's no guarantee that the operating conditions of a power supply will be consistent with the test conditions. One reason for this is that electrical components have performance tolerances – the most common being 5, 10 and 20 percent of the nominal value. This component tolerance effect is additive, which can keep the power supply from working properly.

Once you've ruled out tolerance issues, here is how you can diagnose a power supply problem.

No Load. Start by testing the power supply on a bench with no load. If it doesn't work, you'll know right away to contact the manufacturer for another unit. If the power supply works, you should test it with a resistive load to see if that's the problem.

Resistive Load. Failure with a resistive load can mean that your tolerances have caused a process or component failure. Other possible reasons for failure with a resistive load are if the component is out of specification or has a cold soldered joint. If the power supply still works with a resistive load, you'll want to test it with an active load.

Active Load. If the problem comes from the active load, it could be due to an unfamiliar signal caused by high capacitance. A large capacitor on initial power-up can act as a short circuit, forcing the unit into short circuit protection. At this point, you should check the manufacturer's specification to see if your unit has exceeded the maximum capacitive load.

If your power supply still doesn't work, you have two other options: either lower the capacitive load, or get a different unit with circuitry that can handle higher currents.