Don Baldwin, Technical Support Manager for Power, Sager Electronics.
System designers often have to choose between standard, custom, and modular power supplies.
When designing a system that requires some form of power conversion, the power source (power supply or battery) is often one of the last items to be considered. In some ways this makes sense because the total power requirement for the system and the different voltages used within the system must be identified first before the power supply is selected. However, that may not leave enough time to properly choose the power supply that best meets all the needs of the system. Let’s look at some of the key considerations when choosing a power supply in the design of your end system.
The type of output current limit required to power the system load(s) affects the type of power supply that needs to be selected. A constant voltage output with a hiccup-mode over-current limit protection scheme is designed for a more resistive type of load, such as the controls or displays within a system. A hiccup-mode over-current limit will shut down the output once the over-current point is reached, and then turn back on after a short time to see if the load has fallen below the over-current point. If it has, the power supply will continue to provide power. If it has not, then the output will shut down again and repeat the cycle until the load is reduced, thereby causing the output to “hiccup.”
By comparison, a constant current output is designed to reduce the output voltage and maintain the output current until the output voltage reaches a low limit and the output is shut off. This type of over-current protection is designed for highly capacitive loads or battery charging.
Sager Electronics recently worked with a customer who required both a constant current output for charging batteries and a constant voltage output to power their system load. We identified the PBA series power supply from COSEL to power both output requirements—constant voltage or constant current. Working with Sager’s electrical and mechanical engineers to design a custom control board, a sheet metal enclosure, and DC/DC converters to regulate the battery voltage to the load, the customer was provided with a custom power solution using standard AC/DC and DC/DC power supplies.
Another consideration when designing your end system is its peak and steady state power requirements. Steady state refers to the power the system needs on a regular basis to perform its basic tasks, while peak refers to the power needed for a short period to perform a special task for the system. Driving a pump, a motor, a print head, or a highly capacitive load are examples of systems whose peak power needs may be substantially more than their steady state requirements. These items need extra power to begin moving or operating at start-up, after which they revert to require significantly less power to maintain their operation. If the power supply is designed to constantly meet the peak power requirements for the load, then you may be using a power supply larger than is necessary. Power supplies with peak/boost capability, or supplies that have both convection and air-cooled ratings, can be used to power these types of loads.
Rather than sizing the power supply for the worst-case peak current, a better option is to use a power supply that can provide the peak current while being designed for the non-peak operating power. For example, some power supplies are designed to meet peak power requirements two to three times their normal output ratings. In this case, the peak power rating will be specified with a maximum duty cycle and for a limited period. Calculations need to be made to ensure the power supply can meet the peak power requirements while maintaining an average power level below the steady state power capabilities of the power supply. If the peak power requirements are for a short enough duration with a reasonable duty cycle, the power supply can be designed for the lower steady state power requirements and still provide the power needed for the peak power requirements. This allows the system to use a smaller, less expensive power supply that still meets all the system power requirements. Sager stocks the leading manufacturers of peak power supplies such as Cincon, MEAN WELL, RECOM Power, TDK-Lambda, and others.
Another common design challenge is to decide between a single output supply in conjunction with multiple DC/DC converters vs. a custom power supply. Suppose your power supply needs to provide multiple output voltages to run all the different loads within your system. In that case, a single output supply with multiple DC/DC converters may not be the best solution due to space and complexity of the design. A custom power supply may be able to meet all your needs; however, such a device may have a long design cycle with high costs for non-recurring engineering (NRE) and agency approvals, and perhaps have minimum quantities that do not match your requirements. Even if a custom power supply does appear to offer the best choice, it may be that the system design is still in flux, the final output voltages and currents are not set in stone, but you still need power supplies to work out the final design, so what do you do?
One option is to consider a modular/configurable power supply. A modular power supply provides the ability to have up to 24 different outputs in a variety of sizes and power levels with low minimum quantities, no long design cycle, and no additional NRE charges or safety agency approvals. The modular power supply can be configured to provide the output voltages and currents your system needs to operate all of its different loads. Some of these outputs can even be configured for constant current operation or have peak power capabilities. The latest generation of modular products offers size, price, performance, features, and quality enhancements, making them attractive and reliable solutions. With an expansive inventory of power modules and chassis, coupled with our years of applied experience and expertise, Sager can provide a configured solution that meets your precise power requirements.
What if you take the power supply outside the system and employ an external power supply? This removes the heat the power supply produces and eliminates the space required for the power supply from the system enclosure. Now the consideration becomes how the power supply connects to the system enclosure and the loads within the system. One of the critical issues here is choosing an appropriate connector for the system before choosing the external power supply. External power supplies have a designated standard output connector based on the power level and the manufacturer of the power supply. If the connector in the system does not match the connector on the power supply, a modified standard version of the power supply may be required to have the proper mating connector attached, with minimum order quantities and potentially higher costs.
A final consideration is whether a design relies on batteries as a primary or secondary power source. Batteries, which accept, store and release electricity on demand, power everything from small electrical devices to medical devices, robotics, electric vehicles, and more. As automation and electrification becomes increasingly common across all industries, a design engineer will need to consider rechargeability, energy density, power density, shelf life, safety, form factor, cost, and flexibility when deciding which battery solution to use. Sager Electronics’ growing line card of battery solutions and custom battery pack capabilities can help solve your battery design requirements.
With a world-class line card in interconnect, power, and electromechanical products, and expert technical sales and support, Sager has the standard, custom, and modular power products, and solutions for any power system design.