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Why use a modular power supply?

Tuesday, November 22, 2022

TDK-Lambda’s history with the design and manufacture of modular power supplies began in 1979 with the launch of the ML series - a world first. Over the next 40+ years new modular products have been developed and launched addressing medical applications, the need for higher power, communication options and more recently, lower audible noise. The latest product, the MU4 series, was announced in November 2022 featuring a low 1U profile and very low acoustic noise.

What is a modular power supply?

As the name implies, modular power supplies are factory assembled using pre-manufactured and pre-tested output modules, converters and subassemblies. The user only needs to determine their required output voltages and currents, signaling and overall power level. TDK-Lambda utilizes an on-line configurator (Quick Product Finder) to optimize the module selection and provide a unique part number for quoting and ordering purposes. Once a configuration is determined and an order placed, the assemblies are mounted into a chassis, given a final test and shipped.

Modular products are available from around 400W to upwards of 2,000W and offer 1 to 18 outputs.

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Figure 1: 4th generation Vega series launched in 2002 showing the modular concept

The advantages of using a modular power supply are numerous compared to a modified standard power supply or a complete custom design. I shall address these and include some examples.

No production set-up charges

Most power supply companies offering modular power supplies do not charge a set-up or configuration fee. Sophistication in a product selector can be tied to the manufacturing software to electronically configure a bill of materials and issue a work order to production. The pre-built assemblies stocking levels can be integrated in a just-in-time Kan-Ban system.

Automated Test Equipment (ATE) is flexible enough to fully test any combination of modules, signals and output power. The configurator software can be used to automatically program the ATE, often by reading a barcode on the production work order. The product rating label printer can be tied to the ATE to ensure a product has been tested thoroughly and successfully; a label cannot be printed unless the supply 100% meets the specification

No minimum order requirements

A modified standard power supply will often require modified printed wiring boards, custom transformers and magnetics, which in turn will likely require a MOQ from the component manufacturer. The use of modular power supplies with standard assemblies removes this requirement.

No engineering charges and flexibility

Modifying a standard product will often require non-recurring engineering charges. Using a modular power supply avoids this. If the system load requirements change during development, requiring more current or a different output voltage, another configuration can be easily created.

Safety certification

Most modular products have certification to the medical (IEC 60601-1) and industrial and I.C.T. (Information and Communication Technology) (IEC 62368-1) standards. The safety reports cover all the possible configurations, which takes a considerable effort and money by the manufacturer, but full series compliance ensures that any unit ordered will automatically have safety logos applied to the rating label.

Wide range output adjustment

Depending on the power supply topology that the manufacturer uses, the output voltage may be capable of adjustment across a wide range. Figure 2 shows the adjustment range of TDK-Lambda’s new MU4 series, this also provides seamless availability of any voltage from 3.3 to 104V in the configurator.

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Figure 2: MU4 output voltage ranges

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Figure 3: MU4 1U high modular power supply

No minimum loads, improved regulation and isolated outputs

A standard multiple output (non-modular) power supply will have a lower cost basis, due to its single board construction and one power transformer with multiple windings. The control circuit will use the highest power output for control and regulation purposes (via an optocoupler) to the converter control IC. The lower power outputs will often have increased load and cross regulation, requiring a minimum load on the main output. All the outputs may have a common 0V (return) connection which pre-determines their polarity – either positive or negative with respect to the 0V.

Modular products typically have independent control for each output voltage, this results in tighter regulation and allows for isolation between each output. This avoids the need for any minimum load requirements and allows the user flexibility to determine if the output is connected as a positive, a negative voltage or remain completely isolated from the other voltages in their system.

Signals and remote on/off functions

If the manufacturer offers signals or the ability to turn outputs on or off, this further increases flexibility. For example, individual outputs or the entire power supply can be turned off if the DC Good signal on a module displays an overload or fault condition.

Utilizing multiple single output power supplies

Another alternative to using a modular power supply is to use several single output power supplies. This may reduce the BOM cost but does come with some disadvantages and an increase in assembly time.

Each individual power supply will have its own leakage current, which is additive. It may not impact a system that is hard wired to the AC source, but certainly will impact the low leakage current requirements for medical and even some systems using a plug in AC line cord.

Similarly with meeting EMI and EMC. Multiple power supplies each have their own electromagnetic footprint, whereas the performance of a modular power supply is predetermined.

Cooling is simplified as the modular product can have an integral fan or fans. Modular products like the MU4 and QM series have been designed for low audible noise with sophisticated cooling techniques and algorithms. Mechanical assembly and wiring are easier with one power supply.

In summary, if you require more than one mid-power output in a system, it is certainly worth considering a modular power supply. Try the TDK-Lambda on-line configurator for yourself.

Power Guy

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