MuxCapacitor: the High Efficiency Solution for DC-DC and AC-DC Converters

Article By : M. Di Paolo Emilio

We take a look at Helix Semiconductors latest MuxCapacitor conversion IP which allows Helix to build highly integrated power ICs, usable in a variety of applications that require AC-DC or DC-DC power conversion

MuxCapacitor® is a proprietary voltage conversion technology developed by Helix Semiconductors. Thanks to its high efficiency, the MuxCapacitor conversion IP allows Helix to build highly integrated power ICs, usable in a variety of applications that require AC-DC or DC-DC power conversion. By implementing this technology through a high voltage SOI CMOS process, devices are obtained that can support input voltages up to 400 V DC, suitable for use in most applications where conversion from alternating current to direct current is necessary. The AC-DC converters developed by Helix are suitable for developing power supply solutions both with and without transformers, ensuring an average end-to-end efficiency of over 95% in both cases.

MuxCapacitor technology also proves to be particularly useful in managing power dissipation under load-free conditions. When the load absorption is zero, the proprietary IP of Helix has an absorption of less than 5 mW, without producing any effect on the value of the output voltage, which remains at the required value. Another important family of devices developed by Helix Semiconductors concerns the DC-DC converters, mainly aimed at intermediate voltage conversion applications.

These converters have input voltages between +24 V DC and +60 V DC, with an average efficiency of over 94% and absorption in the absence of a load of less than 5 mW. The typical applications of Helix AC-DC voltage converters are as follows: USB-C compatible output voltages, smart outlets, IoT and IIoT gateways, remote sensors, smoke and CO detectors. DC-DC converter applications include telecom blades, data centers, cloud servers and racks, PoE devices, wireless access points security cameras, VoIP phones, industrial controllers, HVAC, IoT & IIoT Gateways.

An overview of MuxCapacitor technology

In the last few years, there has been a proliferation of electronic devices and applications, which has resulted in a growing demand for power management solutions, both in direct and alternating current.

To continuously reduce power absorption, required by both industrial and consumer applications, it is necessary to design solutions and devices that offer very high efficiency, minimizing losses and power dissipation. Additionally, aspects related to current regulations, such as those that are purely ecological, should not be overlooked in contributing to environmental protection.

In this context, the MuxCapacitor technology (briefly, MuxCap™) developed by Helix Semiconductors represents a break with traditional solutions. MuxCap achieves a very high level of efficiency in all load conditions, combined with minimum energy waste. The high efficiency obtainable through the MuxCap capacitive conversion technique can also be combined with another proprietary Helix technology: CapIso™. CapIso offers a solid-state capacitive isolation, eliminating the need for bulky and expensive transformers in the design of AC-DC converters and isolated DC-DC converters. The use of MuxCap and CapIso technologies, therefore, makes it possible to obtain straightforward, compact, and highly efficient solutions for power conversion.

The power efficiency, expressed in percent, obtainable with a solution based on the MuxCap technology is shown in Figure 1. As can be seen, the blue curve corresponds to a very high-efficiency value and remains almost constant as the load varies (also the load is expressed in percent). The red curve refers instead to a common type of solution, based on a traditional magnetic-based technology. It should be noted that the second solution achieves efficiency values comparable to those of the MuxCap solution only for a load usage of over 50%, while for lower load values the efficiency is much lower.

Figure 1

Figure 1: comparison, in terms of efficiency, between a MuxCap solution and a traditional one [Source: Helix Semiconductor]

The efficiency curve highlights the advantage of MuxCap power delivery. Not only is the efficiency extremely high, but there is no efficiency penalty at low operational loads. Helix MuxCap chipsets include up to three stages, where each MuxCap stage consumes less than 1μA quiescent operating current. MuxCap, based on a switched-capacitor charge pump technology, achieves greater than 98% efficiency and is suitable for both isolated and non-isolated, AC-DC and DC-DC, buck or boost power conversion solutions.

The upper side of Figure 2 shows an application diagram relating to a generic buck or boost voltage converter, based on the MuxCapacitor technology. As can be seen, only a few external flying capacitors and a capacitor connected between the output voltage VOUT and ground are needed to obtain a compact and integrated single-stage voltage converter. As an example, the lower side of Figure 2 shows two configurations (or networks) of external capacitors, through which it is possible to achieve, respectively, a voltage gain of 1.5 or 0.66.

Figure 2

Figure 2: application diagrams related to the MuxCap converter, in boost and buck configurations [Source: Helix Semiconductor]

On the other hand, figure 3 shows a typical scheme related to the combined use of MuxCap and CapIso technologies. The IP built with MuxCap technology are implemented both on the primary and the secondary side of the chipset, while the inner circuit made with CapIso technology provides a capacitive type of barrier. A solution of this type, which has obtained the approval of the Underwriters Laboratories (UL) with regards to safety aspects, offers the critical benefit of eliminating the need for an isolation transformer.

Figure 3

Figure 3: scheme of combined use of MuxCap and CapIso technologies [Source: Helix Semiconductor]

Helix MxC® 200 and MxC 300 product families

The power conversion solutions offered by Helix can be divided into two families, MxC 200 and MxC 300. The Helix Semiconductors MxC 200 family consists of several monolithic, configurable, high-voltage switch capacitor integrated circuits, targeted for use in both non-isolated and isolated, buck or boost DC-DC converter applications. These types of devices are particularly suitable for applications such as machine vision, cameras, PoE devices (wireless access points, security cameras, VoIP phones), telecom applications, industrial control, HVAC, electric and hybrid automobiles, IoT and IIoT gateways.

The MxC 200 family of ICs supports seamless interface to low voltage Point of Load (PoL) regulators to provide highly efficient DC-DC converter solutions with 12V to 57V input voltages and regulated or non-regulated PoL solutions. Buck converters, depending on the specific version, convert an input voltage to either 3 output voltages in series, each a division of 2 of the input, or a single output voltage of a divide by 4 of the input. For example, a nominal 48V input voltage is converted to 24V, 12V and 6V output voltages, or a 48V input voltage to a single 12V output voltage. The boost converter features a multiply by 4, which can for example convert a nominal 12V input voltage to a 48V output voltage. All devices are composed of multiple (two or three) MuxCap stages. The MxC 200 family also includes a pair of devices that can be used to create an isolated buck or boost converter, which implements the same type of architecture shown in Figure 3. As mentioned before, the capacitive isolation barrier makes it unnecessary to use a transformer. The MxC 300 family includes a configurable chipset, designed to be used in AC-DC converters without transformers, featuring up to 65W of output power. Using a capacitive-type isolation barrier, it becomes possible to remove bulky transformers from the project, obtaining an improvement in power density from 5 to 7 times higher than the traditional solution, with a combined end-to-end efficiency of 94% or higher. The MxC 300 chipset consists of a Power Controller IC (MxC 310) located on the primary side of the AC-DC adapter and a Power Manager IC (MxC 300) located on the secondary side, with the task of reducing the output voltage value. Between the two ICs, there is the isolation barrier, made with CapIso technology. The chipset supports an output current up to 3.25V at 20V.


Through its proprietary and patented technologies, MuxCap and CapIso, Helix Semiconductors offers highly efficient capacitive power-transfer solutions with the highest power density, suitable for AC-DC and DC-DC, buck and boost voltage conversion applications. The possibility of eliminating the isolation transformer makes Helix solutions not only innovative but also advantageous in terms of cost and size reduction. Helix power solutions can meet even the most demanding applications involving AC-DC converters (such as cloud servers) or DC-DC converters (such as e-Vehicles, solar energy conversion, and data centers).

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