Pre-switching, a New Contrast to Hard-switching, Eliminates Switching Losses With AI

October 10, 2021 by Ikimi .O

A novel "pre-switch" architecture may allow designers to break free from hard-switching constraints.

Pre-Switch, a Silicon Valley-based company addressing the issues of hard-switching transistor losses, recently announced its expansion into a new facility. This expansion also entails a consequent increase in the company's staff base to strengthen its design, licensing, in-house manufacturing, and sales.

As its name suggests, Pre-Switch is offering something called "pre-switching" technology that leverages artificial intelligence (AI) to eliminate switching losses. This article explores Pre-Switch’s technology and reveals how designers can incorporate it into several power electronics applications.


Understanding Pre-Switch’s New Technology 

Pre-switching technology uses an auxiliary forced-resonant architecture to enable soft-switching. This architecture minimizes switching losses and maximizes switching efficiencies by ensuring an almost-zero overlap between the voltage and current switching waveforms. The technology achieves this unprecedented efficiency by “pre-switching” a standalone, small, and low-cost transistor with accurate timing before soft-switching its target transistor


Voltage-current waveform in pre-switching technology

Voltage-current waveform in pre-switching technology. 


Since timing is essential for low-switching losses, conduction losses, and high-switching frequencies, Pre-Switch incorporates a Pre-Flex AI chip to learn and adapt to system changes on a cycle-by-cycle basis. This chip is said to ensure soft-switching regardless of transistors’ topology, temperature, input voltage, manufacturing tolerance, and output conditions.

Additionally, Pre-Switch Blink, a Pre-Flex platform-based safety feature, can halt the operation of a power converter in the event of an electrical fault. With the aid of a Pre-Flex-embedded communications port, Blink provides error-related reports to an independent host, on which engineers can further act.


Pre-switch architecture

Pre-switch architecture. 

Pre-Switch claims its technology reduces switching losses by up to 95 percent over conventional soft-switching alternatives. This technology is also said to significantly minimize electromagnetic interference (EMI) in various switching operations. In addition, pre-switching offers designers the opportunity to select the ideal dV/dt for their applications and a cycle-by-cycle-based fault detection system, providing higher reliability for power conversion.


Hard-switching, Soft-switching, and Pre-switching: What's the Difference?

Transistors including thyristors, IGBTs, BJTs, and MOSFETs, are essential elements for power conversion in electronic applications. These three-pin devices allow current flow between two pins while the input voltage on the third controls the flow. Thus, transistors allow voltage-induced current flow in power systems due to on-off-state-related switching.

There are two conventional switching architectures: hard- and soft-switching. While hard-switching directly turns target transistors on and off, soft-switching requires an extra external circuit to prevent current and voltage waveforms from overlapping during target transistor commutation.



The absence of an external circuit and accurate cycle-by-cycle timing during transistor commutation leads to switching losses in hard-switching. These losses are commonly higher in high-voltage transistors. Hard-switching exhibits other drawbacks, including low efficiency, high system-level operation costs, low switching frequency, high EMI, and increased size and weight of components.


Voltage-current waveform in hard-switching technology

Voltage-current waveform in hard-switching technology. 


Regardless of these drawbacks, designers can still incorporate this topology into a wide range of power converter applications by trading off switching frequency for lower switching losses, higher switching efficiencies, or lower thermal dissipation.



Unlike hard-switching, soft-switching employs a self- or forced-resonant circuit to ensure appropriate transistor commutation timing. Self-resonant soft-switching topology offers significant improvements over hard-switching, including minimized switching loss, increased efficiency, and EMI reduction.

However, designers can only incorporate this topology into non-isolated power converters with low input voltage and output load range. Consequently, self-resonant soft-switching topology has a limited DC/DC converter-related application range.

On the other hand, by employing several inputs such as transistor voltages, currents, input voltage, and load, forced-resonant soft-switching can adequately calculate the appropriate timing for the ideal voltage-current waveform overlap to eliminate switching losses. 



Pre-switching has evolved from forced-resonant soft-switching. As such, it offers higher performance-related capabilities, including an AI-based chip that ensures higher accuracy in transistor commutation timing, an advanced safety feature, and significant EMI reduction. By offering designable dV/dt per switching cycle, this technology is useful for high switching, wide bandgap devices.


Pre-switch adaptive soft-switching topology

Pre-switch adaptive soft-switching topology. 

Incorporating Pre-switching Into Electronic Designs 

There are two common options for pre-switching in real-world applications, including efficiency and cost conditions. In the efficiency condition, designers retain a constant switching efficiency to exploit reduced switching losses. Conversely, designers keep switching losses the same to allow for higher switching frequencies in the cost condition. 

By using Pre-Flex loss reduction, Pre-Switch says designers can achieve higher system efficiencies. For example, a 95 percent efficient power converter can achieve a higher efficiency of 97 percent by incorporating Pre-Switch’s technology, which reduces switching losses by 80 percent.

Employing pre-switching technology, designers can still achieve higher frequencies with conventional transistors, trading off switching losses for low costs. For example, the technology can scale up system efficiencies by five times, which cuts passive component size and weight by a third and reduces cost by 50 percent. 


The Role of Pre-switching in SiC and GaN MOSFET Adoption 

Pre-switching technology can use low-cost IGBTs to soft-switch high-speed SiC and GaN systems. Transistors have undergone rapid development through the years to ensure low switching losses and high switching frequencies in a host of power electronics applications.

In recent times, SiC and GaN MOSFETs have been the industry-leading transistors for various power conversion applications, including DC/DC, AC/DC, and DC/AC conversions. However, these devices still face some challenges when incorporated into conventional switching architectures (e.g., hard-switching) in real-world applications, such as high switching frequency-induced noise, high cost, low efficiencies, and significant size and weight.

By integrating these MOSFETs into Pre-Switch's architecture, designers may efficiently handle these challenges, breaking free from hard-switching constraints.


All images used courtesy of Pre-Switch