Depletion-Mode Field-Effect Transistors from ARK Microelectronics

Depletion-Mode Field-Effect Transistors from ARK Microelectronics

Depletion-mode? Only in the name. In practice, this is a transistor that starts working immediately — it doesn’t wait for a control signal.

Depletion-Mode Field-Effect Transistors – Why Are They Worth Knowing

In the semiconductor market, the vast majority of manufacturers focus on enhancement-mode MOSFETs, which are the typical “normally-off” devices. These transistors require a gate-source voltage to begin conducting. This behavior is convenient and safe, which is why it has become the standard in power electronics and digital circuitry.

However, alongside them exists a lesser-known but highly valuable group of devices — depletion-mode transistors, often referred to as “normally-on.” With zero gate-source voltage, these transistors already conduct current, and only an appropriate control voltage can turn them off. They are an excellent choice for applications that must operate immediately upon power-up or where minimizing losses in startup circuits is critical.

Why Are Depletion-Mode Transistors Less Popular?

The standard design philosophy in electronics prioritizes safe default states, meaning devices should remain off unless explicitly activated. This is exactly what enhancement-mode MOSFETs provide, which explains their dominance. Their mass production is optimized to deliver extremely low RDS(ON) values and outstanding switching performance. Depletion-mode transistors, on the other hand, are considered more specialized components — used in cases where the “normally-on” characteristic offers unique advantages. As a result, their market is smaller, but in certain applications they are the ideal solution.

Key Advantages of Depletion-Mode Transistors

• Normally-on operation – At zero gate bias the transistor behaves like a closed switch or resistor. This greatly simplifies circuits that must start operating without additional control electronics.
• Perfect for startup and auxiliary circuits – In switching power supplies, they can replace startup resistors, reducing power losses and part count while improving reliability and efficiency.
• Simple current sources and constant-load elements – Their inherent I–V characteristics make them suitable for compact, stable current sources or active resistors in analog circuits.
• Safety and fail-safe behavior – In many applications, a depletion-mode device ensures current flow even when the control circuitry is not yet active. It can serve as an “emergency-on” element, improving system robustness.
• Excellent properties for high-frequency designs – Low input capacitances make certain models suitable for RF and communication circuits.

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ARK Microelectronics – A Specialist in Depletion-Mode Transistors

ARK Microelectronics is the only company in China that consistently focuses on the design and development of depletion-mode field-effect transistors. While most semiconductor manufacturers limit their offerings to standard enhancement-mode devices, ARK has specialized for years in this technological niche, which requires unique expertise and dedicated fabrication processes. With a strong R&D foundation — including experienced engineers with long-standing industry backgrounds and close cooperation with leading technical universities in China and abroad — the company holds nearly 70 patents and full intellectual property rights for its products. This enables ARK Microelectronics to maintain a leading position in the Chinese market, offering solutions that serve as a real alternative to MOSFETs from major global manufacturers.

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Table 1. ARK Microelectronics Transistors in the Micros Offer