Product parameters
Operating frequency: 20kHz ~ 500kHz, suitable for high-frequency switching power supplies. Operating temperature: -40℃ ~ +125℃ (some models can reach +180℃). Storage conditions: -25℃ ~ +85℃, humidity 30% ~ 95% RH. Insulation withstand voltage: Usually requires AC 2000V, insulation resistance ≥200MΩ (tested at DC 500V).
* Product features The core competitiveness of ETD54 lies in the dual advantages of "power upgrade + performance optimization" brought by its large size. It not only inherits the general characteristics of the ETD series, such as standardized structure, process - friendliness, and high cost - effectiveness, but also comprehensively improves power density, high - frequency adaptability, heat dissipation potential, and electrical stability through the expansion of the magnetic core and the window. It has become the "universal core component" for medium - to - high - power (50 - 1500W) and high - frequency conversion scenarios (20 - 300kHz), taking into account both performance requirements and industrial production requirements. It is a highly suitable choice for high - power high - frequency transformers in the power electronics field. * Typical application fields
New energy photovoltaic and energy storage fields [Core high - power applications] Industrial switching power supply fields [Basic general applications] Industrial control and automation fields [Precisely adapted applications] Charging piles and in - vehicle electronics fields [Emerging expanded applications] Medical and security fields [Applications with strict safety regulations] Other commercial fields [Supplementary expanded applications]
* Product standards UL, RoHS, 3C, CQC
* Dimensions and specifications 
Type | Structure
Tурe | Dimension（mm） | Pin Row （mm） | Row Pitch
（mm） | OD Pin
（mm） | note | A | B | C | Pin | Pin Pitch | ETD54-001 | Vertical | 59.0 | 40.0 | 65.5 | 11+11 | 5.08 | 33.0 | Φ0.9 |
| ETD54-002 | Horizontal | 63.0 | 63.0 | 46.0 | 11+11 | 5.08 | 45.9 | Φ1.0 |
| ETD54-003 | Horizontal | 72.5 | 68.0 | 46.0 | 13+13 | 5.00 | 50.8 | Φ0.8 |
|
* The above are the commonly used bobbin styles of the company.,Other styles are not included for the time being.,Welcome to consult. Our company can customize high - frequency transformers of various specifications according to customers' requirements.
Performance Analysis of ETD54 Transformer The ETD54 is a mainstream model in the ETD series for high-frequency transformers, representing an upgrade in the power range. Its 'A' dimension of 54mm identifies the core size. It is based on MnZn ferrite core material and is suitable for switching power supply topologies operating from 20kHz to 300kHz, covering a power range of 50~1500W. Building upon the ETD49, it further enhances power density, magnetic flux capacity, and heat dissipation potential. It features both high-frequency low loss and strong structural adaptability, making it an excellent choice for medium-to-high-power power electronics conversion scenarios. The following provides a precise analysis across four key dimensions: core structure parameters, key performance, loss control, and environmental/reliability, highlighting its performance characteristics and design suitability post power upgrade. I. Core Structure and Basic Parameters The ETD54 continues the classic ETD series design of a round center leg and a wide winding window. The 54mm outer leg span (A dimension) provides a larger core cross-sectional area and winding space. The magnetic circuit design is optimized, balancing space utilization and electrical performance. Core parameters are standardized industrial values, suitable for mass production and standardized design. Parameter Item | Typical Industrial Value | Core Explanation | Outer Leg Span (A) | 54mm | Model's core size identifier, horizontal core span. | Core Material | MnZn Ferrite (PC40/PC44/PC95) | Standard PC40/PC44 (general high-frequency). PC95 for high-temperature scenarios. | Center Leg Diameter | Approx. 22~24mm | Round center leg shortens the average turn length, reducing copper loss and enhancing current-carrying capacity. | Effective Area (Ae) | Approx. 45~50mm² | 18%~25% increase compared to ETD49, offering greater magnetic flux capacity and supporting higher power levels. | Effective Path Length (Le) | Approx. 130~140mm | Low reluctance, ample design margin for inductance, allowing flexible adjustment of magnetizing inductance. | Winding Window Area (Wa) | Approx. 700~750mm² | 15%~20% increase compared to ETD49, supporting large wire gauge, multi-winding, or center-tapped designs. | Bobbin Pins | 10+10 / 12+12 | Adapts to complex winding configurations for multi-output, primary/secondary isolation. | Insulation Class | Class B/F/H | Standard B/F Class (130℃/155℃). H Class (180℃) customizable for high-temperature applications. |
II. Key Performance Analysis The core performance of the ETD54 revolves around medium-to-high power, high-frequency efficiency, and stable electrical characteristics. It achieves a triple upgrade over the ETD49 in power, current-carrying capability, and high-frequency adaptability, while retaining the advantages of the ETD series: process-friendliness and high parameter consistency. It is suitable for various medium-to-high-power high-frequency conversion topologies. 1. Power and Efficiency Characteristics
Wide Power Coverage: Adaptable across the full 50~1500W range, adjustable based on topology and cooling solutions – suitable for 50~300W in Flyback/Forward topologies, and 300~1500W in LLC resonant, Push-Pull, or Half-Bridge topologies. It is a core component choice for medium-to-high-power switching power supplies.
High Power Density: The compact 54mm outer leg span structure, combined with large Ae and wide Wa design, increases power output by 30%~50% compared to the ETD49 under similar volume, meeting the needs for equipment miniaturization and high integration.
High Efficiency Performance: Optimal balance between core loss and copper loss within the 20~300kHz operating range, with typical efficiency between 90%~96%. For ultra-high-frequency scenarios (200~300kHz), using PC50 core material can increase efficiency to 95%~96%, demonstrating significant low-loss characteristics.
2. Electrical Performance Characteristics
Inductance and Saturation Characteristics: A_L value approximately 2200~3200nH/N² (depending on air gap and core material), allowing flexible magnetizing inductance design for different topologies. Saturation flux density Bs ≈ 400~450mT at 25°C, maintaining 320~360mT at high temperature (125°C). Parameter drift is small, and magnetic saturation can be avoided by leaving sufficient design margin.
Leakage Inductance and Distributed Capacitance: Optimized window structure and magnetic circuit allow precise control of leakage inductance to 0.8%~2.5% (relative to magnetizing inductance), lower than ETD49. Distributed capacitance is <500pF, significantly reducing EMI interference during high-frequency operation and improving circuit stability. Suitable for topologies sensitive to leakage inductance like LLC resonant converters.
Insulation and Voltage Withstand: Primary/Secondary power frequency withstand voltage ≥3.5kV AC, impulse withstand voltage ≥10kV. Creepage/clearance distances comply with UL60950/EN61558 standards, meeting safety requirements for AC-DC isolated power supplies. Suitable for applications with stringent safety regulations like medical and industrial.
Current Carrying Capacity: The wide winding window supports large wire gauge or multi-strand parallel winding techniques. Primary rated current ≤20A, secondary rated current ≤50A. Good suppression of skin effect in high-current scenarios, without significant sharp temperature rise.
3. Thermal Performance Characteristics
Low Temperature Rise: The round center leg offers a large heat dissipation area. Symmetrical air channels are reserved between the core and bobbin. Under natural convection, continuous operation temperature rise is ≤35K (typical for 1000W LLC topology). With forced air cooling (small fan), temperature rise can be controlled to ≤25K. Heat dissipation potential is significantly better than ETD49.
Thermal Stability: MnZn ferrite Curie temperature ≥210°C. Within the wide temperature range of -40°C to +125°C, drift in core parameters like permeability and loss is <15%, with no significant performance degradation. Suitable for wide-temperature applications like industrial outdoor and new energy.
III. Core Logic of Loss Control Loss control is central to the ETD54 design. Through a triple approach of structural optimization, material matching, and process adaptation, it achieves comprehensive suppression of core loss, copper loss, and stray losses, ensuring low loss and high efficiency under high-frequency, high-power conditions. The specific control paths are as follows:
Core Loss Suppression: Standard use of low high-frequency loss MnZn ferrite; PC50 core material selected for ultra-high-frequency scenarios (200kHz+) to reduce hysteresis and eddy current losses. Optimized magnetic circuit design reduces core air gap fringing effects, avoiding additional core loss from local flux concentration.
Copper Loss Suppression: The round center leg shortens the average turn length, reducing winding resistance. The wide winding window supports large wire gauge winding; for high-current scenarios, multi-strand enameled wire (Litz wire) parallel winding is used to suppress skin and proximity effects, reducing the sharp increase in copper loss at high frequencies.
Stray Loss Suppression: Standardized winding processes ensure neat winding layering, reducing inter-winding leakage flux coupling. Adding shielding layers between primary and secondary windings reduces both EMI and stray losses caused by leakage flux. The clip-on core ensures tight fitting, avoiding leakage flux loss due to core gaps.
IV. Environmental Adaptability and Reliability The ETD54 is designed to industrial-grade standards, accommodating complex operating conditions and ensuring long-term stable operation. Its core reliability and environmental adaptability indicators meet stringent requirements in fields like industrial, new energy, and industrial control, making it a preferred component for high-reliability equipment.
Wide Temperature Adaptation: Operating temperature range: -40°C to +125°C; storage temperature: -55°C to +150°C. Adaptable to extreme high/low temperature conditions such as northern outdoor environments, new energy photovoltaic systems, and industrial control cabinets.
Mechanical Reliability: Clip-on core fixation structure, vibration resistance rating ≥10g (complying with GB/T 2423), suitable for vibrating environments like industrial production lines, vehicle-mounted, and outdoor equipment. The bobbin uses high-temperature resistant, flame-retardant PBT material (UL94 V-0 rating), eliminating open flame risk.
Long-Term Stability: Standardized mold production controls core air gap and winding parameter tolerances within ±5%~±8%, ensuring high consistency in mass production. Insulation materials are resistant to aging and humidity; under continuous operation for 5000h at 90% relative humidity (40°C), performance degradation is <5%.
Interference Resistance: Low leakage inductance and low distributed capacitance design, combined with shielding layer techniques, result in EMI radiation ≤30dBμV/m (complying with EN55032). This often eliminates the need for additional complex EMI filtering circuits, simplifying overall machine design.
V. Topology Adaptability Analysis The structure and performance design of the ETD54 adapt to mainstream high-frequency switching power supply topologies. Performance can be maximized for different topologies by adjusting core air gap, winding turns ratio, and winding techniques. Key topology adaptation points are as follows:
Flyback / Forward Topology (50~300W): Add air gap (0.2~0.8mm) to suppress magnetic saturation. Forward topologies require adding a reset winding. Suitable for medium-low power, multi-output industrial power supply scenarios.
LLC Resonant Topology (300~1500W): Reduce air gap (0~0.3mm) to increase magnetizing inductance. Utilize low leakage inductance characteristics to match LLC resonant tank parameters, achieving Zero Voltage Switching (ZVS) and significantly improving efficiency. A core topology for new energy and high-power industrial power supplies.
Push-Pull / Half-Bridge Topology (500~1500W): Symmetrical winding design ensures accurate primary/secondary turns ratio. Moderate core air gap (0.3~0.5mm). Suitable for high-power, high-voltage input conversion scenarios like photovoltaic inverters and energy storage converters.
Drive Transformer Topology (Low Power): Leverages high insulation withstand voltage and low leakage inductance characteristics. Suitable for IGBT/MOSFET driver circuits, providing electrical isolation between control and power circuits, ensuring accurate drive signal transmission.
VI. Performance Summary The ETD54 (outer leg span 54mm), as a power-upgraded model in the ETD series, has core advantages of wide 50~1500W power coverage, 20~300kHz high-frequency adaptability, and high power density with low loss. Building upon the ETD49, it achieves a triple upgrade in power, current-carrying capacity, and heat dissipation potential by increasing the core cross-sectional area and winding window. Simultaneously, it retains the core characteristics of the ETD series: structural standardization, process friendliness, and high safety regulation compatibility. Its performance adaptability covers medium-to-high-power high-frequency conversion needs across multiple fields including industrial, new energy, industrial control, and medical. It is a core, preferred model for devices like 300~1500W switching power supplies, photovoltaic micro-inverters, energy storage converters, and servo drives. During design, simply matching the core material, air gap, and winding process to the topology type is sufficient to maximize its performance advantages of high-frequency efficiency, low EMI, and high reliability.
Core Features of ETD54 Transformer The ETD54 is a mainstream upgraded model in the ETD series for high-power high-frequency transformers. Identified by its core dimension of 54mm, it continues the classic series structure of a round center leg and a wide winding window. Building upon the ETD49, it delivers comprehensive improvements in core cross-sectional area, winding space, and power handling capacity. Suitable for 20~300kHz high-frequency operation and power levels from 50W to 1500W, it combines core advantages such as high power density, high-frequency low loss, strong structural adaptability, and excellent reliability. It is a preferred general-purpose model for medium-to-high-power power electronics conversion scenarios. The following concisely presents its core features from four dimensions—structural design, performance, process/cost, and scenario adaptation—highlighting its differentiated advantages post-power upgrade: I. Structural Design: Large Space, High Utilization, Adapts to Complex Winding Needs
Enhanced Dimensions, Expanded Resources: Outer leg span 54mm, effective cross-sectional area Ae≈45~50mm², winding window area Wa≈700~750mm², representing increases of 18%~25% and 15%~20% respectively compared to ETD49. Magnetic flux capacity and current-carrying space are significantly increased, supporting medium-to-high-power output.
Optimized Classic Structure: The round center leg design shortens the average turn length, reducing copper loss. The wide window accommodates 11+11/13+13 pin bobbins, supporting large wire gauge, multi-winding, center-tapped, and multi-output designs, meeting winding configuration needs for isolated/non-isolated and complex topologies.
Compact and Thermally Adaptable: Clip-on core fixation ensures a compact, vibration-resistant structure. Symmetrical air channels are reserved between the core and bobbin, providing a large heat dissipation area. It balances equipment miniaturization design and thermal layout without occupying excessive extra space.
Standardized Magnetic Circuit: Effective magnetic path length Le≈130~140mm, featuring low reluctance and ample design margin for inductance. Magnetizing inductance is adjustable flexibly, adapting to parameter design requirements of different topologies.
II. Performance: High-Frequency Efficiency, High Power, Enhanced Electrical Stability
Broad Power & High-Frequency Coverage: Covers 50~1500W power range, adaptable to 20~300kHz high frequencies. For ultra-high-frequency scenarios (200~300kHz), it can be paired with low-loss PC50 core material. Typical operating efficiency is 90%~96%, representing a 2%~3% efficiency improvement over ETD49, with better core and copper loss balance.
Superior Electrical Characteristics: A_L value approximately 2200~3200nH/N². Leakage inductance is precisely controlled at 0.8%~2.5% (relative to magnetizing inductance), and distributed capacitance is <500pF—both superior to ETD49. This significantly reduces high-frequency EMI interference and improves circuit operational stability. Saturation flux density Bs≈400~450mT at 25°C, with parameter drift <15% across a wide -40°C to +125°C temperature range, showing no significant performance degradation.
High Current & High Voltage Withstand: The wide window supports large wire gauge/multi-strand parallel winding. Primary rated current ≤20A, secondary ≤50A, with good skin effect suppression under high current. Primary/secondary power frequency withstand voltage ≥3.5kV AC, impulse withstand voltage ≥10kV. Creepage distances comply with UL/EN standards, offering stronger safety regulation adaptability.
Outstanding Thermal Potential: The round center leg provides a large heat dissipation area. Temperature rise is ≤35K under natural convection and can be reduced to ≤25K with forced air cooling, representing a 10%~15% reduction compared to ETD49. Reliability is higher in high-temperature conditions, supporting long-term full-load operation.
III. Process & Cost: Standardized, Easy to Manufacture, Balancing Cost-Effectiveness and Consistency
Winding Process Friendly: The wide window reduces the difficulty of automated winding, supports multi-strand enameled wire and Litz wire winding, and adapts to the process requirements of high-current scenarios, resulting in high production efficiency.
High Standardization: Both the core and bobbin are industry-standard, common components, offering low procurement and replacement costs. There are no redundant custom designs, aligning with the ETD series' core positioning as an "Economic Transformer Design."
Excellent Parameter Consistency: Standardized mold production controls key parameter tolerances—such as core air gap, winding turns ratio, and inductance value—within ±5% to ±8%. Performance variation in mass production is minimal, meeting the needs for scaled industrial product supply.
Flexible Insulation Customization: Standard insulation class B/F (130°C/155°C). Customizable Class H (180°C) high-temperature resistant insulation materials are available, adapting to special high-temperature conditions like new energy and industrial outdoor applications without major structural changes.
IV. Scenario Adaptation: Broad Topology Compatibility, Core Choice for Medium-High Power Across Fields
Full Topology Adaptability: Adapts to Forward/Flyback topologies in the medium-low power range (50~300W) and perfectly matches LLC Resonant/Push-Pull/Half-Bridge topologies in the medium-high power range (300~1500W). Performance for different topologies can be maximized simply by adjusting the air gap (0~0.8mm), without needing to change the core model.
Core Adaptability Across Multiple Fields: Focuses on three core areas—New Energy, Industrial Power Supplies, and Industrial Control Equipment—while also covering scenarios with stringent safety regulations like Medical and Security. It is a mainstream preferred choice for 300~1500W switching power supplies, PV microinverters, energy storage converters, servo drivers, and IGBT drivers.
Strong Operating Condition Adaptability: Designed to industrial-grade standards, with vibration resistance rating ≥10g. Operating temperature -40°C to +125°C, storage temperature -55°C to +150°C. Can adapt to complex conditions involving high/low temperatures and strong vibration, such as outdoor environments, industrial control cabinets, and vehicle-mounted applications. Performance degradation is <5% after 5000 hours of continuous operation at 90% humidity.
Equipment-Design Friendly: Low leakage inductance and low distributed capacitance characteristics reduce EMI interference, often eliminating the need for additional complex filtering circuits. This simplifies the overall equipment design process and reduces overall R&D and production costs.
Core Application Scenarios of ETD54 Transformer As a mainstay model in the ETD series for medium-to-high power high-frequency transformers, the ETD54 leverages its core characteristics—wide power coverage (50~1500W), high-frequency adaptability (20~300kHz), low leakage inductance, and high voltage withstand capability—to be compatible with all mainstream topologies like Forward, Flyback, LLC Resonant, and Push-Pull. It primarily targets the 300~1500W medium-to-high power high-frequency conversion segment, while also meeting requirements for wide temperature operation, vibration resistance, and high safety standards. It is widely used in core fields such as New Energy, Industrial Power Supplies, and Industrial Automation and Control, and also covers scenarios with stringent safety regulations like Medical and Security applications. It serves as a versatile and preferred component for medium-to-high power power electronic equipment. The following details its core applications and adaptation specifics across different fields, highlighting three key aspects: power matching, topology compatibility, and operational condition suitability. I. New Energy Photovoltaics (PV) and Energy Storage: 「Core High-Power Applications」 Adapting to the needs for high-frequency efficiency, isolation, and noise immunity in new energy power conversion, it is a core power conversion component in PV and energy storage devices above 300W, representing the most mainstream high-value application scenario for the ETD54.
PV Microinverters: Used in the DC-DC/DC-AC conversion stages of residential/commercial 300~1500W microinverters, facilitating PV panel energy conversion and grid isolation. Its low leakage inductance characteristic is well-suited for resonant topologies, enhancing overall system efficiency and grid interconnection stability.
Energy Storage Converters (PCS): A key conversion component in small-scale energy storage cabinets and commercial/industrial energy storage modules. It adapts to the 300~1500W power range for lithium battery charging/discharging, with its wide input voltage range fitting the operational profiles of energy storage systems, ensuring charge/discharge efficiency.
Portable/Residential Energy Storage Systems: Employed in AC-DC/DC-AC conversion for high-power outdoor energy storage and residential integrated energy storage units. It balances compact structure with high power output, meeting the high-frequency and high-efficiency requirements for mobile power supply.
PV Charge Controllers: Used for voltage conversion and isolation in medium-to-high power PV charging equipment, adapting to the high-power generation characteristics of PV panels to improve energy utilization.
II. Industrial Switching Power Supply Field: 「Fundamental & Versatile Applications」 Covers various 300~1500W industrial-grade standardized switching power supplies, adapting to the core needs of industrial equipment for stable power, wide temperature tolerance, and vibration resistance. It is a mainstream choice for industrial power supply systems.
Industrial AC-DC Power Supplies: Used in 300~1500W high-power industrial power supplies and multi-output power supplies. Suitable for powering automated production lines and industrial control cabinets, meeting requirements for wide temperature operation (-40℃~+125℃) and vibration resistance in industrial environments.
Telecom/Data Center Power Supplies: Applied in distributed power supplies for communication base stations and high-power backup power supplies for data center equipment rooms. Its high-frequency, low-loss characteristics support 24/7 continuous operation, helping to reduce data center energy consumption.
Server/Industrial PC Power Supplies: Used in high-power density power supplies for medium-to-high power servers and industrial computers. Its compact structure suits equipment miniaturization designs, and its high current-carrying capacity meets the high-power supply demands of industrial control equipment.
Industrial High-Power Adapters: Designed for specialized high-power adapters for industrial equipment and power supplies supporting charging piles. Supports high-voltage/high-current output while ensuring isolation safety standards and long-term operational reliability.
III. Industrial Control and Automation: 「Precision Adaptation Applications」 Adapts to the needs of industrial control equipment for low leakage inductance, high stability, and signal isolation, ensuring precise control and reliable operation of servo and frequency conversion devices above 300W.
Servo Drives / Inverters: Serves as the drive power supply and isolation transformer in medium-to-high power servo motors and inverters (300~1500W range). Low leakage inductance minimizes EMI interference on control signals, enhancing control precision.
IGBT/MOSFET Gate Drive Transformers: Used in the drive stage for industrial high-power semiconductor devices. Its high voltage withstand capability (≥3.5kV AC) provides electrical isolation between control and power circuits, ensuring accurate drive signal transmission and improving device operational stability.
CNC Equipment Power Supplies: Employed in switching power supplies for medium-to-high power CNC machines, laser engravers, and other CNC equipment. Balances high power output with the ability to withstand complex industrial site conditions, offering excellent vibration and temperature resistance.
Industrial Welder Auxiliary Power Supplies: Used for auxiliary power and power conversion in small industrial welders. Adapts to the high-frequency operating characteristics of welders, with high current-carrying capacity meeting the high-current demands.
IV. Charging Pile and Vehicle Electronics: 「Emerging & Expanding Applications」 Adapts to the core needs for high power, high frequency, and compactness in new energy charging and vehicle electronics, aligning with the trend of charging pile miniaturization and the operational requirements of vehicle-mounted equipment.
Portable EV Charging Piles: A core component in the AC-DC conversion stage of 3.3kW/7kW portable charging piles. Balances high power with a compact structure to meet the portability requirements for outdoor charging.
E-bike Fast Charging Piles: Used for voltage conversion and isolation in high-power centralized fast-charging piles for electric bicycles. High-frequency, high-efficiency characteristics improve fast-charging efficiency and reduce temperature rise in the charging pile.
Vehicle-Mounted High-Power Supplies: Used for conversion and isolation in high-power vehicle-mounted power supplies for commercial vehicles and construction machinery. Adapts to the wide temperature and vibration-prone conditions of the vehicle environment, ensuring reliable equipment operation.
V. Medical and Security Fields: 「Stringent Safety Regulation Applications」 Leveraging its high insulation voltage withstand, low leakage current, and high stability, it meets the safety standards and demanding operational requirements of medical and security equipment, suitable for medium-to-high power devices above 300W.
Medical High-Power Isolated Power Supplies: Provides isolated power for medium-to-high power medical diagnostic and therapeutic equipment. Complies with medical safety standards; low leakage current reduces risk to patients, and high stability ensures precise operation of medical devices.
Centralized Security System Power Supplies: Used in outdoor high-power integrated security units and centralized power supplies for multi-channel surveillance systems (300~1500W range). Its wide-temperature characteristic suits outdoor high/low temperature conditions.
Medical Aesthetic Equipment: Serves as the power conversion component in high-power medical laser and radiofrequency equipment. Balances high voltage safety standards with a compact structure to meet the requirements of medical aesthetic devices.
VI. Other Commercial Applications: 「Supplementary & Expanding Applications」 Adapts to various commercial high-power power electronic devices above 300W, meeting design needs for high frequency, high efficiency, and long-duration operation.
Commercial Display Equipment: Used in high-power supply units for large commercial displays and outdoor advertising machines. Low-loss characteristics suit 24/7 operation, reducing temperature rise and power consumption.
Industrial Microwave Equipment: Employed in auxiliary power supplies and power conversion for small industrial microwave equipment. High-frequency adaptability matches the operating characteristics of microwave devices, and high power density fits compact equipment designs.
Air Source/Heat Pump Controllers: Used in the high-power controller power supplies for air source water heaters and heat pump systems. Adapts to the high-frequency operation and outdoor installation conditions of such equipment, improving energy conversion efficiency.
|
