Power Supply Unit – Linear Power Supply

Brief description:

Linear power supply is a traditional power supply solution that achieves stable DC output through linear regulation.

The core working principle of a linear power supply can be divided into two steps: first, using a power frequency transformer to reduce 220V AC power to the required voltage value, and then converting it into rough DC power through a rectification and filtering circuit; Subsequently, the linear regulator (a power transistor operating in the linear amplification region) acts as a dynamically variable resistor, automatically adjusting its voltage drop by detecting the output voltage in real-time and comparing it with the reference voltage, thereby absorbing excess energy and ultimately outputting highly stable and pure DC current.

The main advantages of this scheme are excellent output characteristics: extremely low ripple and noise (usually below 1mV), no high-frequency interference generated by switching power supplies, almost zero electromagnetic radiation, and simple circuit structure, high reliability, and fast dynamic response. However, its inherent drawbacks are low conversion efficiency and large size. Based on its “clean” but “inefficient” characteristics, linear power supplies are mainly used in fields such as medical equipment, industrial control, audio and testing, and small household appliances.

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Details description

☷ Product Description

Our switching power supply adopts pulse width modulation (PWM) and high-frequency switching conversion technology, which achieves efficient energy conversion and precise voltage regulation output through precise circuit control. The product series covers various types such as compact rail power supplies, open board power supplies, and sealed waterproof power supplies, meeting the needs of different installation environments.

▶ Core topology：By adopting mature and reliable advanced topology structures such as Flyback, Forward, Half Bridge/Full Bridge, and LLC resonance, the efficiency and cost of different power ranges are optimized.

▶ key components：Using internationally renowned brands such as Infineon, TI, STM for MOSFETs and controllers, coupled with high-performance high-frequency transformers and low ESR solid-state capacitors, to ensure product reliability and longevity from the source.

▶ Precision control and protection：Built in precision feedback loop, achieving pure output with low ripple noise and high load/linear adjustment rate. It has comprehensive protection functions, including overload (OLP), overvoltage (OVP), short circuit (SCP), and over temperature (OTP) protection, to ensure the safety of power supply and terminal equipment.

▶ Design and Compliance：The product design complies with international safety and electromagnetic compatibility (EMC) standards such as UL, CE, CB, RoHS, and some models meet stringent requirements such as Class I (Div 2) or medical (BF type).

☷ Product Advantages

The core function of AC/AC communication adapter

1. Voltage conversion: This is the most direct function. It reduces the high voltage of the mains power (such as 220V AC in China and 110V AC in the United States) to the safe low voltage required by the equipment (such as 16.5V, 9V, 18V, etc. as you mentioned).

2. Electrical isolation: This is the most critical and important safety function of AC/AC adapters. It uses an internal transformer and the principle of electromagnetic induction to completely isolate the input side (primary coil) and output side (secondary coil) electrically. There is no potential difference between the output voltage and the ground. Even if you accidentally touch one end of the output line, it will not form a circuit with the ground, thus avoiding the risk of electric shock and greatly improving the safety of device use. Isolation can effectively block surges, peak voltages, and noise interference in the municipal power grid, providing a “clean” power source for precision electronic equipment in the backend and extending equipment lifespan.

3. Design tradition and cost: For some mature devices, their internal circuit boards already integrate rectification, filtering, and DC-DC voltage stabilization modules. Continuing to use simple and reliable AC/AC adapters can reduce the cost of the adapter itself.

▶ Heat dissipation considerations: Placing the rectification and voltage stabilization circuits that generate heat on the motherboard inside the device can utilize the larger space and casing of the device itself to dissipate heat, rather than concentrating all the heat in a small adapter.

▶ Anti interference capability: Simple power frequency transformers are not sensitive to external electromagnetic interference and may be more reliable in certain noise sensitive applications.

▶ Safety: For a type of electrical appliance (with a metal casing that needs to be grounded), separating the “coarse adjustment” (voltage isolation) and “fine adjustment” (rectification and stabilization) of the power supply is a classic and safe design solution.

The fundamental difference from AC/DC adapters

To better understand the function of AC/AC adapters, comparing them with AC/DC is a very effective method:

Characteristics	AC/AC Adapter	AC/DC Adapter
Output current type	Alternating current	Direct current
Core component	Power frequency transformer	Transformer+rectifier bridge+filtering capacitor+(voltage regulator circuit)
Essence	Isolation step-down transformer	Switching power supply or linear power supply
Output voltage characteristics	Usually it is non regulated, and the voltage may fluctuate slightly depending on the load	Usually it is regulated, and the output voltage remains stable at the nominal value
Weight and volume	Heavy and large (due to iron core and copper wire transformer)	Light and small (especially switch mode power supply)
Efficiency	Relatively low	Relatively high
Application Logic	I am only responsible for providing safe low-voltage AC power, and you can do the rectification and voltage stabilization yourself	I will directly provide you with the stable DC power required for the device, and you can use it immediately

Some models have passed UL certification and comply with UL1310 safety specifications (UL file number E310452)

Model	Input			Output
Model	V ac	Hz	A or W	V ac	VA
ETL-AA025x-W165152	120	60	0.3A	16.5	25
ETL-AA025x-W090277	120	60	0.3A	9.0	25
ETL-AA020y-W090223	120	60	0.3A	9.0	20
ETL-AA040x-W165240	120	60	50W	16.5	40
ETL-AA050X-W165300	120	60	0.50A	16.5	50
ETL-AA0502-W180278	120	60	0.59A	18	50

Note: x=1,2,3 or 4； y=1, 2, 3, 4, A, B, C or D

☷ Application Scenarios

Our switching power supply is the “power heart” of the following fields, providing stable and clean DC power supply:

▶ Industrial Automation：PLC、 Control power supply for servo drives, stepper motors, industrial robots, sensors, I/O modules, and touch screen HMI.

▶ Communication and Network Infrastructure：5G base stations, routers, switches, servers, fiber optic transceivers, and backup power systems for data centers.

▶ Intelligent Manufacturing and Mechanical Equipment：CNC machine tools, laser engraving machines, 3D printers, packaging machinery, textile machinery, production line equipment.

▶ Intelligent Buildings and Security：Access control system, building intercom, video surveillance (CCTV), alarm system, LED lighting driver.

▶ Medical and laboratory equipment：Medical diagnostic equipment, bed monitoring devices, laboratory analytical instruments (requiring medical certification models).

▶ Transportation and New Energy：Rail transit electronic system, electric vehicle charging facilities, photovoltaic monitoring system, unmanned aerial vehicle ground station.