An optical coupler, also known as an opto-isolator or optocoupler, is a device that transmits electrical signals using light. It typically consists of an infrared light-emitting diode (LED) and a photosensitive semiconductor, both housed in the same package. When a signal is applied to the input, the LED emits light, which is then detected by the photoreceptor, generating a photocurrent at the output. This process enables "electrical-optical-electrical" conversion. While standard optocouplers are generally used for digital or switching signals, linear optocouplers can transmit continuous analog or current signals, expanding their application scope.
Optocouplers come in various types, such as dual in-line, tubular, and fiber optic configurations. They are classified based on internal circuitry, with examples including general-purpose, Darlington, high-speed, and fiber-based models. Their main advantages include unidirectional signal transmission, complete electrical isolation between input and output, strong noise immunity, long lifespan, and high efficiency. These features make them widely used in level shifting, signal isolation, switching circuits, long-distance communication, pulse amplification, solid-state relays, instrumentation, and computer interfaces.
Key technical parameters of optocouplers include the LED forward voltage (VF), forward current (IF), current transfer ratio (CTR), insulation resistance between input and output stages, and collector-emitter breakdown voltage (V(BR)CEO). For digital applications, parameters like rise time, fall time, delay time, and storage time are also important.
The CTR is a critical parameter, representing the percentage of DC output current (IC) relative to the DC input current (IF) when the output voltage is constant. For example, standard optocouplers like 4N35 have a CTR range of 20% to 300%, while the PC817 has a range of 80% to 160%. Darlington-type optocouplers, such as 4N30, can reach up to 5000%. This means that a smaller input current can produce the same output current, similar to the hFE of a transistor.
In contrast, linear optocouplers exhibit better linearity in their CTR-IF characteristics, making them suitable for analog signal transmission. Their AC current transfer ratio closely matches the DC value, ensuring a linear relationship between input and output, which is essential for precise analog applications.
When designing feedback circuits in switching power supplies, it's crucial to select a linear optocoupler with a CTR between 50% and 200%. A CTR below 50% may require excessive input current, increasing power consumption, while a CTR above 200% could cause false triggering during startup or load changes. Linear optocouplers like the CNY17-2 are ideal for precision voltage regulation, often paired with devices like the TL431C.
A practical example involves a multi-output power converter circuit with inputs ranging from 36V to 90V and outputs of +5V, +15V, and -15V. The circuit uses a TOP104Y monolithic switching IC, along with Schottky and ultra-fast recovery diodes for rectification. A linear optocoupler and TL431C form a feedback loop to regulate the +5V output precisely. Additional components like a transient voltage suppressor protect the power MOSFET from voltage spikes caused by transformer leakage inductance. This design achieves high efficiency and stable output performance.
Lead Acid Battery
Voltage: The voltage of the lead-acid battery is usually 12V or 24V and other standard voltage values.
Capacity: Capacity is an important indicator to measure the storage capacity of lead-acid batteries, usually expressed in ampere-hours (Ah). The capacity of different lead-acid batteries varies. Users can choose the appropriate capacity according to actual requirements.
Weight and size: The weight and size of lead-acid batteries vary by model and capacity. In general, the larger the capacity of the lead-acid battery, the greater the weight and size.
5. Development Trend
Performance improvement: With the continuous progress of technology, the performance of lead-acid batteries will be further improved, including improving energy density, extending service life, and reducing self-discharge rate.
Environmental requirements: With the enhancement of environmental awareness and the improvement of regulations, the environmental requirements for lead-acid batteries are becoming higher and higher. In the future, lead-acid batteries will pay more attention to the application of environmentally friendly materials and the recycling of waste batteries.
Intelligent development: Intelligence is one of the important development directions of the battery industry. In the future, lead-acid batteries will pay more attention to the application of intelligent technology, such as intelligent charging, intelligent monitoring and other functions will improve the efficiency and safety of the battery.
To sum up, Lead Acid Battery, as a traditional chemical battery, has the characteristics of low cost, mature technology and easy maintenance, and has been widely used in many fields. With the continuous progress of technology and the improvement of environmental protection requirements, the performance and environmental protection of lead-acid batteries will be further improved.
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