Current Limiting

Written by Kevin Tavolaro
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Current limiting is a process in electrical power transmission that reduces the load voltage to zero, yet allows the load current to reach a maximum value. When properly applied, this process results in less dissipation within the transmitter, especially under shortened conditions.

By curtailing the load voltage, yet allowing for the transmission of power, this process acts as a protective measure to the electrical device. In shortened conditions, diodes and transistors are likely to blow out faster than a fuse. Current limits secure these components by reducing their exposure to excess heat. However, the process itself maintains efficiency and reliability by curbing dissipation within the same device.

Current Limiting and Heat

Many power supplies are now equipped with built-in current limiting. In these devices, current limiting can be employed as a fail-safe measure, in order to keep the device itself from damage. Because an AC transmission is more difficult to regulate than the one-way flow of DC, current limiting can be utilized to alter the flow and capacitance if the temperature suddenly rises too high too quickly. In this event, concerns over dissipation come second to protecting the device's components from the effects of overheating. Some power supplies also include another measure, intended for extreme situations, called thermal shutdown. Thermal shutdown halts the transmission of energy in the event of a sudden escalation in temperature.

The process is regulated through the printed circuit board. A current limit circuit is affixed to the board in order to monitor the electrical transmissions that pass through it. A secondary current limit circuit is often attached as well. This component protects the active power stage from output current overloads, as well as short circuits. This is all regulated by the transmission of feedback voltage, which informs the circuit of the current atmosphere inside the device.

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