Supervisory circuit

Supervisory circuit

"Supervisory circuits" are combinations of semiconductor devices that detect and monitor voltage levels in power supplies, microprocessors, and other systems. They are protection circuits that monitor one or more system parameters. When parameter thresholds are exceeded or dangerous conditions exist, supervisory circuits react to protect the monitored system and correct the parameters. Supervisory circuits are known by a variety of names, including battery monitors, power supply monitors, supply supervisory circuits, and reset circuits.

Thermal Protection

Some supervisory circuits are used for thermal protection, and can consist of a temperature monitoring circuit, and a control circuit. The control circuit may either shutdown the circuitry it is protecting, throttle back the amount of power available in order to avoid over heating, or notify the system (software or use). These circuits may be quite complex, programmable and software run, or simple with predefined limits.cite web |url = http://www.maxim-ic.com/appnotes.cfm/an_pk/961 |title = Thermal Protection in Low-Cost Systems |accessdate = 2008-06-30 |publisher = Maxim Integrated Products ]

When a circuit is used to monitor the temperature of a specific component, it usually placed in a very close proximity. This is because the components used to detect the temperature, generally sense through the leads (pins) that are attached to the board. The farther the sensor is from the heat source, the less accurate the temperature is going to be.

Voltage Protection

Voltage protection consists of protecting the circuitry from either a case of supplying too much voltage to a load, or receiving too little voltage from a source. Either of these situations can have detrimental effects on the power circuitry of a system.cite web |url = http://focus.ti.com/lit/an/slva163/slva163.pdf |title = Overvoltage Protector for High-Voltage Loads |accessdate = 2008-06-30 |publisher = Texas Instruments ]

Two types of over voltage protection devices are currently used. These two types are clamping, which pass through voltages up to a certain level, and a foldback, which shunt voltage away from the load. The shunting creates a short circuit, which essentially takes the voltage away from the load circuitrycite web |url = http://www.tycoelectronics.com/documentation/whitepapers/pdf/eDigest-Circuit_Protection_Devices.pdf |title = Coordinated Circuit Protection Schemes Help Prevent Overvoltage and Overcurrent Damage |accessdate = 2008-06-30 |publisher = Tyco Electronics] . In certain applications this circuitry can reset itself after the dangerous condition has passed.

References

ee also

* [http://www.littelfuse.com/data/en/Product_Catalogs/Chapter1IntroductiontoCircuitProtection.pdf] From the Littelfuse Electronics Designer guide. PDF contains a good introduction to circuit protection.


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