Power supplies

Power supply technology has been in existence since the beginning of the electronic world. All electronic circuits need to be powered from a reliable direct current (DC) source and such power source must be generated from an everlasting source of alternating current (AC) power. Switching power converters are common systems which typically have an input terminal for receiving an input voltage, and an output terminal which supplies current to a load. The output terminal provides a substantially fixed voltage independent of the magnitude of the input voltage or the current provided to a load. Most of the traditional power supply devices are linear power supply devices, which are usually used for an instrument providing a constant voltage and a constant current, which has a low ripple noise, a low EMI, a good modulation, and an easy-to-control features. The linear power supply requires a transformer to step-down or step-up the AC voltage at the input frequency of 50/60/400 Hz. The rectifier circuit rectifies the AC voltage to desired pulsating DC voltage and the output filter, together with the voltage regulator circuit, regulates the intermediate voltage to the desired DC voltage. Power electronic circuits are used to control and condition electric power. For instance, power electronic circuits may be used to convert a direct current into an alternating current, to change voltage or current magnitude, or to change the frequency of an alternating current. Power supplies are required in the operation of many electrical devices. There are a wide variety of power supplies including batteries, fuel cells, electro-mechanical generators, alternating current to direct current supplies, inverters, and alternating current supplies, among many others. Batteries are a type of electrochemical cell containing a pair of electrodes and an electrolyte disposed between the electrodes. Batteries can be grouped into a primary type and a secondary type. The primary type comprises disposable batteries, and the secondary type comprises rechargeable batteries. The rechargeable batteries can further be grouped into four types: NiMH (nickel metal hydride), NiCd (nickel cadmium), Li-Ion (Lithium Ion), and sealed lead acid batteries. Rechargeable batteries have gained wide acceptance and usage as power sources for portable appliances. Mobile phones, digital cameras, camcorders, laptop computers, and personal digital assistants are just a few of the many appliances now using rechargeable battery technology. Battery chargers are often provided as either internal or external devices to be used to recharge these batteries. Generally, the rechargeable battery is charged with a transformer that converts current from a conventional electrical outlet or automobile lighter into direct current suitable for charging the battery. Rechargeable batteries are provided with a variety of protective functions for preventing damage to the battery caused by abnormal use such as overcharging, overdischarging, short-circuiting between the positive and negative electrodes. An uninterruptible power supply (UPS) is a type of power supply used to power and protect an electrical load that is sensitive to fluctuations in or the absence of electrical power. A UPS typically comprises a rectifier, inverter, and battery charger.