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CACD Group updated 2000.03.30 Author Janez Puhan |
Controlled Blocking OscillatorThe circuitMobile electronic equipment such as laptop computers and telecommunications equipment has to be powered from batteries. To achieve higher dc voltages, a series connection of several single cells is utilised. Due to the spread of charge capacities, the lifetime of a battery depends on the condition of the weakest cells. In applications where reliable operation is of primary interest only one single cell is permitted. Higher dc voltages then have to be stepped up by dc converters. A circuit used for this purpose is shown next in the form of a blocking oscillator. A low dc input voltage is chopped by a switching transistor, q1, the transformed and rectified again. The frequency of the regenerative switching action is determined by positive feedback, via l2, and ranges between 20 - 200kHz. To be independent of variations in battery voltage and load resistance, the dc voltage is stabilised by a "bang bang" control circuit. The reference element is a zener diode, d3. When conducting, q1 will be turned off until the dc output voltage has dropped down to nominal value.
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