Increased battery life. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Increased battery life. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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Many battery powered devices require that the output voltage be maintained at a constant level, regardless of whether the battery voltage is below or above this level. This requirement is easily met when the battery voltage exceeds 15 V [1]. But for low-voltage batteries, the solution to the problem can be very difficult. By providing a floating battery negative terminal that is normally grounded when powered positively, it is possible to simplify the construction of a positive diode reverse converter.

The voltage of the battery supplying the proposed device can be in the range from 3 to 30 V (see figure). The switching regulator model LT 1072 controls the transfer of power from the input to the output. The output Vsw of the regulator is the collector of an npn transistor connected in a common emitter circuit; thus, the flow of current into the regulator is ensured at a low potential at this pin. The generation frequency of the circuit, equal to 40 kHz, is determined by the built-in generator. When the key on this transistor is turned on, the battery voltage is applied to the inductor L1 and energy is stored in its core. However, when the switch is turned off, current flow through the LT 1072 stops. As current continues to flow through the inductor, diode D1 becomes forward biased, allowing the energy stored in the inductor to be transferred to the output.

(click to enlarge)

Output voltage regulation is achieved by applying a voltage of up to 1,25 V to the control input (Vfb). The IC is controlled relative to the common output; thus, level shifting should be done from the 5V output. Transistor Q1 serves this purpose, providing an output voltage temperature drift of only -2 mV/°C. This value is usually sufficient for logic power supplies, but can be corrected by an additional carefully selected diode-resistor circuit. The minimum required load current is in any case 1 mA. If more current is needed, the LT 1072 regulator can be replaced with an LT 1070 or LT 1071 IC.

Literature

William, J. and Huffman B. "Some thoughts on DC-DC converters", Linear Technology Corp., Application Note 29, Feb. 1989.

Author: Brian Huffman; Publication: N. Bolshakov, rf.atnn.ru

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