Battery Circuit DiagramsPower Supplies

Single-cell Power Supply Schematic Circuit Diagram

In the realm of contemporary electronic devices and microcontroller-based circuits, a stable power supply of either 5 V or 3.3 V is imperative. Maintaining the constancy of these voltages is crucial, especially in battery-powered devices. Traditionally, achieving this involved opting for a rechargeable battery with a voltage slightly higher than what the circuit demanded, coupled with a standard linear voltage regulator. However, this method proves to be inefficient in terms of both energy consumption and space utilization. To power a 5 V circuit, for instance, a minimum of six NiCd or NiMH cells would be necessary, leading to a wasteful scenario.

Modern electronic solutions provide innovative ways to address these challenges. One effective strategy involves the utilization of switching regulators, a technology that substantially curtails energy losses. By employing a regulator designed with a step-up topology, the number of cells required to power the circuit can be significantly reduced, leading to enhanced efficiency and conservation of valuable energy resources.

Single-cell Power Supply Schematic Circuit Diagram

Semiconductors Tailored for Portable Devices

Designing step-up converters for portable devices is made remarkably accessible due to the wide array of semiconductor devices crafted precisely for this purpose. An exemplary component, the Maxim MAX1708, exemplifies this convenience. Operating within an input voltage range of 0.7 V to 5 V, this integrated circuit, with a minimal setup involving external capacitors, resistors, a diode, and a coil, effortlessly produces a stable output of 3.3 V or 5 V.

Adjustable Output and Technical Features: Customizability and Specifications

With the incorporation of two additional resistors, the output voltage can be fine-tuned to any desired level between 2.5 V and 5.5 V. This versatile device, detailed comprehensively on the manufacturer’s website [1], possesses an internal reference and an integrated power switching MOSFET capable of handling currents up to 5 A. This feature facilitates scenarios like transforming 2 V at 5 A input into 5 V at 2 A output, enabling the creation of a 5 V regulated supply powered by just two NiCd or NiMH cells, while a single cell would yield around 1 A at 5 V.

Circuit Configuration and Component Selection: Precision in Design

The circuit design illustrated here caters to a 5 V output. Notably, a ‘soft start’ feature is enabled by the capacitor linked to pin 7 of the IC, and current limiting over 1 A is provided by R2. Removal of R2 allows for the maximum output current. Pins 1 and 2 offer control inputs for shutting down the device, while configuring it for a 3.3 V output involves a simple connection of pin 15 to ground. Component selection, especially for the coil and diode, is crucial and contingent on the desired current output. Employing a Schottky diode like SB140 is advisable for minimizing losses.

Limitations and Considerations: Voltage Discrepancies and Practical Constraints

A fundamental constraint of the step-up converter lies in the necessity for the input voltage to be lower than the desired output voltage. For instance, a 3.7 V lithium-polymer cell, even with a terminal voltage of 4.1 V when fully charged, cannot be utilized at the input to generate a 3.3 V output. This restriction arises due to the diode D1’s constant conduction under such conditions. However, generating a 5 V output from a lithium-polymer cell poses no challenges. Careful attention to these nuances ensures the effective utilization of step-up converters in practical applications.


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