MAXREFDES1151: Supercapacitor charger and dv/dt compensation

Supercapacitors have unique advantages in modern electronic products. In practical applications, a major consideration in supercapacitor-related design is dv/dt compensation. When a large transient current occurs in the supercapacitor load, the internal resistance of the battery produces a large voltage drop on the battery. For example, when connecting a 10A load to a 10V battery with an internal resistance of 0.2Ω, the voltage drop across the internal resistance is 2V. As the current increases, the battery's output voltage decreases, which we call dv/dt. In order to provide sufficient system voltage, designers will choose to use ultra-large-capacity batteries. Another wise choice is to use supercapacitors to compensate for dv/dt voltage drops. The supercapacitors provide additional energy to support transient large load power supply and prevent battery voltage drops. This design allows the use of smaller batteries and supports transient heavy loads, ensuring battery operating life.

The design consists of two parts. The first part uses MAX406 to charge the supercapacitor with 1A constant current; the second part uses MAX1725 and MAX985 to slow down the change of dv/dt.

Key Features

• Input voltage range: 5V – 10V

• Charging current 1A

• Maximum voltage drop: 5%

• Maximum transient load supported: 5A, duration 500ms

• Battery internal resistance: 1Ω

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Design, build and test

This document introduces the reference design shown in Figure 1 and provides detailed technical guidance for designing supercapacitor charging and dv/dt compensation circuits. The circuit has been built and tested, please refer to this document for details.

design resources