Nowadays, large capacitors are often used to provide a good range of back up to various equipments used in different applications. This can be illustrated explicitly by taking a daily life example of modern electric or hybrid cars. In addition to the traditional lead acid battery, such types of cars use large capacitors as a back up source and the capacitors have the value of 40F or more.
In the car, this capacitor is mounted under the rear seat and promises you to provide an extra 10 to 15 minutes of back up so that you can drive up to the next charging station or gas station. Lead acid battery discharge down to only 8V whereas capacitor can discharge to 0V. So, for this application a current sensing amplifier is required which can measure inputs to 0V. Because most high side current sense amplifiers operate over a limited range of common mode input and supply voltages, so this problem is solved by connecting a Charge Pump in the circuit.
Block Diagram using a Charge Pump to extend the common mode input limit of Current Sensing Amplifier up to 0V
The charge pump and the current sensing amplifier are powered from the same input supply and the output of the charge pump acts as a negative supply voltage at the ground pin of current sensing amplifier IC. A supply of current from the amplifier to the charge pump act as a small load current which prevents overloading and voltage drooping at its output.
The most suitable charge pump series for this kind of application is XC6351A. |
