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# The funcition of super capacitor

May 28,2016

Characteristics of the high power pulse application: instantaneous large current flows to load;Keep application characteristics of instantaneous power: demand continued to provide power to the load, generally for a few seconds or minutes duration.Keep a typical application of instantaneous power: when the power is reset disk drive head.Different application requirements for the parameters of the super capacitor is also different.High power pulse application is the use of super capacitor small internal resistance (R), while the instantaneous power kept is the use of electrostatic capacity of super large capacitance (C).

The following provides two formulas and examples of application:
Nominal capacity C (F) : super capacitor;
The nominal resistance R (Ohms) : super capacitor;
The ESR (Ohms) : 1 kz equivalent series resistance;
Uwork (V) : during normal working voltage in the circuit;
Umin (V) : the minimum voltage devices work;
T (s) : the time to maintain the requirements in the circuit or the pulse duration pulse application;
Udrop (V) : at the end of the discharge or large current pulse, the total voltage drop.
Instantaneous power applications
Super approximate calculation formula of capacitance, according to the formula, maintaining the needed energy = super capacitor to reduce energy.
The energy required to keep the period = 1/2 I (Uwork Umin +) t;
Super capacitor energy = 1/2 (Uwork2 - Umin2) c,

Thus, available capacity (ignore the pressure drop caused by the IR) = (Uwork Umin +) t/C (Uwork2 - Umin2)

Example:
Assuming that tape drive the working voltage of 5 v, safety working voltage 3 v.If dc motor 0.5 A keep 2 seconds (safe), so, according to the formula can get the capacity of at least 0.5 F.
Because 5 v voltage than the monomer nominal working voltage of capacitor.Therefore, can be two capacitor in series.As two of the same capacitor in series, the voltage of each is the nominal voltage of 2.5 V.
If we choose the nominal capacity is 1 F capacitor, two series of 0.5 F.Considering the capacitor - 20% of the capacity of the deviation, this choice does not provide enough margin.Can choose the nominal capacity is 1.5 F capacitor, can provide 1.5 F / 2 = 0.75 F.Consider deviation - 20% of capacity, the minimum 1.2 F / 2 = 0.6 F.The super capacitor provides adequate safety allowance.After the big electric current pulse, tape drive into small current work mode, with super capacitor residual energy.