Battery Technology - May 2021 - 4

Charge Control Methods for

Supercapacitors

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ircuit designs exploiting the increased energy storage provided
by supercapacitors require more careful consideration of the increased power handling than that of
batteries when charging these devices.
The unique composition of electrochemical double-layer capacitors (EDLC) inherently allows them to withstand large currents. Table 1 is a brief list of AVX
cy lindrical (SCC) and series-connected
module (SCM) SuperCapacitors, displaying peak current supply and sink current
capability. These maximum specifications
will typically exceed current capability of
charge sources and lead to failures
within the power supply system.
Supercapacitors have low
equivalent series resistance (ESR), causing
an uncharged
superca-

pacitor to appear as a dead short. This
will instantaneously draw maximum current from the source in an attempt to
charge up to its rated capacitance [I = C x
(dV/dt)]. Typically, this charge current
greatly eclipses what the power source is
able to supply. In many instances, the
amount of current draw is so much more
than what the power supply can handle
that it will drive the power source or system into permanent failure or at least a
transient upset.
To demonstrate this, compare the current draw by a supercapacitor to a transient containing hundreds or thousands of
amps, causing significant voltage drop
across sensitive circuits and resulting in
bit error on high-speed transceivers, system shutdown, or software reset. In an
effort to mitigate this problem, many
charge limiting circuits exist but a
high-level comparison of passive
and active control methods can
help determine which topology to implement.

AVX Capacitor
Series

MAX
Capacitance

Voltage
Rating

MAX Peak
Current

SSC

3000 F

2.7 V

2165 A

SCM

15 F

5.4 V

23.5 A

16V SCM

500 F

16 V

1900 A

48V SCM

165 F

48 V

2165 A

Table 1. Supercapacitor capability to sink and supply current.

Battery Technology, May 2021

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Battery Technology - May 2021

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