Supercap Chgr
Controls charging current and the final capacitor-bank voltage. A bank rated for several volts may contain multiple lower-voltage cells in series: the bank voltage must not be applied to each cell. Cell balancing is a separate design requirement and is not included in every charger.
A charger regulates current while the capacitor voltage rises, then regulates voltage near the target. The exact transition, minimum output voltage, thermal limits and termination behaviour depend on the IC. Series banks also need a suitable balancing arrangement to keep every cell within its own rating despite capacitance and leakage differences.
In plain terms
Like a railway tanker filling station — a freight car (supercap) has enormous tank volume and would split a hose if filled fast, so the station meters the flow and stops at the safe fill line.
Why designers use it
- Controls charging inrush instead of connecting an empty capacitor bank directly across a stiff supply.
- Regulates voltage to a value selected from the exact capacitor and bank specifications.
- Can support backup-power and energy-buffer applications when stored energy, losses and load demand have been calculated.
- Dedicated chargers and suitably configured battery chargers offer different trade-offs; TI documents several examples rather than one universal circuit.
Best for
- Backup power
- Energy storage
- Pulse loads
Key specifications
- Charge voltage: Match the exact bank and each cell's recommended rating
- Charge current: Check capacitor, charger, input supply and thermal limits
- Balancing: Required design assessment for series cells; not automatic in every charger
- Backup duration: Calculate usable energy, voltage window, load and conversion losses
When not to use it
- For a single small (<1 F) supercap charged through a series resistor — discrete is simpler.
- Where the source is already current-limited (e.g., a USB port at 500 mA) — a current-limit-only resistor is enough.
Common mistakes
- Confusing a series bank's voltage with the allowed voltage of each cell.
- Assuming the charger contains cell balancing without checking its features and schematic.
- Copying a battery-charger configuration without checking its precharge, termination and minimum-output behaviour for capacitors.
- Ignoring charging heat, current limits, capacitor leakage or the load current during charging.
Where you will find it
- TI's application note demonstrates charging a 10 F capacitor arrangement to 5 V with a BQ25798 and TPS25221. Those demonstration values describe that arrangement, not permission to charge an individual low-voltage cell to 5 V.
A short history
Supercapacitor charging can use dedicated controllers or carefully configured battery chargers. TI's examples show why startup at low capacitor voltage, current regulation and charge termination must all be considered. Eaton's guidance separately explains cell-voltage imbalance and balancing in series banks.
Good to know
- A suitable total bank voltage does not prove that every cell is at a suitable voltage.
- A charger and a cell balancer solve related but different problems.