Electronics Weekly Electronics Design & Components Tech News
Called the SABMBOVP2xx family of products, they are small PCBs based around the firm’s ALD9100xx ICs, with added current-boosting output fets.
ALD9100xx ICs (circuit below) include two voltage-dependant current sinks that conduct heavily above a certain voltage – acting as voltage clamps.
Rather than a typical reference-op-amp-power-transistor circuit, each of the two devices in the chip is essentially an enhancement-mode fet where the gate can be connected to its drain, making the chip essentially a pair of two-terminal devices – see diagram – the gate-to-drain connections are actually made externally to the chip .
Threashold voltages are precision-trimmed to give the required V-I characteristic.
Taking the ALD910023 chip as an example:
- 2.2V 0.1µA
- 2.3V 1µA (this is the nominal voltage)
- 2.4V ~10µA
- 2.52V 100µA
ALD sees this soft characteristic as well suited to automatically balancing series supercaps. They represent “an effective variable resistor that varies in value exponentially with Vin. This Vin, when connected across each supercapacitor in a series, balances each supercapacitor to within
its voltage and current limits”, according to the firm. “When an ALD910023 is connected across a supercapacitor that charges to less than 2.10V, it would dissipate essentially no power.”
Maximum allowable current through the chip is 80mA, and maximum allowable voltage across both capacitors together is 15V.
However, once the current-boosting output fets are added on the SABMBOVP2xx boards, gain also increases, creating a sharper characteristic that the firm sees as suited to balancing larger supercaps.
Taking a particular example (SABMBOVP225):
- 2.30V 0.01µA.
- ~2.40V 0.07µA
- 2.5V 1mA
- 2.53V ~100mA
“Hence at any voltage less than 2.4V, there is essentially no power dissipation or any energy draw from the supercapacitors. Above the 2.5V threshold level, current increases sharply and
steeply, to near vertical. Current at 2.53V is 1,400,000 times higher than at 2.4V,” said the firm.
The standard SABMBOVP225 board is designed to limit current to ~100mA (at >2.53V). Connecting a pair of 24Ω 1W resistors to the board increases this to ~200mA.
Board size is ~15.2 x 40.1 mm and operation is over -40°C to +85°C. Construction is on RoHS-compliant FR4.
Applications are foreseen in automotive, transportation, automation, data centres and power grids – even at high voltages, as they are “ideally suited for balancing large supercapacitors that are stacked in a series, from two to hundreds of cells with values of 0.1F to 3,000F and beyond”.
