PULSE APPLICATIONS
Looking at a common example, the pulse holdup in a handheld device GSM/GPRS transmission requires a current of approximately 2 A for the pulse duration. Due to battery and circuit impedance, the input voltage to the transmitter drops during the pulse (Fig. 3).
The battery voltage slowly drops as it is depleted of its charge and the transmitter can operate only above a certain input voltage. Therefore, to maximize the usage time before charging or replacing the battery, VM needs to be minimized. One solution is to connect a capacitor close to the transmitter, as this will provide the necessary pulse holdup characteristics
Apart from providing a technical solution, proton-polymer capacitors offer other advantages. For example, their wide voltage range lets them be used across the GSM chip (3.5 V), across the battery (4.5 V), or at the dc-dc converter (5.5 V). Also, their lowprofile, prismatic form factor enables them to fit into tight-quarter designs such as a PCMCIA, USB card, or LED camera flash.
Essentially, pulse holdup applications are defined as a system where an energy storage device, like a battery or fuel cell, supplies a low-power continuous load and also charges a capacitor that’s capable of short-term, high-power delivery on demand for peak load requirements. While many technologies can be used for the capacitor, as peak duty cycles increase such as in GPRS-8 to GPRS-10 topologies, then the applications suit the combined high-capacitance and low-ESR characteristics of proton-polymer pulse supercapacitors.
In fact, an application may have a mixedload requirement whereby a smaller bank of tantalums and a pulse supercapacitor can be used. Such pulse applications are everywhere, including combinations of electrical and electromechanical support. Examples range from digital cameras, ensuring capture is maintained while zoom and focus motors operate, to remote valve controls as in automated faucet to wireless remote valve activation.
The key is that proton-polymer pulse supercapacitors offer more battery options. With pulse support, standard non-rechargeable alkalines can be used in place of lithium- ion rechargeables, which can be useful for commodity electronics operated away from any convenient recharge facility.
Prior to pulse supercapacitors, the traditional approach was to use a high-power rechargeable battery, charged by a low-power primary cell. The pulse supercapacitor solution provides a number of benefits to the designer, including a substantially lower voltage drop for pulse durations up to 100 ms, a discharge current limited only by the ESR of the capacitor, a small form factor down to 1.8 mm, and a wider temperature range enabling a substantially lower voltage drop at cold temperatures in the ballpark of –20°C.
In essence, proton-polymer technology is based on an aqueous system where cells exhibit extremely repeatable voltage capabilities. This enables a wide range of voltage ratings to be manufactured from less than 2 V to support low-voltage power supplies up to 15 V.
The voltage repeatability means that these components are more than suitable to serialization, either as discrete capacitors in serialized banks or in volumetrically efficient modules. Also, no balancing resistors are needed for discrete parts and are optional with larger serial banks.