Battery load reduction solution using electric double layer capacitors

以智能手机、平板电脑为代表的便携式电子设备正以显著的速度发展着。便携式电子设备的多功能化、高性能化在不断进步，其便利性使我们使用便携式电子设备的机会增加，并增加了使用时间，但与此同时，其高性能化增加了电力的消耗。因此，电池被大容量化，并在便携式设备中占据了很大部分的体积和重量。但由于便携式电子设备被用来随身携带使用的机会很多，分量轻也就成为了其重要需求之一。因此，便携式电子设备中使用的电池要求具备大容量、体积小、重量轻的特征。

Power supply issues

It is not easy for batteries to have both large capacity and high load. Therefore, high load is handled by using software to disperse and control peak loads, but due to the development of applications such as smartphones and the diversification of user usage, it is difficult for power designers of the entire machine to predict the actual load status.

If batteries and electric double layer capacitors (EDLC) are used together, we can expect to achieve the aforementioned effect of reducing the high load state of the battery. In principle, the internal resistance of EDLC can be smaller than that of batteries, and the optimal design can be quickly responded to.

Features of Murata's Electric Double-Layer Capacitors

Murata's EDLC uses the most suitable electrode material and structure to achieve miniaturization, low resistance (tens of mΩ) and large capacity. Therefore, it is possible to release a large current of A command with low loss. In addition, compared with batteries, EDLC has little change in characteristics even in low temperature environments and can perform at the same level as at normal temperature.

Figure 1: ESR temperature characteristics

Figure 2: Discharge characteristics (5.5V, 350mF, 60mΩ product)

Battery load reduction effect using electric double-layer capacitors

The internal resistance of the battery is several hundred milliohms, which is several times that of Murata's EDLC. If only the large current of command A is released from the battery, the voltage will drop significantly and the loss will increase. In addition, if the voltage drops and exceeds the voltage lower limit of the protection circuit set by the battery, all operations will be forced to stop. This will cause the power supply to suddenly turn off (power off).

Here we list specific examples of using EDLC to reduce the load on the battery.

Figure 3 shows a circuit diagram that separates the internal resistance of the battery and EDLC and clearly marks them. In order for the EDLC to reduce the load on the battery, the EDLC and battery are connected in parallel.

The evaluation conditions are shown in Table 1. The loads set here are assumed to be peak loads of pulse-driven GSM and GPRS communications, high-output audio, small motors, etc.

Figure 3: Evaluation circuit diagram

Table 1 Evaluation conditions

The measurement results are shown in Figure 4.

Figure 4: Battery voltage and load current waveforms (left: without EDLC, right: with EDLC)

The load current of the battery is 1.9A without EDLC, but becomes 0.42A after connecting in parallel with EDLC. The drop voltage of the battery is also reduced from 0.38V without EDLC to 0.09V.

Therefore, after the EDLC and battery are connected in parallel, the load current and voltage fluctuations of the battery are suppressed, so that the electronic equipment can be in a stable working state. In particular, the low impedance of the internal resistance of Murata EDLC can support the load fluctuation at a high speed, especially for short-term pulse load current.

Murata Manufacturing's electric double-layer capacitor product line

Table 2 shows a list of Murata's EDLC products.

Table 2 EDLC product list (DME series)

Future Outlook

Portable electronic devices will enter the market with features of small size, light weight and multifunctionality. Since EDLC reduces the load on the battery, more convenient products can be produced.

Murata Manufacturing will continue to advance product development and contribute to the development of society by providing product solutions that meet current market needs, taking portable electronic devices as an opportunity.