Single Capacitor Powers Audio Mixer

Micropower and low-voltage op amps allow you to build high-performance analog-signal processors that require no batteries or wall transformers. Instead, you can use a capacitor as a power source. The circuit in Figure 1 shows an analog mixer designed for audio editing that you can connect between a camcorder and a VCR. A capacitor, such as a Super
Single Capacitor Powers Audio Mixer - schematic

cap or Dynacap, exclusively powers the circuit. These capacitors have values from 0. 047 to 1. 5F and maximum operating voltages of either 5. 5 or 11V. The capacitor in Figure 1 is approximately 1. 5 in. wide and 1 in. high, which is a reasonable size for a portable design. Using a capacitor as a voltage supply has many potential advantages vs regular disposable or rechargeable batteries. The Supercap has a typical charge time of 10 to 20 sec. To charge the capacitor, you can use any regular wall transformer unit with a filtered or unfiltered, regulated or unregulated, 5 to 10V-dc output. There is no risk of overcharging the capacitor and therefore no need for accurate charge-current and time monitoring. Capacitor charge/discharge cycles are practically infinite. These voltage supplies have no disposable parts and no leaks. When using a capacitor, there is no chemical contamination or oxidation of electrodes. The capacitor can withstand short circuits for an unlimited time and may be discharged to any level without damage. You can easily connect capacitors in parallel without side effects, such as bias current between paralleled batteries. The analog-signal processor in Figure 1 centers on the rail-to-rail, low-voltage, micropower quad LMC6574 op amp. This op amp`s specifications make it suitable for this portable-audio application. The op amp can operate from supply voltages as low as 2. 7V with guaranteed rail-to-rail...

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