Operating voltage: 2.5V~5.5V; Suitable for speaker: 4~8 ohm recommend to use for 4 ohm speaker speaker power: 2-8W; Powered by USB 5V port through PC or cellphone; This product can be also powered by lithium battery; High efficiency: 90%; With 4 ohm load and 5V power supplyit can provide 3W (left channel) + 3 W (right channel) output power; D class high power amplifier efficiency sound quality won't be affected by the high temperature and you don't need to use additional heat sink; With short circuit / over-current / over-temperature protection; Application: LCD TV monitors laptop portable speakers portable DVD players game consoles cellphones and hand-free phone.