Abstract: According to working condition of mine-used power supply in coal mine underground, novel intrinsically safe power supply with "ia" grade was designed. The power supply uses a fully enclosed AC-DC module to eliminate special flameproof enclosure, and has over-voltage protection circuit of dual redundancy and over-current protection circuit of three redundancy. The experimental results show there is no spark when the power supply load is short circuited under the conditions of no fault, one counting fault and two counting faults, which realizes intrinsic safety.