FR-4 circuit plate board using military grade A material sheet, plate, and some stability tolerance parameters, A material behaved very tough, which is in the interests of a number of other relatively cheap price sheet. PCB board parameter elements are printed directly, without reference to a circuit diagram of the case can be soldered directly, very convenient. 1. The double-sided wiring, pads spray tin and tin increase Process pads, can withstand repeatedly desoldering, not easy to fall off. (Bending down refers to non-human conditions caused).  2. Since less likely to buckle, poor plate will change with time and the environment arising from bending. 3. Impedance more stable and reliable.Recommendation: input voltage (rectified smoothed voltage means rather than an AC voltage, AC input is rectified and filtered to 1.414 times, if the input voltage of 12V AC is rectified and filtered after 12 * 1.414 = 16.968V) at least higher than the output voltage is 3V, but do not be too high, too much pressure will only increase 317/337 power consumption, the chip heat, the output current can also be less, for example, as the input voltage is rectified and filtered voltage is 12V, output regulation to 5V, the regulator so that the pressure drop is above the chip 12-5 = 7V, if the time current Is 0.5A, then the power regulator tube is 0.5 * 7 = 3.5W, the greater the power, the more severe heat. Parameter: Board size approximately: length 62mm width 59mm high 30mm.  Input voltage: AC 5V- double dual AC 20V (only dual AC input).  Output DC: 1.3-25 V.  Current: 1 A.  Surge mode: linear buck regulator, the output voltage of the AC voltage is rectified and filtered after minus 3V. After such input dual 12V, the regulator rectifier filter voltage is above 12 * 1.414 = 16.968V, the output voltage can 16.968-3V = 13.968V Package Included: 3 x DIY LM317+LM337 Negative Dual Power Adjustable Kit