The power supply shown in Figure 1 is implemented using a simple buck topology that allows for two output voltages without the need for a transformer. Typical applications include metering power supplies, where a 3.3 V supply is required for metrology and a 12 V supply is required to switch on and off relays or power a radio for remote meter reading. Resistor RF1 is a fusible fl ame proof type, which acts as a fuse in the event of a catastrophic failure and provides differential surge fi ltering. Diode D1 provides AC input rectifi cation while C1 and C2 Figure 1. 1.25 W Dual Output Supply Using LinkSwitch-TN. provide smoothing and, together with L1, act as a π-fi lter. EMI is further reduced by the integrated frequency jitter feature of the Link- Switch family of devices (see Figure 3). During the MOSFET off-time, capacitor C4 is charged to the output voltage via D3 (the voltage drops of D2 and D3 cancel). This voltage is used to provide feedback to U1 via the resistor divider formed by R1 and R2. The FB pin is sampled during each switching cycle. If the current that fl ows into the feedback pin of U1 is less than 49 μA, the subsequent cycle is enabled. During each enabled switching cycle, U1’s internal MOSFET is enabled, causing a linear ramp in current through L2 and C5. Once the internal current limit is reached, the MOSFET turns off, and the inductor current can freewheel via diode D2. Regulation is maintained by adjusting the ratio of enabled to disabled cycles.