Customers that require miniature solutions with only functional isolation often choose isolated modules. These solutions have very bulky form factors, and typically do not provide high power efficiency or a low no-load input current. In addition, the output voltages of these modules are usually unregulated, having large VOUT variations due to line/load changes. But now, the LT8301, a simple-to-use no-opto isolated flyback converter can provide such customers a much more compact high-performance solution, using coupled inductors. With the micropower LT8301, high power efficiency and low no-load input current can be achieved. Meanwhile, the output voltage can be simply set by a resistor, and tightly regulated to the target value over a wide range of input voltage and load current.
The schematic in Figure 1 shows a miniature 5V isolated flyback converter using the LT8301, with a coupled inductor, L1, to provide functional isolation. The entire solution requires very few components, and the total size is about 13mm×7mm×3mm. The 5V output voltage is tightly regulated over a 2.7V to 16V input voltage range, with a peak power efficiency of 85%. To meet the 1mA minimum load requirement, a 5kΩ resistor should be added at VOUT, or a Zener diode should be used to clamp VOUT. In the case of VOUT being clamped by a 5.6V Zener diode, the no-load input current remains below 2mA over the entire input voltage range.