I. The difference between non-isolated power supplies and isolated power supplies
An isolated power supply uses a transformer to reduce the 220V voltage to a lower voltage, and then rectifies it into a DC output for power supply. Because the primary coil of the transformer bears the 220V voltage, while the secondary coil only bears the low AC output voltage, and the primary and secondary coils are not directly connected, it is called an isolated power supply.
The difference between isolated and non-isolated voltage regulators is that the input and output circuits of an isolated voltage regulator are not grounded, while those of a non-isolated voltage regulator are grounded.
Generally, non-isolated inductors have primary and secondary inductor windings, while isolated inductors have only one inductor. Isolated inductors are used when high power and protection against grounding interference are required; non-isolated inductors are used when requirements are relatively simple and small in size are needed.
Isolated power supply: There is no direct electrical connection between the input circuit and the output circuit. There is a high impedance state of insulation between the input and output, and there is no current loop.
Non-isolated power supply: There is a direct current loop between the input and output, for example, there is a common ground between the input and output.
1. Security issues:
Isolated drives are safer but less efficient, while non-isolated drives are more efficient. We should choose between isolated and non-isolated drives based on the specific requirements of our application.
2. Regarding circuit structure:
Currently, most isolation solutions use AC/DC flyback circuits, resulting in complex and costly circuitry. Non-isolated solutions are typically DC/DC boost or buck circuits, which are relatively simpler and less expensive.
II. What are the application designs for non-isolated power supplies?
1) 220V to 5V step-down circuit: Input 12~380Vac, output 5V/500mA non-isolated power supply
The output is a non-isolated 5 V/500 mA power supply, with an input power range of 12-380 Vac. It is commonly used in household appliances (rice cookers, washing machines, and other white goods). This circuit is also suitable for other non-isolated power supply applications, such as LED drivers, smart meters, heaters, auxiliary power supplies, and industrial control.
The power supply system features various protections, including over-temperature protection (OTP), VCC undervoltage lockout (UVLO), overload protection (OLP), and short-circuit protection (SCP). Circuit characteristics: noiseless and low heat generation.
The input stage of the 220V to 5V step-down circuit consists of a fuse resistor RF1, a surge protector varistor RV1, a rectifier bridge rectifier D1, EMI filter capacitors C4 and C5, and a filter inductor L2. The fuse resistor RF1 is a flame-retardant fusible wire-wound resistor that serves multiple functions: a) limiting the surge current of the bridge rectifier D1 to a safe range; b) attenuating differential-mode noise; and c) acting as an input fuse in case of a short-circuit fault in any other component (the circuit must be safely open in case of a component failure, without producing any smoke, fire, or overheating). The varistor RV1 provides surge protection, improving system reliability. The power processing stage consists of a wide-voltage, high-efficiency power supply chip XD308H, a freewheeling diode D2, an output inductor L1, and an output capacitor C3.
2) 220V to 12V step-down circuit: Input 32~380Vac, Output 12V/500mA non-isolated power supply
The output is a non-isolated 12 V/500 mA power supply, with an input power range of 32-380 Vac. It is commonly used in household appliances (rice cookers, washing machines, and other white goods). This circuit is also suitable for other non-isolated power supply applications, such as LED drivers, smart meters, heaters, auxiliary power supplies, and industrial control.
The power supply system features various protections, including over-temperature protection (OTP), VCC undervoltage lockout (UVLO), overload protection (OLP), and short-circuit protection (SCP). Circuit characteristics: noiseless and low heat generation.
The input stage of the 220V to 12V step-down circuit consists of a fuse resistor RF1, a surge protector varistor RV1, a rectifier bridge rectifier D1, EMI filter capacitors C4 and C5, and a filter inductor L2. The fuse resistor RF1 is a flame-retardant fusible wire-wound resistor that serves multiple functions: a) limiting the surge current of the bridge rectifier D1 to a safe range; b) attenuating differential-mode noise; and c) acting as an input fuse in case of a short-circuit fault in any other component (the circuit must be safely open in case of a component failure, without producing any smoke, fire, or overheating/lighting). The varistor RV1 provides surge protection, improving system reliability. The power processing stage consists of a wide-voltage, high-efficiency power supply chip XD308H, a freewheeling diode D2, an output inductor L1, and an output capacitor C3.
