Flyback is the most common circuit topology to build galvanically isolated AC to DC or DC to DC converters. Flyback circuit is cheap and relatively easy to manufacture, therefore nowadays the majority of home or industrial appliances are powered using AC to DC Flyback converters. In general, a Flyback converter is suitable for low-power applications, mostly below 100W.
In this article/video, I designed a cheap AC-to-DC flyback converter using a DK124 IC that can deliver up to 18W continuously. I calculated the transformer to handle 12V at the output which can be easily modified to reach other output voltages as well. The DK124 chip does not need any auxiliary winding or even an external startup resistor. The 220V Mains input has been protected using a MOV, an NTC, and a Fuse. The PCB board is single-layer and all components are through-hole.
To design the schematic and PCB, I used Altium Designer 22. The fast component search engine (octopart) allowed me to quickly consider components’ information and also generate the BOM. To get high-quality fabricated boards, I sent the Gerber files to PCBWay. To test the power supply, I used Siglent an SDL1020X-E DC Load, an SDM3045X Multimeter, and an SDS1104X-E/SDS2102X Plus oscilloscope.
P1 is a terminal connector for 220V-AC. F1 is a 500mA fuse to protect the board, PCB tracks, and wiring against unpredicted malfunction or short-circuit. R2 is a 10D561 varistor [2] to provide high-voltage clamping and surge protection. C2 is a 100nF X2 capacitor to reduce the noise. T1 is a common-mode choke for high-frequency noise suppression and waveform distortion prevention. BR1 is a bridge rectifier and C3 reduces the ripple of the rectified voltage.
R3, C4, and D1 build a snubber circuit to suppress transient spikes of the transformer. The snubber protects the switching Mosfet and reduces the EMI as well (Mosfet was embedded inside the DK124). IC1 is the flyback controller chip. According to the Dk124 datasheet: “The DK124 IC is specially designed for off-line switch mode power supply, maximum power is 24W. Different from the PWM controller and external power-separated MOS combination design, the PWM controller, 700V power transistor, and high voltage starting circuit are integrated into his DK124 IC, to save external circuits, component use, and cost. Also, the size and weight of the product are reduced. It is especially suitable for price-sensitive flyback switch mode power supply.”
C10 and C11 capacitors are used to reduce the noise. OP1 is the PC817 [3] optocoupler to provide an isolated feedback path and balance the output voltage. D1 is a Schottky diode to rectify the voltage of the secondary winding of the transformer (T2). C5 and C6 are used to reduce the voltage ripple. L1, C7, and C8 build an LC filter to reduce the noise and ripple. D3 is a 3mm LED to indicate a proper output voltage and R5 limits the D3 current. D3 also plays a role of a small dummy load to help to stabilize the output. R9 potentiometer is used to adjust the output voltage and fix it on 12.0V. Reg1 is the TL431 [4] shunt regulator.
As it is clear, IC1 (DK124) does not need any external supply (an axillary transformer winding) or even a resistor for the startup phase.
PCB Layout
Figure 2 shows the PCB layout of the switching power supply. It’s a single-layer PCB board. I used Altium designer to draw the PCB. Figure 3 shows the assembly drawings. As you see, I created two board cut-out areas (isolation gaps) to follow the IPC rules of high-voltage and creepage.
Flyback is the most common circuit topology to build galvanically isolated AC to DC or DC to DC converters. Flyback circuit is cheap and relatively easy to manufacture, therefore nowadays the majority of home or industrial appliances are powered using AC to DC Flyback converters. In general, a Flyback converter is suitable for low-power applications, mostly below 100W.
In this article/video, I designed a cheap AC-to-DC flyback converter using a DK124 IC that can deliver up to 18W continuously. I calculated the transformer to handle 12V at the output which can be easily modified to reach other output voltages as well. The DK124 chip does not need any auxiliary winding or even an external startup resistor. The 220V Mains input has been protected using a MOV, an NTC, and a Fuse. The PCB board is single-layer and all components are through-hole.
To design the schematic and PCB, I used Altium Designer 22. The fast component search engine (octopart) allowed me to quickly consider components’ information and also generate the BOM. To get high-quality fabricated boards, I sent the Gerber files to PCBWay. To test the power supply, I used Siglent an SDL1020X-E DC Load, an SDM3045X Multimeter, and an SDS1104X-E/SDS2102X Plus oscilloscope.
P1 is a terminal connector for 220V-AC. F1 is a 500mA fuse to protect the board, PCB tracks, and wiring against unpredicted malfunction or short-circuit. R2 is a 10D561 varistor [2] to provide high-voltage clamping and surge protection. C2 is a 100nF X2 capacitor to reduce the noise. T1 is a common-mode choke for high-frequency noise suppression and waveform distortion prevention. BR1 is a bridge rectifier and C3 reduces the ripple of the rectified voltage.
R3, C4, and D1 build a snubber circuit to suppress transient spikes of the transformer. The snubber protects the switching Mosfet and reduces the EMI as well (Mosfet was embedded inside the DK124). IC1 is the flyback controller chip. According to the Dk124 datasheet: “The DK124 IC is specially designed for off-line switch mode power supply, maximum power is 24W. Different from the PWM controller and external power-separated MOS combination design, the PWM controller, 700V power transistor, and high voltage starting circuit are integrated into his DK124 IC, to save external circuits, component use, and cost. Also, the size and weight of the product are reduced. It is especially suitable for price-sensitive flyback switch mode power supply.”
C10 and C11 capacitors are used to reduce the noise. OP1 is the PC817 [3] optocoupler to provide an isolated feedback path and balance the output voltage. D1 is a Schottky diode to rectify the voltage of the secondary winding of the transformer (T2). C5 and C6 are used to reduce the voltage ripple. L1, C7, and C8 build an LC filter to reduce the noise and ripple. D3 is a 3mm LED to indicate a proper output voltage and R5 limits the D3 current. D3 also plays a role of a small dummy load to help to stabilize the output. R9 potentiometer is used to adjust the output voltage and fix it on 12.0V. Reg1 is the TL431 [4] shunt regulator.
As it is clear, IC1 (DK124) does not need any external supply (an axillary transformer winding) or even a resistor for the startup phase.
PCB Layout
Figure 2 shows the PCB layout of the switching power supply. It’s a single-layer PCB board. I used Altium designer to draw the PCB. Figure 3 shows the assembly drawings. As you see, I created two board cut-out areas (isolation gaps) to follow the IPC rules of high-voltage and creepage.
No comments:
Post a Comment