Switching power supply is known for its efficiency. The adjustable voltage/current power supply is an interesting tool that can be used in many applications, such as lithium ion/battery chargers or power supplies.
The reason to build this switching power supply, need adjustable bench power supply. Linear topology for this power (2400W = 2.4 kW!) Would not be available, so a switch topology with two forward switches (half control bridge) was chosen. The switching power supply uses IGBT transistors and is controlled by a chip. The supply voltage is first passed through the EMI interference filter. It is then rectified with a bridge rectifier and smoothed with a capacitor. Because of the high capacity, there is a surge limiting circuit with relay contacts and R2 resistors. Relay coils and fans (via AT/ATX PC power supply) are powered by 12V, while resistor R1 is used to decompress them from 17V power supply. Select the R1 value so that the voltage on the relay coil and fan is 12V. The power circuit uses TNY267. It is similar to the power source described here. The R27 provides undervoltage protection for the power supply - it will not be turned on below 230V DC. The output frequency of the control circuit is 50kHz, with a duty cycle of 47 percent. It is powered by a Zener secondary, which reduces the power supply voltage to 5.6V (that is, to 11.4V) and moves the UVLO threshold from 7.9V (low) and 8.5V (high) to 13.5V and 14.1V. The chip then starts operating at 14.1 V and does not fall below 13.5 V, thus protecting the IGBT transistors from saturation.
