Double tube forward excitation small power supply design

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description:

This paper introduces a 30W power supply based on fixed frequency pulse width modulation control chip TL494, analyzes the structure of the circuit, and gives the specific circuit design and experimental waveform. The experimental prototype test shows that the circuit is practical and reliable, and the work is stable.

The forward conversion is widely used in small and medium power power conversion applications due to its simple topology and wide range of up/down steps. The output power of the forward converter is not limited by the energy storage of the transformer like the flyback converter, so the output power is larger than that of the flyback converter, but the voltage of the switching converter of the forward converter is high, twice the input voltage, sometimes Even more than twice the input voltage. Excessive switching transistor voltage is a key factor limiting the continued increase in forward converter capacity. The driver chip TL494 is a low-cost, high-drive capability, controllable dead time, and two error amplifiers for voltage and current feedback PI regulation when the load changes, which further enhances the stability of the power supply.

Dual tube forward converter circuit

The double-tube forward converter circuit is shown in Figure 1.

This main circuit topology has three advantages:

(1) Overcoming the shortcomings of high switching voltage stress in a single-ended forward converter.

(2) It is not necessary to adopt special flux reset technology to avoid complicated demagnetization winding design and reduce the volume of high frequency transformer, so that the circuit becomes simple, and there is no need to add RCD to perform complex magnetic clamping. The power supply is fed to improve efficiency.

(3) Compared with the full-bridge converter and the half-bridge converter, each bridge arm is composed of a diode and a switch tube in series, and there is no problem of straight-through of the bridge arm, and the reliability is high.

The grid module circuit is shown in the attached file. See the PDF document for details.