Application of Diodes in Power Supply Products and Auxiliary Analysis of Other Component Design

Application of Diodes in Power Supply Products and Auxiliary Analysis of Other Component Design

When designing power products, pay attention to the selection parameters of Schottky, fast recovery Diodes, and bridge stacks used in the scheme.

When designing a PCB, pay attention to the packaging size (heat dissipation space) of the actual product. For products with high output current, heat dissipation fins need to be installed to assist in heat dissipation. Especially for high-power and high current products, a fan (DC12V) needs to be added to assist in heat dissipation.

3. A certified power supply is required, and the input end needs to be equipped with a discharge , a safety capacitor, and a common mode inductor. When designing a PCB, the spacing between components and the first stage spacing between transformers is important.

4. Transformer surge current suppression protection scheme:

This solution is to use an NTC thermistor in series with the primary coil. When the switch is turned on, the thermistor has a high resistance value to suppress surge current. After a short period of time, due to self heating, the NTC thermistor's resistance value decreases to a very low value without affecting its normal operation.

5. The secondary rectification circuit of the transformer requires high efficiency and can choose full wave rectification. At this time, the transformer needs to add a winding. For half wave rectification circuits with limited space and the need for high current output, it is best to choose synchronous rectification because it can improve output efficiency without increasing the size of the heat sink.

6. In the rectification circuit, high-frequency and low resistance capacitors must be added for filtering after rectification (necessary for power supply products). A "π" type filtering circuit (transformer secondary) is composed of capacitors and inductors. If the output requires MEI, please add a common mode inductor. The rectifier diode in the fixed output circuit should not be too high (high voltage drop).

7. In power supply products, the design of transformers is particularly important, especially the control of transformer leakage inductance.

Summary of the impact of transformer leakage inductance on rectifier circuits:

① The voltage Ud at both ends of the rectifier output load decreases and there is a commutation overlap angle.

② The working status of rectifier circuits has increased.

③ The decrease in di/dt of the thyristor and the decrease in current change rate contribute to the safe conduction of the thyristor.

④ The voltage gap of the thyristor occurs during commutation, resulting in a positive du/dt. A positive voltage change rate can cause the thyristor to mislead, so an absorption circuit needs to be added.

⑤ Switching phases may cause voltage gaps in the power grid, causing interference to the power grid.

In the secondary power supply product, the coil turns of the auxiliary power supply winding can be increased by 2-3 turns based on the theoretical set number of turns, and then rectified by a fast recovery diode, and a series resistor is connected to power the main control chip.

For high-power power supplies (above 100W), especially LED driver power supplies with automatic dimming, to improve output efficiency and increase output stability, please add a PFC circuit.

10. When designing all power supplies, it is necessary to consider preventing short circuits and reverse connections, and to add a fuse in the circuit, preferably a self restoring fuse.

11. When using Schottky, fast recovery Diodes, and bridge stacks in the production of finished products, pay attention to temperature control during the production process and the humidity in the air.