Protel 99 SE high frequency PCB design research - Power Circuits - Circuit Diagram

Probe for domestic high-frequency needles, such as JKT-50L high-frequency needle with 3 probes.

Full range of MOS power ICs.

Shunluo high-frequency inductors, parallel stack inductors, and custom-wound inductors, with authorized agency representation.

Industrial router crystals measuring 3.2x2.5mm, model 3225, 26M (26.000MHz), with capacitance options of 12PF and temperature stabilities of 10PPM, 20PPM, and 30PPM.

With the rapid development of electronic technology, printed circuit boards (PCBs) have become increasingly complex and widely applied. Designers working on high-frequency PCBs must possess a strong theoretical foundation and practical experience. Both the schematic design and PCB layout must consider the high-frequency working environment to achieve optimal functionality. This article focuses on the challenges of high-frequency PCB design using Protel99SE, particularly emphasizing manual layout and wiring techniques.

1. Layout Design

While Protel99SE offers an auto-layout feature, it cannot always meet the specific demands of high-frequency circuits. Manual intervention by experienced designers is often necessary. After optimizing the positions of critical components manually, the remaining layout can be completed using automated tools. A well-thought-out layout impacts the lifespan, stability, and electromagnetic compatibility (EMC) of the final product. Factors like manufacturability, mechanical structure, thermal management, and signal integrity must all be considered holistically.

Typically, components tied to mechanical dimensions, such as power sockets, switches, and connectors, are placed first. Larger and specialized components follow, with smaller ones placed last. Wiring constraints should guide the process, ensuring high-frequency components are tightly packed and signal paths are as short as possible to minimize cross-talk.

1.1 Placement of Positioning Inserts Related to Mechanical Dimensions

Interfaces like power supply connectors, switches, and LEDs should be positioned strategically. Power supply connectors are typically placed along the edge of the PCB, about 3mm to 5mm from the board's edge. Indicators should be aligned precisely as required. Fine-tuning components like adjustable inductors and resistors should be positioned near the board’s edge for easy access. Frequently-replaced components should be placed in convenient locations for maintenance purposes.

1.2 Placement of Special Components

High-power devices like transformers and rectifiers generate significant heat at high frequencies. Proper ventilation and heat dissipation are essential during layout. These components should be placed in areas where airflow is optimal. High-power rectifiers and regulators should be mounted with heat sinks and kept away from transformers. Heat-sensitive components like electrolytic capacitors should also be distanced from heat sources to avoid performance degradation.

Components prone to failure, such as electrolytic capacitors and relays, should be placed for easy maintenance. Test points should be accessible for measurement purposes. To prevent interference, low-frequency amplifiers and power supplies should be isolated or shielded. Amplifier stages should ideally follow the schematic layout, minimizing ground current interaction between stages. Input and output stages should be spaced apart to reduce parasitic coupling.

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