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

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With the advancement of electronic technology, the complexity and application range of PCB (printed circuit board) have developed rapidly. Designers engaged in high-frequency PCBs must have a corresponding basic theoretical knowledge, and should also have rich experience in the production of high-frequency PCB. In other words, whether it is the drawing of the schematic or the design of the PCB, it should be considered from the high-frequency working environment in which it is located, in order to design an ideal PCB. This paper mainly studies the problems in high frequency PCB design based on Protel99SE from the manual layout and wiring of high frequency PCB.

1 layout design

Although Protel99SE has the function of automatic layout, it can not fully meet the working needs of high-frequency circuits. It is often necessary to rely on the designer's experience. According to the specific situation, the manual layout method is used to optimize the position of some components, and then combined with automatic layout. Complete the overall design of the PCB. The rationality of the layout directly affects the life, stability, EMC (electromagnetic compatibility) of the product, etc., must be from the overall layout of the circuit board, the feasibility of the wiring and the manufacturability of the PCB, mechanical structure, heat dissipation, EMI (electromagnetic Comprehensive considerations such as interference), reliability, and signal integrity.

Generally, the components in the fixed position related to the mechanical size are placed first, then the special and larger components are placed, and finally the small components are placed. At the same time, it is necessary to take into account the wiring requirements, the placement of high-frequency components should be as compact as possible, and the wiring of signal lines can be as short as possible, thereby reducing cross-interference of signal lines.

1.1 Placement of positioning inserts related to mechanical dimensions

Power sockets, switches, interfaces between PCBs, indicators, etc. are all positioning inserts related to mechanical dimensions. Usually, the interface between the power supply and the PCB is placed at the edge of the PCB and has a distance of 3mm to 5mm from the edge of the PCB; the indicator LED should be accurately placed as needed; the switch and some fine-tuning components, such as adjustable inductance, Adjustable resistors, etc. should be placed close to the edge of the PCB for easy adjustment and connection; components that need to be replaced frequently must be placed in a relatively small number of locations for easy replacement.

1.2 Placement of special components

High-power tubes, transformers, rectifiers and other heating devices generate more heat when operating at high frequencies. Therefore, ventilation and heat dissipation should be fully considered during layout. Place such components on the PCB where air is easily circulated. . High-power rectifiers and adjustment tubes should be equipped with heat sinks and away from the transformer. Electrolytic capacitors and other components that are afraid of heat should also be kept away from heat-generating devices, otherwise the electrolyte will be baked, causing its resistance to increase, performance to deteriorate, and affecting the stability of the circuit.

Components that are prone to failure, such as adjustment tubes, electrolytic capacitors, relays, etc., should also be considered for ease of maintenance when placed. For test points that often need to be measured, care should be taken to ensure that the test rods are easily accessible when arranging components.

Since the 50 Hz leakage magnetic field is generated inside the power supply device, it interferes with the low frequency amplifier when it is connected to some parts of the low frequency amplifier. Therefore, they must be isolated or shielded. The amplifier stages are preferably arranged in a straight line according to the schematic diagram. The advantage of this arrangement is that the ground current of each stage is closed at the current stage and does not affect the operation of other circuits. The input and output stages should be as far apart as possible to reduce parasitic coupling interference between them.

Considering the signal transmission relationship between the functional circuits of each unit, the low frequency circuit and the high frequency circuit should be separated, and the analog circuit and the digital circuit are separated. The integrated circuit should be placed in the center of the PCB so that the pins are easily wired to other devices.

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