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Printed circuit board


A printed circuit board (PCB) mechanically supports and electrically connects electronic components using conductive tracks, pads and other features etched from copper sheets laminated onto a non-conductive substrate. Components (e.g. capacitors, resistors or active devices) are generally soldered on the PCB. Advanced PCBs may contain components embedded in the substrate.
PCBs can be single sided (one copper layer), double sided (two copper layers) or multi-layer (outer and inner layers). Conductors on different layers are connected with vias. Multi-layer PCBs allow for much higher component density.
FR-4 glass epoxy is the primary insulating substrate. A basic building block of the PCB is an FR-4 panel with a thin layer of copper foillaminated to one or both sides. In multi-layer boards multiple layers of material are laminated together.
Printed circuit boards are used in all but the simplest electronic products. Alternatives to PCBs include wire wrap and point-to-point construction. PCBs require the additional design effort to lay out the circuit, but manufacturing and assembly can be automated. Manufacturing circuits with PCBs is cheaper and faster than with other wiring methods as components are mounted and wired with one single part.
A minimal PCB with a single component used for easier prototyping is called a breakout board.
When the board has no embedded components it is more correctly called a printed wiring board (PWB) or etched wiring board. However, the term printed wiring board has fallen into disuse. A PCB populated with electronic components is called a printed circuit assembly (PCA), printed circuit board assembly or PCB assembly (PCBA). The IPC preferred term for assembled boards is circuit card assembly (CCA), and for assembled backplanes it is backplane assemblies. The term PCB is used informally both for bare and assembled boards.
A soft starter reduces the voltage by “notching” the applied sinusoidal waveform, simulations of which can be seen in Figures 8-13. A notch is a non-technical term for the zero voltage area in the middle waveform seen in Fig. 9. Fig. 9 also shows the forward firing SCR pulses in green and the reverse firing pulses in blue to notch the output voltage. Fig. 10-13 show a progression from a 90º firing angle to 30º. As the notch decreases in size, the Vrms increases along with Irms. An initial voltage, determined by the user, is ramped up to full voltage by varying the firing angle depending on the preset profile of the soft starter. Soft starters can be controlled via open-loop or closed-loop control.
Figure 8: Single Phase Simulation
Figure 9: Single Phase Simulation (90º Firing Angles, Voltage, and Current)
Figure 10: 90º ~ 341Vrms
Figure 11: 70º ~ 405Vrms
Figure 12: 50º ~ 452Vrms
Figure 13: 30º ~ 469Vrms

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