In electricity, what is the meaning of the word “bypass”?

1. Basic concept

• In electricity, "bypass" refers to providing an alternative path for electric current to bypass a certain element, circuit, or part of a device. This alternative path is usually connected in parallel with the main path. When certain conditions are met (such as a signal of a specific frequency or a current exceeding a certain amplitude), the current will preferentially or partially pass through the bypass.

2. Application scenarios

• Principle: In electronic circuits, a capacitor is often connected in parallel across an element as a bypass capacitor. For example, in an amplifier circuit, a capacitor is connected in parallel across the emitter resistor of a transistor. For an AC signal, the capacitive reactance

• Capacitor bypass

Principle: In electronic circuits, a capacitor is often connected in parallel across an element as a bypass capacitor. For example, in an amplifier circuit, a capacitor is connected in  parallel across the emitter resistor of a transistor. For an AC signal, the capacitive reactance Xc=1/(2Πfc) (where f is the frequency of the AC signal and C is the capacitance). When the frequency is high enough, the capacitive reactance is very small, and the AC signal will form a bypass through this capacitor and bypass the emitter resistor. The advantage of this is that it can stabilize the DC operating point of the amplifier and at the same time enable the AC signal to be amplified more effectively.

Effect: Through capacitor bypass, the loss of AC signals on resistors can be reduced and the AC gain of the circuit can be increased. Moreover, in power supply filtering circuits, bypass capacitors also play a key role. Connecting a large-capacitance capacitor in parallel at the output of the power supply can provide a bypass for high-frequency noise signals, making the DC voltage output by the power supply more smooth and avoiding interference from high-frequency noise to subsequent circuits.

Bypass diode

Principle: Bypass diodes are used in some circuits. For example, a diode is connected in parallel across the coil of a relay. When the relay coil is de-energized, the coil will generate a reverse electromotive force. This reverse electromotive force may damage other elements connected to the relay coil. The bypass diode provides a discharge path for this reverse electromotive force, and the current will form a bypass through the diode to avoid the influence of the reverse electromotive force on other elements.

Effect: Protect other elements in the circuit from being damaged by the reverse electromotive force generated by inductive elements (such as relay coils, transformer windings, etc.) when the current changes suddenly. In some circuits that need to quickly turn off inductive loads, bypass diodes are a simple and effective protection measure.

Bypass switch or jumper

Principle: In some complex circuit testing or debugging processes, bypass switches or jumpers are set. For example, on a circuit board containing multiple functional modules, in order to test the performance of a certain module, other modules can be temporarily short-circuited (forming a bypass) through a bypass switch, so that the test signal can act directly on the target module and avoid interference from other modules.

Effect: Facilitate circuit debugging and fault diagnosis. When repairing electronic equipment, by using bypass switches or jumpers, faulty modules can be quickly located to determine whether it is a problem with a certain module itself or a problem with the connection or interaction between modules.