diode is called a valve
The diode passes the current in one direction (anode to the cathode), and blocks the current in the opposite direction (cathode to anode). so it is used in reverse voltage protection circuitry and mostly in ac repair. almost all ac rectifier circuit to dc use diode for its character. because you probably know ac has one half positive and one half negative ie ac repeatedly change its voltage from + 311v to -311v and change its positive voltage peak to peak negative voltage in 10 milliseconds (220v, 50hz). so normal human eyes can not see this rapid change.
So what the diode does, passes the positive half and blocks the negative half, yields only half positive (half wave). although it will have very low efficiency (approximately 40%), so usually we use a combination of four diodes and we get both half positive (full wave). now just use the capacitor we get dc.And because the diode is a single passage (unidirectional), it works like a water valve, so it is also called a valve.
A valve is a device for controlling the liquid ducts through pipes or channels. a transistor diode or device used to control the flow of charge or current can be called an electronic valve. term valve is the primary used in Indonesia. in the past, we call it tube vacuum tube.The British call it a thermionic valve or valve.
The diode controls the current flow as the valve is not for the liquid. this is a more accurate obsolete term for old vacuum tubes where it is more difficult for them to act as an on / off switch and instead have the current gradient as a more suitable application. Today’s semiconductor devices are efficient enough to act effectively as switches, and hence this term is becoming obsolete.
Since electrons are negatively charged particles, the electrons will only be attracted to the anode if it is given a positive potential with regard to the cathode. this explains why the valve only does one direction, from cathode to anode, and not vice versa. it also explains the choice of the word ‘valve’ to describe the device, since the valve is, by definition, a one-way device.The diode valve is so called because it has only two electrodes – cathode and anode.
This corresponds to the two electrodes of the original diode valve, the cathode being a heated electrode and emitting electrons, and the anode being the electrode collecting the electrons.
Since electrons are negatively charged particles, the electrons will only be attracted to the anode if it is given a positive potential with regard to the cathode. this explains why the valve only does one direction, from cathode to anode, and not vice versa. it also explains the choice of the word ‘valve’ to describe the device, since the valve is, by definition, a one-way device. However, Americans never use this term and always refer to them as ‘vacuum tubes’.
