The 1N4001 and 1N4004 are diodes, which are switch-like electronic components. When a diode receives voltage in one direction, electricity flows through it. When a diode receives voltage in the opposite direction, the flow of electricity is blocked. Because of that directionality, diodes create a consistent pattern of electricity, and they are often used in power supplies for electronic devices.
One side of a diode is called the anode, and the other side is called the cathode. Most diodes will only conduct electricity when a specific level of positive voltage is connected to the anode and a negative voltage is connected to the cathode. When that condition is met, the diode is "forward-biased." To operate, the 1N4001 and 1N4007 require a forward-bias of around 1V.
If the voltage connections to a diode are reversed -- positive to cathode, negative to anode -- the diode will not conduct. In that instance, the diode is "reverse-biased," and the flow of electricity will be blocked. However, a high level of voltage can overcome the reverse-bias condition, causing "reverse-breakdown." During reverse-breakdown, the diode may conduct electricity, and it may even become damaged. Diodes can withstand a specific level of reverse voltage, which is listed as "peak inverse voltage," "maximum reverse-voltage," or "peak repetitive reverse voltage."
Diode as Rectifier
AC stands for alternating current, which is the type of electricity that travels in household wiring. The polarity of AC constantly moves from a positive peak to a negative peak, in a wave that looks like a sideways letter S. When AC electricity is connected to a diode, the diode alternates between forward-biased and reverse-biased conditions. Because the diodes are conducting only half the time, the negative AC peaks are eliminated and a series of positive peaks is formed. The process of using diodes to change the AC wave is called rectification.
1N4001 and 1N4004 Diodes
The 1N4001 and the 1N4004 are diodes that are generally used for rectification. The only difference between the two is the level of peak repetitive reverse voltage, or Vrrm. As listed on the datasheets, the 1N4001 has a Vrrm of 50V, and the 1N4004 has a Vrrm of 400V. These Vrrm levels mean that the 1N4001 can withstand 50 volts and the 1N4004 can withstand 400 volts, in the reverse-bias condition. If that reverse-bias voltage repeatedly goes above those levels, the 1N4001 and the 1N4004 will not function properly and will become damaged. The Vrrm levels indicate that the 1N4001 is suitable for low voltages, and the 1N4004 is the better choice for high-voltage situations.