 Welcome to diode approximations. The three approximations of a diode. The modeling of a diode. Depending on the application, a diode can be modeled in one of three approximations. The first approximation. Ideal diode. The first approximation of a diode is simply a switch. If the diode is forward biased, the switch is closed. The diode will behave as a conductor with zero ohms of resistance. If the diode is reversed biased, the switch is open. The diode will behave as an open with infinite resistance. The second approximation. The second approximation requires 0.7 volts of forward bias to overcome the barrier potential. When reversed biased, no current will flow. When forward biased, 0.7 volts appears across the diode and current will flow. The third approximation. The third approximation includes both the 0.7 volts barrier potential and the internal resistance of the diode, called the bulk resistance. Shown here is reverse bias. And shown here is forward bias. When are the difference approximations used? The first approximation. This is used primarily in troubleshooting. Is the diode conducting or not? Second approximation. This is used when a more accurate determination of load current and voltage is required. And third approximation. This is used during the original design of the diode circuits. Let's match the approximation term to the correct schematic depiction. First approximation. Second approximation. And third approximation. Remember, depending upon your application, the proper approximation should be used. So let's recap. First approximation. This is used primarily in troubleshooting. Is the diode conducting or not? Second approximation. This is used when a more accurate determination of load current and voltage is required. And third approximation. This is used during the original design of the diode circuits. Congratulations! You have now completed this activity on diode approximations. And if you like this video, give us a thumbs up.