Video Lectures created by Tim Feiegenbaum at North Seattle Community College.
Typical electronic components include--we have three groups here. I'm going to be looking at Voltage Sources, Fuses and Circuit Breakers, so this will be part A. Then we're going to be looking at Resistors in the second section that will be 3.3 B. I hope to conclude this with Capacitors, Inductors, Transformers, Transistors and Diodes. This would be in the third section, 3.3 C. I don't think a D will be needed. We're planning to do it as A, B and C.
Okay, first thing we're going to look at is batteries. A cell is a stand-alone source of energy. A battery is two or more cells connected together to provide higher voltage and/or current to a circuit. The more cells the higher the voltage supply. Cells and batteries are rated by voltage and ampere-hour ratings. Ah stands for ampere-hour. One Ah means: The battery can deliver one amp of current for one hour or 1/4 amp of current for four hours, or 2 amps of current for 30 minutes. You have laws of variation here. This is the concept of an Ah. Here we have a symbol for a battery. The longer terminal here is the positive side and the shorter side is the negative side.
Excessive current flow in an electrical circuit may damage the circuit. Now that's probably quite obvious. You have too much current flowing through a circuit, it will overheat and it can burn up and destroy components. Typical causes of increased current flow are low-resistance connections outside the normal path of current flow. These are called short circuits. Fuses and circuit breakers provide protection from excessive current flow. That is a schematic symbol for a fuse.
Fuses are connected so that current flowing through the circuit also flows through the fuse. Here we have a fuse, and I suppose we could go in here and connect a battery. We could come back over here and go up like so and connect a ground here. We would have a circuit. Fuses are connected so that current flowing through the circuit also flows through the fuse. The fuse becomes a part of the circuit. A resistive link inside the fuse heats up when current flows through it. Excessive current flow causes the link to burn, which stops the current flow and protects the circuit. In this case, here are the fuses in the circuit. If we're pulling too much current through this then the fuse will burn and will have an open at this point and current will cease to flow. A fuse that has burned open is said to be, and here's the term, a blown fuse.
Fuses have three electrical ratings. We're going to look at Current ratings, Voltage ratings and Response time. First of all, current rating: Max sustained current that can flow through the fuse without it opening. The voltage rating: The minimum amount of voltage required to ark across the fuse after it blows. Notice that it's after it blows. The voltage rating of the fuse must exceed the highest voltage that can be expected across the circuit. If the voltage rating is exceeded, the blown fuse can ark defeating the purpose of the fuse.
Response time: When the current exceeds its rating, the fuse link will burn open. It takes a certain amount of time for the fuse link to disintegrate. This time is referred to as the “response time.” Response times vary from several milliseconds to several seconds. Due to the type of circuit, the response time will have to meet those needs. If you have real sensitive circuits and they have a fast response time. Not so sensitive circuits would not need a quick response time.
Fuses may be classified according to their appropriate response times. We have three. There is the Slo-blo, the Fast-blo, and the Normal-blo. First of all, let's look at Slo-blo. These fuses are designed to withstand currents which greatly exceed their current rating as long as the over current condition is only momentary. Short term transients or surges won't typically blow this type of fuse and the response time of 1/10 to 10 seconds. There's a term that is slo-blo. These are usually in a household. You would have slo-blo fuses if you have transients or surges in the voltage line. Those will not blow. If they did you'd have to be resetting the circuit breaker all the time because surges and transients are really quite common.
Then there is the Fast-blo. These have a very short response time. They protect sensitive electronic components like transistors. They range from sub millisecond through hundreds of milliseconds. These could be less than a millisecond of time in the response. They are very fast. Then there are Normal-blo: response time between slo-blo and fast acting, so this would be in between the slow and the fast.
Circuit breakers also provide over current protection for electrical devices but, unlike fuses, do not have to be replaced after they have opened the circuit. A circuit breaker that has opened in response to over current is said to be, and here's the term, tripped. Circuit breakers have the advantage of being reused in a circuit, but typically, have slower response times than fuses. This means they are tolerant to short term over voltages and won't protect sensitive electronic equipment. This is why surge protectors are needed on sensitive electronic equipment like computers.
Okay, this was a quick lesson we looked at. Circuit breakers, fuses. We looked at the different ratings of fuses and we looked at batteries. This introduces electronic components. The next section, 3B, we'll be looking at resistors.
Video Lectures created by Tim Fiegenbaum at North Seattle Community College.
In Partnership with Future Electronics
by Aaron Carman
by Jake Hertz