CAPÍTULO II: MARCO TEÓRICO
2.3. Bases teóricas
2.3.2. Comprensión de textos
The ability to trace current through an unfamiliar electronic circuit is an important skill for an electronics technician. The rules are very simple, but to effectively implement the rules requires substantial practice. The rules are as follows:
1. Start at the most negative point in the circuit and move toward the most positive point.
2. Trace through the circuit using any path with the following conditions:
a. never violate the basic behavior of a component, and
b. never return to a point in the circuit where you have already traced without first passing through a power source.
Your goal will be to return to the positive side of the power source. If you can make the complete trip, then you know there is current flow in the circuit, and you know the path where it flows. The first condition under item two cautions against violating the basic behavior of a component. This often refers to components that are polarized (LEDs, for example). You would be violating the basic behavior if you traced through a polarized component in the reverse direction.
EXAMPLE SOLUTION
Trace all current paths through the circuit shown in Figure 3-34.
EXAMPLE SOLUTION
We start at the most negative point in the circuit (the negative side of the voltage source). As we trace through the circuit, we pass through R6, R5, R4, R3, R2, and R1. We then complete our journey by returning to the positive side of the voltage source. Since there was only a single path for current, we know this must be a series circuit. The traced current path is shown in Figure 3-35.
Trace current beginning at the negative source terminal and continue until the positive source terminal is reached.
Avoid retracing current paths.
Trace the current in this circuit.
R1
Figure 3-35. Current leaves the negative side of the voltage source, flows through the circuit, and returns to the positive side of the source.
EXAMPLE SOLUTION
Trace all current paths through the circuit shown in Figure 3-36.
EXAMPLE SOLUTION
We start at the negative side of the voltage source. As we move upward, we come to a deci-sion point. According to the rules, we can go in either direction as long as we don’t violate one of the stated conditions. Let us first go to the left through R1, R2, and R3. After passing through R3, we are faced with another decision. Do we con-tinue on through R6 or do we return to the posi-tive side of the voltage source? Since our goal is to reach the positive terminal of the voltage
source, we elect this option. It is interesting to note, however, that if we had continued through R6,, R5, and R4, we would have returned to a point where we had already traced without having gone through a power source. This would have violated one of our tracing rules, so that is not an acceptable path.
Now let us return to the junction of R1 and R4 and trace to the right through R4, R5, and R6. After tracing through R6, we can return to the positive side of the battery. Note that this last segment does not represent a violation of our tracing rules since we have made it to the posi-tive voltage terminal. Figure 3-37 shows our traced paths.
EXAMPLE SOLUTION
Trace all current paths for the circuit shown in Figure 3-38.
EXAMPLE SOLUTION
We can start at the negative side of the volt-age source and move toward the lower ends of R4 and R5. Here the current will split. One portion will flow upward through R4, while the remaining portion will flow through R5. At the upper ends of R4 and R5, the two branch currents will recombine and flow to the left toward R1, R2, and R3. When the
Trace the current paths in this circuit.
R2
Tracing of the current paths for the circuit shown in Figure 3-36.
R2 R1 R3
R4 R5 +
–
Figure 3-38.
Trace the current paths for this circuit.
After exiting resistors R1 and R2, the current recombines and returns to the positive side of the voltage source. These current paths are shown in Figure 3-39.
Practice Problems Practice Problems
1. Trace the current paths for the circuit shown in Figure 3-40.
2. Trace the current paths for the circuit shown in Figure 3-41.
R2 R1 R3
R4 R5 +
–
Figure 3-39. Current paths for the circuit shown in Figure 3-38.
R1 R2
R3
R4
R5 R6
R7 +
–
Figure 3-40. Trace the current through this circuit.
R1 R2
R3
R6 R4
R5 +
–
Figure 3-41. Trace the current through this circuit.
3. Trace the current paths for the circuit shown in Figure 3-42.
Answers to Practice Problems
A light-emitting diode (LED) will only allow current to flow in one direction. If it is connected such that the electron current tries to flow against the arrow on the sche-matic symbol, it offers little opposition to current flow. If it is connected in the reverse
R1
R2 R5
R4 R3
+ –
Figure 3-42. Trace the current through this circuit.
1. 2.
3.
R1 R2
R3
R4
R5
R6
R7 +
–
R1 R2
R4 R3
R5 R6
+ –
R1
R2 R5
R4 R3
+ –
Exercise Problems 3.3 Exercise Problems 3.3
direction, it prevents current flow through the LED. Use this information and your knowledge of circuits to work the following exercise problems.
1. Trace the current paths for the circuit shown in Figure 3-43.
2. Trace the current paths for the circuit shown in Figure 3-44.
3. Trace the current paths for the circuit shown in Figure 3-45.
R1
R2 R3
D1 +
–
Figure 3-43. Trace the current through this circuit.
R1
R2
R3
R4 D2 D1
– +
Figure 3-44. Trace the current through this circuit.
R1
R2 R3
D1 R4 +
–
Figure 3-45. Trace the current through this circuit.