ET 210 Lab 4

QUEENSBOROUGH COMMUNITY COLLEGE Department of Engineering Technology ET 210 Lab 4: Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits Objectives: 1) To plot the characteristics of a Zener Diode. 2) To build a Voltage Regulator circuit using a Zener Diode and Resistors. 3) To consider the typical operating current and voltage of a Light-Emitting Diode (LED). 4) To build a voltage level indicator circuit using LEDs, Zener Diodes, Rectifier Diodes and Resistors 5) To build a polarity indicator circuit using LEDs and a resistor. Equipment Required: DC Power Supply Digital Multimeter Components Required: Zener Diodes: V Z = 5.6 V (1N4734A or equivalent) V Z = 5.1 V (1N4733A or equivalent) Red LEDs: Quantity 2 Green LED General Purpose Silicon Rectifier Diode (1N400X, where X is any digit from 1 to 7): Quantity 4 Resistors (rated 1/2 Watt or above): 220 Ω, 330 Ω, 680 Ω, 470 Ω, 270 Ω, 1 k Ω Lab Experimental Procedure: 1) Measure the resistance value of each resistor and record the results below: Nominal color code value of 220 Ω Measured resistance value = 300 Ω Nominal color code value of 330 Ω Measured resistance value = 335 Ω Nominal color code value of 680 Ω Measured resistance value = 721 Ω QCC ET John Buoncora Page 1

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits Nominal color code value of 470 Ω Measured resistance value = 535 Ω Nominal color code value of 270 Ω Measured resistance value = 301 Ω Nominal color code value of 1 k Ω Measured resistance value = 1.017 k Ω Note: The physical package of a diode is shown in the upper part of the following diagram and the schematic symbol of a Zener Diode is shown in the lower part of the diagram. The band (or stripe) around the physical package of the diode indicates the Cathode. Anode Cathode 2) Construct the circuit of Figure-1: Zener Diode Characteristics Test Circuit. Note that the QCC ET John Buoncora Page 2

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits Use the measured values of the source voltage {E S (measured) } and output voltage {V OUT (measured) } along with the measured resistance value of resistor R 1 to calculate the current in the fourth column of Table-1. E S (specified) E S (measured) V OUT (measured) I R1 = (E S (measured) – V OUT ) / R 1 0 V 0 V 0 V 0 A 1.0 V 1.06 V 1.06 V 2.0 V 2.01 V 2.01 V 3.0 V 3.07 V 3.06 V 4.0 V 4.01 V 4.05 V 5.0 V 5.04 V 5.03 V 5.2 V 5.24 V 5.22 V 5.4 V 5.42 V 5.31 V 5.6 V 5.61 V 5.40 V 5.8 V 5.80 V 5.44 V 6.0 V 6.00 V 5.47 V 6.2 V 6.19 V 5.48 V 6.5 V 6.54 V 5.50 V 7.0 V 6.99 V 5.51 V 7.5 V 7.51 V 5.52 V 8.0 V 8.02 V 5.53 V 8.5 V 8.54 V 5.54 V 9.0 V 9.04 V 5.55 V 9.5 V 9.56 V 5.55 V 10.0 V 10.03 V 5.56 V 11.0 V 11.06 V 5.58 V 12.0 V 12.06 V 5.59 V 13.0 V 13.04 V 5.61 V 14.0 V 14.06 V 5.62 V Table-1: Zener Diode Characteristics QCC ET John Buoncora Page 4

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits 5) Construct the circuit of Figure-2: Voltage Regulator and Load Circuit (with varying input voltage) and initially set the supply voltage E S to 0 V. Use the 1N4734A or equivalent Zener diode, which is rated at a nominal Zener voltage of 5.6 V. Es R1 330 Ω 1N4734A + _ + _ VL IR1 RL 680 Ω Iz IL + _ VR1 Figure-2: Voltage Regulator and Load Circuit (with varying input voltage) 6) Set the supply voltage E S to each of the values specified in Table-2: Data for Voltage Regulator and Load Circuit (with varying input voltage). Next, measure the Load Voltage V L and the voltage V R1 across resistor R 1 , and record your results in Table-2 for each supply voltage setting. E S V L (measured) V R1 (measured) 13.0 V 5.55 V 7.53 V 10.0 V 5.51 V 4.51 V 6.5 V 4.40 V 2.15 V Table-2: Data for Voltage Regulator and Load Circuit (with varying input voltage) 7) Initially, set the supply voltage to 0 V and change the load resistor R L of the circuit that you constructed previously in step 5 to each of the values shown in Table 3: Data for Voltage Regulator and Load Circuit (with varying Load Resistance). Refer to Figure-3: Voltage Regulator and Load Circuit (with varying Load Resistance) for the schematic of the modified circuit. Set the supply voltage E S to 10 V after you connect each value of the Load Resistance ( individually and only one load resistance at a time ) from Table 3. Next, measure the Load Voltage V L and the voltage V R1 across resistor R 1 , and record your results in Table-3 corresponding to each Load Resistance value. QCC ET John Buoncora Page 5

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits of 8 mA to 20 mA). The actual forward voltage of an LED depends on the particular device and varies with current but the change in voltage is relatively small for relatively large changes in current (as with an "ordinary" diode). The "turn on" voltage of the LED (where the LED just starts illuminating dimly at a very low value of forward current) can be a few tenths of a volt below the typical forward-bias voltage levels stated above. 8) Construct the circuit of Figure-4: LED Test Circuit using the Red LED and set the supply voltage V in to 10 V as shown. Vin 10 V R1 1kΩ Red LED + _ VLED + _ + _ VR1 Figure-4: LED Test Circuit 9) Measure the voltage across the LED, which is designated as V LED . V LED = 1.95 V 10) Measure the voltage across resistor R 1 , which is designated as V R1 . V R1 = 8.11 V 11) Initially, set the supply voltage V in to 0 V and then slowly increase the supply voltage V in until the LED just begins to illuminate (the results of this step are subjective and depend on the viewer). Measure the voltage across the LED and the voltage across resistor R 1 and record your measurements below: V LED = 0.19 V (LED just begins to illuminate) V R1 = 0.20 V (LED just begins to illuminate) LED Voltage Level Indicator Circuit : QCC ET John Buoncora Page 7

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits LED1 Red LED2 Red LED3 Green R1 680 Ω 1N400X 1N400X 1N400X R2 470 Ω R3 270 Ω Vin 1N400X 1N4733A Zener rated at 5.1 V + _ Figure-5: Voltage Level Indicator Circuit The circuit shown in Figure-5 is a simple Voltage Level Indicator Circuit. The (approximate) range of the level of input voltage is indicated by the number of LEDs that are illuminated (emitting light) beginning with LED1. The following table summarizes the states of operation (where the maximum input voltage V in (max) is + 10 V): Range of Input Voltage V in LED 1 (Red) LED 2 (Red) LED 3 (Green) 0 V ≤ V in < V A OFF OFF OFF V A ≤ V in < V B ON OFF OFF V B ≤ V in < V C ON ON OFF V C ≤ V in ≤ 10 Volts ON ON ON The input threshold voltage levels of the Voltage Level Indicator Circuit are designated as V A , V B , and V C in the table above. The threshold voltage V A is determined by the "turn on" voltage of LED 1. The threshold voltage V B is determined by the "turn on" voltage of LED 2 and the "turn on" voltages of the four forward-biased 1N400X Silicon diodes. Threshold voltage V C is determined by the "turn on" voltage of LED 3 and the Zener Voltage of the reverse-biased 1N4733A Zener diode. The LED turn on currents and the resistances R 1 , R 2 , and R 3 also influence QCC ET John Buoncora Page 8

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits with the DMM. Complete the table below by recording the measured voltage level of V in (according to the DMM) at each point where LED 1, LED 2, or LED 3 just begins to illuminate. Note that the lower numbered LED or LEDs will remain on when the higher numbered LED turns on (illuminates). See step 13b also for the last row of the table. Measured values of Input Voltage V in at the Thresholds where the LED(s) just begin(s) to illuminate LED 1 (Red) LED 2 (Red) LED 3 (Green) V in = _________________ Just Begins to illuminate OFF OFF V in = _________________ ON Just Begins to illuminate OFF V in = _________________ ON ON Just Begins to illuminate Step 13 Data Table: Measured Input Voltages (V in ) at the Thresholds where the LED(s) Just Begin(s) to illuminate (do not allow V in to exceed 10 V) 13b) Measure the voltage across the 1N4733A Zener Diode for the condition where LED 3 Just Begins to illuminate (last row of Step 13 Data Table) and record the result: V 1N4733A (LED 3 Just Begins illuminating) = _______________________________ 14) Set the input voltage V in to 10 V in the circuit of Figure-5 and measure the voltages indicated below. Note that V R# represents the voltage across resistor R # and V LED# represents the voltage across LED#. V in = _____________________ (actual measured value, which should be close to 10V) V R1 = _____________________ V LED1 = ____________________ V R2 = _____________________ V LED2 = ____________________ V R3 = _____________________ V LED3 = ____________________ LED Polarity Indicator Circuit : QCC ET John Buoncora Page 10

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits Vin 10 V R1 1kΩ LED1 Green LED2 Red + _ XMM1 DMM DMM High DMM Low indicates Vx X Figure-6: Polarity Indicator Circuit (with one possible input polarity shown) The circuit shown in Figure-6 is a polarity indicator circuit. The Green LED will be forward- biased and illuminate for one polarity of the input voltage and the Red LED will be forward- biased and illuminate for the opposite polarity of input voltage. The reverse -bias breakdown voltage of an LED is typically much less than that of an "ordinary" diode and is typically around 5 V, although the level varies between different LEDs. Therefore, LEDs are normally operated in forward-bias and they require protection to keep reverse voltages below the breakdown level if they will become reverse-biased in a circuit. This can easily be achieved by connecting an ordinary diode in parallel with the LED in the opposite direction as shown below (do not build the partial circuit drawn below as it is shown for the purpose of this discussion only): R LED "ordinary" Diode The "ordinary" diode is reverse-biased and acts as an open circuit when the LED is forward- biased (the resistor limits the LED current). However, the "ordinary" diode is forward-biased and has a voltage drop of approximately 0.7 V (assuming a Silicon diode) when the LED is reverse-biased. Since the LED and "ordinary" diode are connected in parallel, the actual voltage across the reverse-biased LED is 0.7 V, which is below the reverse-bias breakdown voltage of the LED. The Polarity Indicator Circuit of Figure-6 contains two LEDs (one Green and one Red) connected in parallel in opposite directions, which serves the dual purpose of providing polarity indication and protection for whichever LED is reverse-biased. 15) Construct the Polarity Indicator Circuit of Figure-6 with the polarity of the input voltage as shown (in Figure-6) and set the supply voltage V in to 10 V. The voltage across the parallel QCC ET John Buoncora Page 11

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits Lab Report Exercises, Calculations, and Questions : 1) Refer to Lab Experimental Procedure steps 2, 3, and 4, which pertain to Figure-1, along with the data in Table-1 : Zener Diode Characteristics for this exercise. Plot the 1N4734A Zener Diode characteristics of zener diode current I D versus zener diode voltage V D . Use the data contained in the V OUT and I R1 columns of Table 1 and the following relationships to construct the plot: V D = – V OUT and I D = – I R1 These relationships imply that V D and I D are both negative since the quantities V OUT and I R1 respectively are both positive in the circuit of Figure-1. Therefore, the plot of the zener diode characteristics will occupy the third quadrant. 2) Copy the value of the measured output voltage V OUT and current I R1 , from the last row of Table-1 when E S (specified) = 14.0 V, below and note that V D = – V OUT and I D = – I R1 . V OUT = ___________________ {when E S (specified) = 14.0 V} I R1 = _____________________ {when E S (specified) = 14.0 V} The data sheet for the 1N4734A specifies a typical value of zener voltage V Z = 5.6 V at zener test current I Z = 45 mA. The data sheet also specifies a 5% tolerance on V Z for the 1N4734A. Calculate the minimum and maximum possible values of the zener voltage according to the information provided above from the data sheet. Calculate the %Difference between V OUT {at E S (specified) = 14.0 V} and V Z (both values are positive). Compare the current value I R1 to the zener test current value of 45 mA and note that the largest value of E S (specified) is 14.0 V. Therefore, the largest zener current that we tested the zener diode at in this experiment is approximately: I R1(maximum) ≈ (14 V - 5.6 v) / (220 Ω) = 38.2 mA, which is 6.8 mA less than the specified zener test current of 45 mA. 3) The zener impedance Z Z is defined as follows: Z Z = ΔV Z / ΔI Z = (V Z2 – V Z1 ) / (I Z2 – I Z1 ) The zener impedance is usually specified at the zener test current (and at the zener knee current). We will calculate the average zener impedance Z Z using the values specified below. QCC ET John Buoncora Page 13

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits Find the average zener impedance using the equation Z Z = ΔV Z / ΔI Z = (V Z2 – V Z1 ) / (I Z2 – I Z1 ) and the values of zener voltage and current corresponding to E S (specified) = 9.0 V and E S (specified) = 13.0 V from Table-1 . 4) Refer to the uppermost row of Table-2 when E S = 13.0 V and refer to Figure-2 for this exercise. Verify that Kirchhoff's Voltage Law (KVL) is satisfied using the values of E S , V L , and V R1 for the Voltage Regulator and Load Circuit of Figure-2. 5) Refer to the Voltage Regulator and Load Circuit of Figure-2 and Figure-3, and refer to the data recorded in Table-2 and Table-3 of Lab Experimental Procedure steps 5, 6, and 7 for this exercise. For each row in Table-2 and Table-3, find the following: Calculate the Load current I L through R L and the current I R1 through R 1 using Ohm's Law, along with the appropriate measured voltage and resistance values. Calculate the current I Z through the Zener Diode using Kirchhoff's Current Law (KCL) and the values of I L and I R1 . 6) Once again, refer to the Voltage Regulator and Load Circuit of Figure-2 for this exercise. In the following calculations, use the nominal values of the components from the schematic of Figure-2 and note that the 1N4734A Zener Diode is rated at a nominal zener voltage of 5.6 V. Calculate the theoretical values of V L , I L , V R1 , I R1 , and I Z for the circuit of Figure-2 when E S = 10.0 V and when E S = 6.5 V . Compare the calculated results to the corresponding measured results. 7) Refer to the Voltage Regulator and Load Circuit of Figure-3 for this exercise. In the following calculations, use the nominal values of the components from the schematic of Figure-3 and note that the 1N4734A Zener Diode is rated at a nominal zener voltage of 5.6 V. Calculate the theoretical values of V L , I L , V R1 , I R1 , and I Z for the circuit of Figure-3 when R L = 1 kΩ and when R L = 220 Ω . Compare the calculated results to the corresponding measured results. 8) Refer to the Data for the Voltage Regulator and Load Circuit of Table-2 and Table-3 for this exercise. State the conditions of supply voltage E S and Load Resistance R L for which regulation of the output voltage was maintained. State the conditions where the output voltage was no longer regulated. 9) Refer to the LED Test Circuit of Figure-4 and refer to the data obtained in Lab Experimental Procedure steps 9 and 10. Verify that the data of steps 9 and 10 along with the value of V in = 10 V satisfies Kirchhoff's Voltage Law (KVL). Compare the measured value of the voltage across the Red LED to the typical value of the LED forward voltage stated in the lab using a QCC ET John Buoncora Page 14

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits 13) Compare the theoretical values of the input threshold voltages that you calculated in exercise 12 to the measured values of the input threshold voltages of V in that were recorded in the Step 13 Data Table. Find the largest %Difference and note that the circuit parameters provided in step 12 are rough approximations of the actual values. 14) Once again, refer to the Voltage Level Indicator Circuit of Figure-5 and assume V in = 10 V . Use the typical values of the parameters provided below to calculate the theoretical values of the voltage across each resistor and the current through each resistor and LED when V in = 10 V . That is, find V R1 , V R2 , V R3 , I R1 = I LED1 , I R2 = I LED2 , and I R3 = I LED3 when V in = 10 V . Circuit Parameter Typical value of Voltage V 1N400X (typical forward-biased voltage, Silicon diode) 0.7 V V F (Red LED) 1.8 V V F (Green LED) 2.2 V V Z (1N4733A) (rated reverse-biased zener voltage) 5.1 V Table to be used with Exercise 14 15) Refer to the data obtained in Lab Experimental Procedure step 14 (for the Voltage Level Indicator Circuit of Figure-5 when V in = 10 V ) for this exercise. Calculate the current through each resistor and LED (I R# = I LED# ) based on the measured data. Compare these current values (exercise 15) to the theoretical current values of exercise 14. Compare the measured values of the LED voltages from Lab Experimental Procedure step 14 to the typical theoretical values provided in Exercise 14. 16) Use the measured values of the voltages from Lab Experimental Procedure step 14 (Figure-5 when V in = 10 V ) and Kirchhoff's Voltage Law (KVL) to find the voltage across each 1N400X diode and the voltage across the 1N4733A zener diode. Assume that each 1N400X diode has the same voltage across it and use algebra along with the information provided above to calculate the voltage across each individual 1N400X diode. Note: We can assume that each 1N400X diode has approximately the same voltage across it only because the 1N400X diodes are all forward-biased, connected in series (carrying the same current), and have the same part number. If the same part number diodes were connected in parallel (same voltage) and even if all were forward-biased, then we could not assume that the diode currents were equal. Small differences in the characteristics of the same part number diodes can result in large differences in diode currents at the same value of diode voltage ( parallel connection) even though the diodes may all be forward-biased (of course, the diode currents are much different if the diodes are connected in parallel and one diode is forward-biased and another diode is reverse-biased). QCC ET John Buoncora Page 16

Zener Diodes, Voltage Regulators, LEDs and Voltage Indicator Circuits 17) Refer to the Polarity Indicator Circuit of Figure-6 and Figure-7, along with the data recorded in Lab Experimental Procedure step 15 and step 16 for this exercise. Based on the schematic of the Polarity Indicator Circuit, explain which LED should turn on for each polarity of input voltage. Are the theoretical and observed results in agreement? Compare the measured value of V X from step 15 to the measured value of V X from step 16. What do each of these values represent? How does the circuit shown in Figure-6 and Figure-7 provide protection for whichever LED is reverse-biased? What is the maximum reverse-biased voltage across each LED when it is reverse-biased in Figure-6 or Figure-7? QCC ET John Buoncora Page 17