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| university:courses:electronics:electronics-lab-window-comp-tmp01 [06 Mar 2018 17:57] – Antoniu Miclaus | university:courses:electronics:electronics-lab-window-comp-tmp01 [07 Mar 2018 12:36] – add tmp01 background and programming Antoniu Miclaus |
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| 1 – 470Ω resistor\\ | 1 – 470Ω resistor\\ |
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| ===== Background ===== | ===== Window Comparator ===== |
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| | ==== Background ==== |
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| Consider the circuit presented in Figure 1. | Consider the circuit presented in Figure 1. |
| The circuit uses a voltage divider network, formed of three equal value resistors R1 = R2 = R3. The voltage drops across each resistor will also be equal at one-third of the reference voltage (V<sub>REF</sub>). Therefore, the upper reference (V<sub>REF(HIGH)</sub>) is set to 2/3V<sub>REF</sub> and the lower reference to 1/3V<sub>REF</sub>. | The circuit uses a voltage divider network, formed of three equal value resistors R1 = R2 = R3. The voltage drops across each resistor will also be equal at one-third of the reference voltage (V<sub>REF</sub>). Therefore, the upper reference (V<sub>REF(HIGH)</sub>) is set to 2/3V<sub>REF</sub> and the lower reference to 1/3V<sub>REF</sub>. |
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| Considering that we use the When V<sub>IN</sub> is below the lower voltage level, (V<sub>REF(LOW)</sub>) which equates to 1/3V<sub>REF</sub>, the inverted output will be HIGH (non-inverted output will be LOW) and D1 will be forward biased, driving the Q1 transistor. When V<sub>IN</sub> exceeds this 1/3V<sub>REF</sub> lower voltage level, the first comparator detects this and switches the inverted output to be LOW (non-inverted output HIGH). | Considering that we use the When V<sub>IN</sub> is below the lower voltage level, (V<sub>REF(LOW)</sub>) which equates to 1/3V<sub>REF</sub>, the output will be HIGH and D2 will be forward biased. Due to the positive voltage at base the npn transistor, Q1 moves into the saturation. Thus, the output voltage is zero, and the supply voltage will drop on R5 and D3, turning the LED on. |
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| | When V<sub>IN</sub> exceeds this 1/3V<sub>REF</sub> lower voltage level and it is below 2/3V<sub>REF</sub> (V<sub>REF(HIGH)</sub>), both comparators' outputs will be LOW and the diodes reverse-biased. No voltage is applied to the base of Q1,the transistor is in cut-off and no collector current flows through R6 or R5, D3. The output voltage is the supply voltage V+. |
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| | When V<sub>IN</sub> is above the upper voltage level, (V<sub>REF(HIGH)</sub>) which equates to 2/3V<sub>REF</sub>, the output will be HIGH and D1 will be forward biased. Due to the positive voltage at base the npn transistor, Q1 moves into the saturation. Thus, the output voltage is zero, and the supply voltage will drop on R5 and D3, turning the LED on. |
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| | ==== Hardware Setup ==== |
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| | Build the following breadboard circuit for the window comparator circuit. |
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| | <WRAP centeralign>{{:university:courses:electronics:window_comp-bb.png|}}</WRAP> |
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| | <WRAP centeralign> Figure 2. Window Comparator breadboard circuit </WRAP> |
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| | ==== Procedure ==== |
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| | Use the first waveform generator (W1) as source to provide a Triangular signal with 5V amplitude, 100Hz frequency and 2.5V offset. |
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| | Use the second waveform generator (W2) as 5V constant reference voltage. |
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| | Supply the circuit using the 5V power supply. |
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| | Configure the scope so that output signal is displayed on channel 2 and the input signal is displayed on channel 1. |
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| | A plot example is presented in Figure 3. |
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| | <WRAP centeralign>{{:university:courses:electronics:window_comp-wav.png|}}</WRAP> |
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| | <WRAP centeralign> Figure 3. Window Comparator waveforms </WRAP> |
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| | On the plot the "windows" can be noticed when the input voltage is between the upper and the lower voltage references. |
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| | ===== Temperature Control ===== |
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| | ==== Background ==== |
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| | An example of a window comparator application is a simple temperature controller circuit (Figure 2). The temperature sensor, TMP01, has the dual comparator configuration of figure 1 built in. By choosing the proper values for R<sub>1</sub>, R<sub>2</sub> and R<sub>3</sub> the circuit monitors if the temperature holds in the required range (25 ± ~10 °C). |
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| | The TMP01 is a linear voltage-output temperature sensor, with a window comparator that can be programmed by the user to activate one of two open-collector outputs when a predetermined temperature set point voltage has been exceeded. A low drift voltage reference is available for set point programming. By connecting the two open collector outputs together as a single wire OR output we can obtain a signal which is at a logic high when the ambient temperature is within the target window. |
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| | <WRAP centeralign>{{:university:courses:electronics:tmp01_window_comp-sch.png|}}</WRAP> |
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| | <WRAP centeralign> Figure 4 Temperature sensor window comparator </WRAP> |
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| | ==== Programming TMP01 ==== |
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| | In the basic fixed set point application utilizing a simple resistor ladder voltage divider, the desired temperature set points are programmed in the following sequence: |
| | 1. Select the desired hysteresis temperature. |
| | 2. Calculate the hysteresis current I<sub>VREF</sub>. |
| | 3. Select the desired set point temperatures. |
| | 4. Calculate the individual resistor divider ladder values needed to develop the desired comparator set point voltages at SET HIGH and SET LOW. |
| | The hysteresis current is readily calculated. For example, for 2 degrees of hysteresis, I<sub>VREF</sub> = 17 μA. Next, the set point voltages, V<sub>SETHIGH</sub> and V<sub>SETLOW</sub>, are determined using the VPTAT scale factor of 5 mV/K = 5 mV/(°C + 273.15), which is 1.49 V for 25°C. Then, calculate the divider resistors, based on those set points. The equations used to calculate the resistors are: |
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| | V<sub>SETHIGH</sub> = (T<sub>SETHIGH</sub>+ 273.15) (5 mV/°C) |
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| | V<sub>SETLOW</sub> = (T<sub>SETLOW</sub> + 273.15) (5 mV/°C) |
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| | R<sub>1</sub> (in kΩ) = (V<sub>VREF</sub>−V<sub>SETHIGH</sub>)/I<sub>VREF</sub>= (2.5 V −V<sub>SETHIGH</sub>)/I<sub>VREF</sub> |
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| | R<sub>2</sub> (in kΩ) = (V<sub>SETHIGH</sub>−V<sub>SETLOW</sub>)/I<sub>VREF</sub> |
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| | R<sub>3</sub> (in kΩ) = V<sub>SETLOW</sub>/I<sub>VREF</sub> |
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| | The total R<sub>1<sub> + R<sub>2</sub> + R<sub>3</sub> is equal to the load resistance needed to draw the desired hysteresis current from the reference, or I<sub>VREF</sub>. |
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| | I<sub>VREF</sub> = 2.5/( R<sub>1</sub> + R<sub>2</sub> + R<sub>3</sub>) |
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