UM0277 STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 32
Technical content
Datasheet sections
- 1 Kit introduction
- 1.1 Package contents
- 1.2 Board presentation
- 2 Functional description
- 2.1 Performances
- 2.2 Ensured functions
- 2.2.1 Temperature control
- 2.2.2 Compressor control
- 2.2.3 Light bulb and buzzer operation control
- 2.2.4 Defrost resistor (or fan) control
- 2.3 Hardware features
- 2.3.1 ACS and ACST devices
- 2.3.2 ST7LITE39F2 microcontroller
- 2.3.3 Capacitive power supply
- 2.4 Graphic user interface (GUI)
- 3 Getting started
- 3.1 Load power
- 3.2 Measure points
- 3.3 Pulse control
- 3.4 Getting started
- 3.4.1 Using the GUI software
- 3.5 GUI windows description
- 3.5.1 Temperature control
- 3.5.2 Timing control
- 3.5.3 Force debug
- 3.5.4 Parameter measurements
- 4 Conclusion
Cold Thermostat Kit based on AC switches and ST7LITE MCU Introduction The STEVAL-IHT001V1 Thermostat Kit (figure below) is designed to control a refrigerator or a freezer. This thermostat kit enables the control of a single-phase induction motor, a light bulb and a defrost resistor (or a fan) working on 230 V RMS 50/60 Hz mains voltage. The board can operate in an ambient temperature range of 0 to 40 °C. The exact maximum temperature depends on the power of the loads (Section 3.1: Load power). The kit includes a Graphic User Interface (GUI) for sending commands to the ST7LITE39F2 Microcontroller or to access MCU information via the Serial Communication Interface (SCI). This enables users to easily change MCU software parameters and acquire measurements during appliance testing. This document provides all the information needed to make the board work (how to connect it, how it works). For specific information about modifying MCU parameters, please refer to the “Help” section of the GUI software. STEVAL-IHT001V1 Thermostat Kit The main goals of this tool are:
- Evaluate full ST solution (microcontroller + AC switch) for cold thermostat applications
- Measure and save the appliance main parameters during operation (load status, compressor operation duty cycle and running period, evaporator temperature)
- Check and analyze efficiency gains by reducing the Hysteresis threshold or adapting the defrost resistor management
- Check the board immunity against fast transient voltages (without GUI connection).
1 Kit introduction
1.1 Package contents
- A thermostat board (ref.: STEVAL-IHT001V1)
- A M2020 5k NTC thermistor from EPCOS (ref.: M2020/5k/A17)
- A CD-ROM, including products presentations and data-sheets, user manual, Application Notes and the GUI software.
- “Getting Started” User Manual (this document)
- The insulated PC interface board (ref.: MC/UNI/0001.01 PC-INTERFACE ver.1.1)
- A 230VAC/9VDC insulated power supply for the SCI interface board
- One RS-232 Interface cable
- One SCI Interface cable
Figure 1. Package contents
1.2 Board presentation
Figure 2 shows the STEVAL-IHT001V1 board and the main components used on this board. Figure 2. Power board (top view)
- A capacitor power supply. The average output current of the capacitor power supply is approximately 25 mA with he embedded 1µF C3 capacitor (for a 230V-50Hz Line RMS voltage)
- A ST7LITE39F2 MCU
- AC Switches: one ACS102-6TA, one ACS110-7SB2 and one ACST6-7ST to control respectively a light bulb, a defrost resistor or fan, and a compressor
- ON/OFF LED. This LED switches ON when the board is powered
- Temperature order visualization. Three LEDs indicate the temperature order using three different settings: low, medium and high
- BP1 Push Button, to change the temperature order setting
- Transducer (or buzzer) to warn the user if the door is opened for an extended time
- SCI connector, for communication between the board and a computer (using the GUI software)
- An In-Dart connector, to load the firmware in the MCU Warning: To avoid electrical shock through the computer, if the In-Dart connector is used to connect a computer, the STEVAL- IHT001V1 board must be plugged into an insulated mains plug. Temperature order visualization BP1 Push Button (temperature selection) J1 connector (AC mains) ON/OFF Led SCI connector Transducer ACS / ACST Power supply capacitor ST7Lite MCU Temperature order visualization BP1 Push Button (temperature selection) J1 connector (AC mains) ON/OFF Led SCI connector Transducer ACS / ACST Power supply capacitor ST7Lite MCU J1 connector (AC mains) ON/OFF Led SCI connector Transducer ACS / ACST Power supply capacitor ST7Lite MCU
2 Functional description
2.1 Performances
- Medium-end appliances: this thermostat board can control the loads traditionally used in medium-end cold appliances (compressor, light, defrost resistor).
- Electromagnetic Compatibility: the board is able to withstand bursts of more than 2.3kV during IEC61000-4-4 standard tests without any operational problems (and up to 4.5kV without any damage). Surge tests have also been performed (IEC61000-4-5 standard): 2 kV bursts can be applied without any damage for the semiconductors.
- Safety standards have also been taken into account. A 2-mm creepage is ensured between all high voltage parts and low voltage parts (to achieve the functional insulation level). The (NTC) thermistor is a class II sensor, and can be put on non- earthed accessible and conductive parts.
2.2 Ensured functions
2.2.1 Temperature control
by changing the value of the resistor placed in series with the NTC (refer to Appendix A).
- Memory area savings
- Easy way to measure the temperature. Temperature regulation is achieved by Hysteresis control (see Figure 3).
Figure 3. Hysteresis law
UM0277 Functional description The linear temperature information is then simply compared to the temperature order. TEMP1 is the upper limit of the Hysteresis cycle. It is equal to the temperature order plus a threshold value (Temperature Hysteresis divided by 2). TEMP2 is equal to the same temperature order minus this threshold. The compressor is switched on if the detected temperature is above TEMP1, and switched off when this temperature becomes lower than TEMP2. The temperature order can be set to low, medium or high levels using the GUI software or using push button PB1 on the board. Moreover, the Hysteresis value can only be changed using the GUI software. For more information, see Section 3.5.1: Temperature control.
2.2.2 Compressor control
An ACST6-7ST AC switch (refer to mark Q1 in Appendix C) is used to turn on and off the compressor according to the evaporator temperature detected by the NTC thermistor. Note that such compressor motors usually present an auxiliary winding that only works during the first seconds of operation in order to apply a higher torque at start-up. A PTC thermal resistor is used to switch off this winding after start-up. In the STEVAL-IHT001V1 thermostat kit, this PTC is not replaced by a TRIAC as proposed on our previous THERM01EVAL kit (refer to AN1354).
2.2.3 Light bulb and bu zzer operation control
A light bulb is driven by the ACS102-6TA AC switch (refer to mark Q3 in Appendix C). This device is ON or OFF when the “Door” switch (J12) is opened or closed respectively. Instead of using the switch placed on the board (J12), one can connect an external switch using the “Door” connector (J13). Note that if the fridge door or the “Door switch” is in “open” position more than one minute, the buzzer will ring and the LEDs will flash. The buzzer can be stopped by pressing the “temp selection” button or using the GUI software (refer to the Help menu of the GUI). When the door is open, the temperature order can only be changed using the GUI software. Note that a resistor (R1) has been added in series with ACS102-6TA AC switch (Q3). Indeed, at the end of the lamp lifetime, the filament breaks and the overall filament can be short-circuited by the flashover resulting in a load current that is no longer limited. This current can exceed the i².t capability of the ACS and destroy it (refer to AN1172). To avoid destroying the ACS102 switch at each lamp flashover, a power resistor is added in series with the light. This resistor (refer to the Appendix C) is rated in order to limit the ACS current to its ITSM value (10 A for a 10 ms half sinus conduction). In this case, a 33Ω1/2 W resistor is sufficient.
2.2.4 Defrost resistor (or fan) control
The defrost resistor is driven by the ACS110-7SB2 AC switch (refer to mark Q2 in Appendix C). This device is ON following the “Defrost activation delay” parameter time defined using the GUI software. This time is compared to the sum of Q1 TRIAC ON times. When this sum is higher than the “Defrost activation delay”, Q2 TRIAC is switched ON (Figure 4). But the software (MCU) waits for the next compressor conduction cycle before turning on the Defrost. Then, the Defrost is switched on when the evaporator temperature is the higher value. This helps reduce power consumption and improve appliance efficiency. Switch Q2 remains on during the “Defrost duration” parameter defined on the GUI software.
Figure 4. Defrost activation principle and also speeds up the defrost process.
2.3 Hardware features
2.3.1 ACS and ACST devices
switches and traditional TRIACs. Table 1. Differences between ACS/ACST and TRIACs
2.3.2 ST7LITE39F2 microcontroller
- No crystal oscillator or external resonator is used. Indeed, the internal RC-oscillator of the ST7LITE39F2 is used to generate the clock.
- No external RESET circuit is used, due to the internal circuit of the ST7LITE39F2. In case of MCU firmware change, four options have to be set:
- Software watchdog activation
- RC oscillator selection
- PLL disabled
- Low Voltage Detection selection
2.3.3 Capacitive power supply
(nominal C3 capacitor value -10%, 198 VRMS line voltage), for a 50Hz mains frequency. Table 2. Maximum average current sunk by the board MCU 2.5mA Maximum supply current in Run Mode. polarity in order to reduce the current consumption.
In order to reduce the surge current, a R6 resistor is used in series with the C3 capacitor. RMS line voltage and 50/60 Hz mains frequency). One particularity of the STEVAL-ITH001V1 board power supply is to be a “negative” one. only be triggered by a negative current (i.e. sourced from the gate).
2.4 Graphic user interface (GUI)
- Sliding buttons to change MCU parameters: – temperature hysteresis – evaporator temperature order – gate current pulse widths and delays – time before defrost activation and defrost duration – ZVS delay (synchronization of MCU commands with the mains voltage)
- Virtual graduated potentiometer to set the evaporator temperature between low, medium or high levels
- Virtual switch to force the loads to ON or OFF states (Light, Defrost, Compressor) for easier board validation
- Measurement and storage of several parameters during operation (duty cycle and running period of the compressor, evaporator temperature evolution, mains frequency and loads status)
Table 3. Maximum output DC average currents
3 Getting started
3.1 Load power
AN1354 for more information on single-phase compressor control. RMS current lower than 1 A) instead of a defrost resistor without any additional snubber.
3.2 Measure points
defines the measurement points. Figure 5. Measurement points (top layer view)
3.3 Pulse control
- T1 is the mains voltage / compressor current phase shift. It helps to apply the gate current pulse just when the Q1 current reaches zero, in order to control the compressor in full cycle mode. Rq: a higher delay could be applied to test the compressor in phase angle mode.
- T3 is the gate current pulse width for switch Q1 (compressor)
- T2 is the gate current pulse width for switches Q2 and Q3 (light bulb and defrost resistor)
Figure 6. Timing definition for gate current pulses Note: The gate currents are negative (i.e. they are sunk from the gates). Table 4. Measurement points
3.4 Getting started
Warning: The Kit is not electrically isolated from the AC input. The MCU is directly linked to the mains voltage. No insulation is ensured between the accessible parts and the high voltage. The STEVAL-IHT001V1 Kit must be used with care and only by persons qualified for working with electricity at mains voltage levels. All measurement equipment must be isolated from the mains before powering the board. When using an oscilloscope with the Kit, it is safer to isolate it from the AC line. This prevents a shock from occurring as a result of touching any SINGLE point in the circuit, but does NOT prevent shocks when touching TWO or MORE points in the circuit. To operate the STEVA-LIHT001V1 board correctly, use the following procedure:
- Connect the NTC thermistor to the “NTC” connector on the thermostat board.
- Connect the DOOR switch (if you use an external door switch) to the “Door” connector on the thermostat board
- Push the board “Door” switch to the “Close” position in order to allow “temperature selection” push-button operation
- Connect the loads on the thermostat board: – Compressor to “MOTOR” connector – Defrost resistor to “DEFROST” connector – Light bulb to “LIGHT” connector
- In case of control with a computer (using the GUI), please go to Section 2.3.3: Capacitive power supply).
- Apply the mains wire to the “MAINS” connector. Plug this wire to the mains voltage.
- After a few seconds: – The “ON/OFF” green LED must light ON – The “medium” red LED must light ON – The compressor switches ON if the sensed temperature is above the temperature order (should be the case if the NTC thermistor is at ambient temperature). – The Light Bulb is switched ON if th e DOOR switch is on “open” position.
- Troubleshooting: – If no LED is ON: replace the fuse. – If LEDs seem OK, unplug the board from the mains. Discharge the VDD supply with a short-circuit between VDD and GND. Plug back the board to the mains. Note: The temperature order can be changed using the BP1 push button on the thermostat board. Each time the BP1 push button is pressed, the red LEDs light on alternatively. Note: If the “Door” Switch is in “Open” position or if the fridge door is opened, the temperature order cannot be changed from the thermostat board (only by using the GUI software).
3.4.1 Using the GUI software
“System” icon on the Control Panel.
- Put the companion CDROM into the PC.
- Browse the CDROM directory to locate the GUI setup executable.
- Double-click on the GUI setup executable file.
- Follow the instructions as they appear on the screen. Figure 7 explains how to connect the different STEVAL-IHT001V1 kit boards and the computer.
Figure 7. STEVAL-IHT001V1 thermostat kit connections
Figure 8. Interface board
- Connect the insulated PC interface board to the PC via the RS232 Interface cable and
to the thermostat board via the SCI Interface wire.
- Connect the 230V/9V insulated power supply to the SCI interface board. First check
position and the Polarity switch to the “Positive” position (Figure 9).
- In case of a problem, ensure that the “selected Serial Communication Port number”
(COM1 or COM2) in the options dialog box is correct.
- In order to enable communication between the GUI software and the thermostat board,
it is necessary to push the “connected” button (“Connected” LED switch ON). Note: Refer to the “Help” menu of the GUI software for more information.
Figure 9. 230V/9V insulated power supply configuration
3.5 GUI windows description
3.5.1 Temperature control
- If “Thermostat order” or “LED temperature” = High, then the Evaporator Temperature Order is “Evaporator Temperature Order 1".
- If “Thermostat order” or “LED temperature” = Medium, then the Evaporator Temperature Order is “Evaporator Temperature Order 2".
- If “Thermostat order” or “LED temperature” = Low, then the Evaporator Temperature Order is “Evaporator Temperature Order 3". The value of the three temperature orders must be set according to the appliance and the desired cabinet temperature for each operation point (Low, Medium or High).
Figure 10. Temperature control tab
3.5.2 Timing control
parameters are sent and received by clicking on “Set” or “Get” buttons, respectively. Figure 11. Timing control tab zero voltage by MCU in order to synchronize the MCU orders with the AC mains voltage.
negative cycle (see Figure 12). Figure 12. Gate current pulses
3.5.3 Force debug
- Clicking the “Compressor” button will turn on Q1, and then the compressor is running.
- Clicking the “Bulb” button will turn on Q2, and then the light bulb is lit.
- Clicking the “Defrost” button will turn on Q3, and then the defrost resistor is heating. Note: 1 The Defrost and Compressor cannot be switched ON at the same time. Setting Defrost resets Compressor, and vice-versa. 2 In order to return to “Normal” mode, click the “Debug Mode” button. In this case, all the green lights turn off.
Figure 13. Force debug tab
3.5.4 Parameter measurements
refer to the “Help” menu of the GUI software. samples acquisition error occurred.
4 Conclusion
This document will help cold-appliance designers to use our STEVAL-IHT001V1 thermostat kit to:
- Check the immunity of this ST solution
- Easily check the efficiency gains by hysteresis threshold reduction
- Define the better management of the defrost cycles to improve the overall efficiency
- Adapt the software and hardware for other dedicated designs (different compressors, potentiometer control, added loads, etc.)
UM0277 Thermal sensor linearization Appendix A Thermal sensor linearization An NTC thermistor is a thermal resistor whose value decreases when its temperature increases. The thermal law is exponential, as presented in Equation 1. Equation 1 To achieve a simple voltage sensor, it is better to linearize the temperature response using a constant resistor (R12) added in series with the NTC. A voltage divider is then achieved. The voltage across R12 will follow the supply voltage (Vdd) according to the relationship below: Equation 2 To make the relationship of Equation 2 to vary linearly, it's enough to ensure that the second order derivative will be zero. Equation 3 gives the R12 value to ensure this condition. Equation 3 To linearize the voltage response of a M2020 5 k NTC thermistor from EPCOS, between -20 and +5 °C, a 30 kOhm resistor should be chosen for R12. In this temperature range, Vs varies according to Equation 4, for a 5 V supply: Equation 4 Figure 14 gives the variation of Vs and the linear value given by Equation 4 (Vl), versus the temperature sensed by the NTC thermistor. Rc T() Ro B 1 T--- 1 ⎛⎞• Vs Rc T() R12 2 d ⎛⎞ 2 Vl T() T 51.84+
Figure 14. Linear voltage response of the NTC thermistor (for a 5V supply)
Figure 17. STEVAL-IHT001V1 evaluation board schematic diagram
Table 5. Bill of materials
Table 5. Bill of materials (continued)
- Thermostat Board, loads and mains wires are placed 10 cm above the ground reference.
- The mains wire is shorter than 1m.
- The compressor protective earth is linked to the PE of the board through a 30cm cable.
Figure 18. EN61000-4-4 test layout capability of our generator) depending on the coupling mode (to L, N, PE, etc.).
Table 6. PC interface parameters description
frequency values used in different countries. voltage) output DC current capabilities are included for information. Table 7. C3 capacitor value according to the country
Revision history
Table 8. Document revision history 28-Aug-2006 1 Initial release.