electro-thermal | PartQuest™ Explore

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Designer

Description

This example shows the importance of modeling thermal interaction effects, or "thermal crosstalk", in power dissipating circuits. The "design" is a simple transistor amplifier, using just an 8 Ohm pull-up resistor and an active pull-down NPN BJT. Both of these models are from our "Thermal and Electro-thermal" Components Library, so they have a thermal port that can connect to an external thermal network. These models output all power dissipated in the device as a thermal heat-flow into that network.

The thermal network includes the heat-sink's heat capacitance (0.1 J/degC) and heat transfer resistance to the ambient (10 degC/Watt). This assumes the resistor and transistor contribute heat to the same heat-sink. The transistor's thermal heat-flow path also includes an 8.8 degC/Watt resistance, to represent the Junction-to-Lead Thermal Resistance as published in the device datasheet (Diodes Inc. FZT869).

From the simulation results it is clear that the heat-sink temperature rises to nearly 120 degC (purple waveform), causing the transistor's junction temperature to approach 150 degC (average, red waveform). This is significantly higher than the value predicted in the companion design example: "Modeling Transistor Amplifier Self-Heating - Hot Part Monitor", which assumed the two devices were thermally isolated.

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Copy of Thermal Modeling of AC-DC Power Adapter With Current Boost Regulator - on Sat, 08/26/2023 - 07:03

Designer

Description

This example shows the capability of modeling the electrothermal aspects of power dissipating circuits. The design is a 5V regulator (non-switching), driven from a 120 Vac/60 Hz input and using a transformer/rectifier circuit to step down to a much lower DC-link voltage.

The load current capability is 5A, which is well above the current limit of the linear regular component itself. This is thanks to the load sharing role of the bypass PNP transistor. The design is based on an example application circuit shown in Figure 11 of the On Semiconductor Datasheet MC7800/D, November 2014 - Rev. 27.

All of the power dissipating electronics' models are from the "Thermal and Electro-thermal" Components Library. They have a thermal port that connects to the thermal network (i.e. red wires). These models output all the power dissipated in the device as a thermal heat-flow into that network. This includes the rectifier diodes, the linear regulator and the BJT, as well as the current sense resistor and the effective winding resistances of the transformer primary and secondary.

The thermal network includes the heat-sink's heat capacitance (0.1 J/degC) and heat transfer resistance to the ambient (1 degC/Watt), as well as the datasheet published values for the junction-to-lead thermal resistances of all the active electronic components. An assumed value for the thermal capacitance of the BJT (0.005 J/degC, not provided by the manufacturer) was added for purposes of illustration. Obtaining the actual value would require deeper analysis or measurement of this important component characteristic. However, in this example, both thermal capacitance values were selected solely to give sufficiently fast thermal time constants, so that steady-state operating temperatures could be reached with minimal simulation time.

This design is based on another shared design:

"https://www.systemvision.com/design/ac-dc-power-adapter-current-boost-regulator", That design has been modified not only to add the electrothermal aspects, but it was also adjusted to improve its observed thermal performance. For example, the DC-link capacitance (c3) was increased from 4700uF to 22000uF, to allow a reduced DC-link operating voltage (i.e. to improve efficiency) while avoiding regulation drop-out at AC zero-crossings under heavy load conditions.

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Copy of Electro-thermal Trade-off Analysis for AC-DC Converter with Current Boost Regulator - on Sat, 07/15/2023 - 16:15

Designer

Description

This example shows the capability of modeling the electrothermal aspects of power dissipating circuits. The design is a 5V regulator (non-switching), driven from a 120 Vac/60 Hz input and using a transformer/rectifier circuit to step down to a much lower DC-link voltage.

The load current capability is 5A, which is well above the current limit of the linear regular component itself. This is thanks to the load sharing role of the bypass PNP transistor. The design is based on an example application circuit shown in Figure 11 of the On Semiconductor Datasheet MC7800/D, November 2014 - Rev. 27.

All of the power dissipating electronics' models are from the "Thermal and Electro-thermal" Components Library. They have a thermal port that connects to the thermal network (i.e. red wires). These models output all the power dissipated in the device as a thermal heat-flow into that network. This includes the rectifier diodes, the linear regulator and the BJT, as well as the current sense resistor and the effective winding resistances of the transformer primary and secondary.

The thermal network includes the heat-sink's heat capacitance (0.1 J/degC) and heat transfer resistance to the ambient (1 degC/Watt), as well as the datasheet published values for the junction-to-lead thermal resistances of all the active electronic components. An assumed value for the thermal capacitance of the BJT (0.005 J/degC, not provided by the manufacturer) was added for purposes of illustration. Obtaining the actual value would require deeper analysis or measurement of this important component characteristic. However, in this example, both thermal capacitance values were selected solely to give sufficiently fast thermal time constants, so that steady-state operating temperatures could be reached with minimal simulation time.

This design is based on another shared design:

"https://www.systemvision.com/design/ac-dc-power-adapter-current-boost-regulator", That design has been modified not only to add the electrothermal aspects, but it was also adjusted to improve its observed thermal performance. For example, the DC-link capacitance (c3) was increased from 4700uF to 22000uF, to allow a reduced DC-link operating voltage (i.e. to improve efficiency) while avoiding regulation drop-out at AC zero-crossings under heavy load conditions.

About text formats

Copy of Electro-thermal Trade-off Analysis for AC-DC Converter with Current Boost Regulator - on Wed, 03/10/2021 - 17:42

Designer

Description

This example shows the capability of modeling the electrothermal aspects of power dissipating circuits. The design is a 5V regulator (non-switching), driven from a 120 Vac/60 Hz input and using a transformer/rectifier circuit to step down to a much lower DC-link voltage.

The load current capability is 5A, which is well above the current limit of the linear regular component itself. This is thanks to the load sharing role of the bypass PNP transistor. The design is based on an example application circuit shown in Figure 11 of the On Semiconductor Datasheet MC7800/D, November 2014 - Rev. 27.

All of the power dissipating electronics' models are from the "Thermal and Electro-thermal" Components Library. They have a thermal port that connects to the thermal network (i.e. red wires). These models output all the power dissipated in the device as a thermal heat-flow into that network. This includes the rectifier diodes, the linear regulator and the BJT, as well as the current sense resistor and the effective winding resistances of the transformer primary and secondary.

The thermal network includes the heat-sink's heat capacitance (0.1 J/degC) and heat transfer resistance to the ambient (1 degC/Watt), as well as the datasheet published values for the junction-to-lead thermal resistances of all the active electronic components. An assumed value for the thermal capacitance of the BJT (0.005 J/degC, not provided by the manufacturer) was added for purposes of illustration. Obtaining the actual value would require deeper analysis or measurement of this important component characteristic. However, in this example, both thermal capacitance values were selected solely to give sufficiently fast thermal time constants, so that steady-state operating temperatures could be reached with minimal simulation time.

This design is based on another shared design:

"https://www.systemvision.com/design/ac-dc-power-adapter-current-boost-regulator", That design has been modified not only to add the electrothermal aspects, but it was also adjusted to improve its observed thermal performance. For example, the DC-link capacitance (c3) was increased from 4700uF to 22000uF, to allow a reduced DC-link operating voltage (i.e. to improve efficiency) while avoiding regulation drop-out at AC zero-crossings under heavy load conditions.

About text formats

Copy of Electro-thermal Trade-off Analysis for AC-DC Converter with Current Boost Regulator - on Wed, 03/10/2021 - 17:42

Designer

Description

This example shows the capability of modeling the electrothermal aspects of power dissipating circuits. The design is a 5V regulator (non-switching), driven from a 120 Vac/60 Hz input and using a transformer/rectifier circuit to step down to a much lower DC-link voltage.

The load current capability is 5A, which is well above the current limit of the linear regular component itself. This is thanks to the load sharing role of the bypass PNP transistor. The design is based on an example application circuit shown in Figure 11 of the On Semiconductor Datasheet MC7800/D, November 2014 - Rev. 27.

All of the power dissipating electronics' models are from the "Thermal and Electro-thermal" Components Library. They have a thermal port that connects to the thermal network (i.e. red wires). These models output all the power dissipated in the device as a thermal heat-flow into that network. This includes the rectifier diodes, the linear regulator and the BJT, as well as the current sense resistor and the effective winding resistances of the transformer primary and secondary.

The thermal network includes the heat-sink's heat capacitance (0.1 J/degC) and heat transfer resistance to the ambient (1 degC/Watt), as well as the datasheet published values for the junction-to-lead thermal resistances of all the active electronic components. An assumed value for the thermal capacitance of the BJT (0.005 J/degC, not provided by the manufacturer) was added for purposes of illustration. Obtaining the actual value would require deeper analysis or measurement of this important component characteristic. However, in this example, both thermal capacitance values were selected solely to give sufficiently fast thermal time constants, so that steady-state operating temperatures could be reached with minimal simulation time.

This design is based on another shared design:

"https://www.systemvision.com/design/ac-dc-power-adapter-current-boost-regulator", That design has been modified not only to add the electrothermal aspects, but it was also adjusted to improve its observed thermal performance. For example, the DC-link capacitance (c3) was increased from 4700uF to 22000uF, to allow a reduced DC-link operating voltage (i.e. to improve efficiency) while avoiding regulation drop-out at AC zero-crossings under heavy load conditions.

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tunable example 2

Designer

Description

This LED lighting example demonstrates the value of simulating both the electrical and thermal* aspects of power dissipating circuits together, simultaneously.

In this application example, a Vishay NTCS0603 Thermistor provides feedback of the enclosure temperature. This feedback is used to control PWM dimming of the LEDs, thereby limiting the internal temperature when operating at high external ambient temperature conditions.

This is a "Live" design, the user can change key parameter values and then run new simulations to see the results. These parameters include "r_mirror", the resistance of the current mirror that controls the capacitor charging rate of the 555 timer, and thereby set the PWM frequency. The user can also change "r_offset" that controls the temperature level at which the dimming operation begins. Finally, the user can set "r_iLED_set", to control the ON-state operating current of the LEDs.

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* To reduce the time needed to simulate the transition and settling at 6 different temperature levels, all thermal time constants were reduced by approximately 1000x. The actual thermal response time constant of the NTCS0603 is approximately 3 seconds (depends on mounting), not 3 msec! Also, the enclosure thermal capacitance value would more likely be 3 (J/degC) instead of 3 (mJ/degC), giving a thermal time constant for the enclosure of 10 (degC/Watt) * 3 (J/degC) = 30 seconds. This time scaling does not affect the static relationship between the outside temperature and PWM dimming.

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Copy of Modeling Transistor Amplifier Self-Heating - Thermal Network - on Thu, 03/04/2021 - 14:49

Designer

Description

This example shows the importance of modeling thermal interaction effects, or "thermal crosstalk", in power dissipating circuits. The "design" is a simple transistor amplifier, using just an 8 Ohm pull-up resistor and an active pull-down NPN BJT. Both of these models are from our "Thermal and Electro-thermal" Components Library, so they have a thermal port that can connect to an external thermal network. These models output all power dissipated in the device as a thermal heat-flow into that network.

The thermal network includes the heat-sink's heat capacitance (0.1 J/degC) and heat transfer resistance to the ambient (10 degC/Watt). This assumes the resistor and transistor contribute heat to the same heat-sink. The transistor's thermal heat-flow path also includes an 8.8 degC/Watt resistance, to represent the Junction-to-Lead Thermal Resistance as published in the device datasheet (Diodes Inc. FZT869).

From the simulation results it is clear that the heat-sink temperature rises to nearly 120 degC (purple waveform), causing the transistor's junction temperature to approach 150 degC (average, red waveform). This is significantly higher than the value predicted in the companion design example: "Modeling Transistor Amplifier Self-Heating - Hot Part Monitor", which assumed the two devices were thermally isolated.

About text formats

Copy of Coffee Cup Warmer with Thermostat Control - on Sun, 02/28/2021 - 21:31

Designer

Description

This design represents a simple automotive (12V) coffee cup warmer, with digital thermostat. It is not meant to be a practical design, but rather to show some of the capabilities of modeling multi-discipline electro-thermal systems in SystemVision Cloud.

The design includes a "plant" model with both static and dynamic thermal aspects, including a tungsten heater element, conduction and radiation heat transfer, and heat capacitance. A "graphical" model of the temperature sensor includes math function-blocks to set the bandwidth (LPF), gain (sensitivity), offset bias and output voltage limiting. It also includes an output resistance.

The closed loop performance of the system depends on the sensor bandwidth and the sampling rate. Try using 1 Hz instead of 0.1 Hz for the pole frequency "FP" in LPF1, and a 0.2 second period for the sample clock. You'll notice that the faster sensor and sampling greatly improves the temperature regulation.

The thermostat includes a simple amplifier and a single-bit voltage-to-digital converter, with a threshold level that specifies the temperature regulation set-point. A digital clock and D flip-flop sample and preserve the desired state of the heater switch during each clock cycle.

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Copy of Linear Regulator Temperature Finder - on Tue, 01/26/2021 - 15:15

Designer

Description

This "virtual test circuit" can help designers predict the temperatures of a linear regulator, based on readily available information from the manufacturer's datasheet. Users can simply make a copy of this circuit, then adjust the regulator model's parameters to match the electrical and thermal characteristics for their particular part.

These parameters include the output voltage, VDO and current limit, as well as the junction-to-case and junction-to-ambient or heat-sink thermal resistance values. In this example, an L78S05 with direct case to ambient heat transfer is modeled (i.e. no heat-sink). The datasheet specifies the junction-to-case resistance is 5degC/Watt, and the junction-to-ambient resistance for a T0-220 package is 50 degC/Watt. Therefore, the difference of 45 degC/Watt is assumed to be the case-to-ambient thermal resistance. This value is assigned as the "heat-sink" resistance.

If an actual heat sink is being used, its published thermal resistance would be used instead. If the heat sink heat capacitance is also provided, that value can be applied to the thermal capacitor, and then the simulation will predict not only the steady-state operating temperature, but also temperature transients.

The input voltage function generator can also be adjusted to apply any time-varying input voltage profile, and the test circuit will show the corresponding time-varying temperature profile. This can be used to identify peak as well as average operating temperatures.

The user can also change the load current level and/or the load type using any relevant models in the Component Library, or create custom load models.

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Copy of Linear Regulator Temperature Finder - on Tue, 01/26/2021 - 15:15

Designer

Description

This "virtual test circuit" can help designers predict the temperatures of a linear regulator, based on readily available information from the manufacturer's datasheet. Users can simply make a copy of this circuit, then adjust the regulator model's parameters to match the electrical and thermal characteristics for their particular part.

These parameters include the output voltage, VDO and current limit, as well as the junction-to-case and junction-to-ambient or heat-sink thermal resistance values. In this example, an L78S05 with direct case to ambient heat transfer is modeled (i.e. no heat-sink). The datasheet specifies the junction-to-case resistance is 5degC/Watt, and the junction-to-ambient resistance for a T0-220 package is 50 degC/Watt. Therefore, the difference of 45 degC/Watt is assumed to be the case-to-ambient thermal resistance. This value is assigned as the "heat-sink" resistance.

If an actual heat sink is being used, its published thermal resistance would be used instead. If the heat sink heat capacitance is also provided, that value can be applied to the thermal capacitor, and then the simulation will predict not only the steady-state operating temperature, but also temperature transients.

The input voltage function generator can also be adjusted to apply any time-varying input voltage profile, and the test circuit will show the corresponding time-varying temperature profile. This can be used to identify peak as well as average operating temperatures.

The user can also change the load current level and/or the load type using any relevant models in the Component Library, or create custom load models.

About text formats

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