# Questions tagged [thermal]

Relating to temperature rise, the flow of heat, or cooling of components

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### Can I use a brushed DC motor at higher-than-rated duty cycle at reduced load?

I have a linear actuator powered by a brushed DC motor which I got from an adjustable bed. The actuator label has the following information: Input Voltage: 24V DC Max Load: 6000N (Push) Speed: 4.2mm/...
32 views

### Calculating noise of two resistors in series when one of the resistors has a significant flicker noise component

Two resistors are in series like a voltage divider. One resistor is a very large Vishay TNPW series with no excess noise. Excess noise is defined as noise in excess of the thermal noise due to current ...
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84 views

### Proof showing thermal noise of 2 resistors in series behave as a single noisy resistor

For the second part of this question, I came up with two slightly different answers? I believe it's the second one however I am not too sure which one would be the correct one. First one: Second one: ...
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18 views

### Thermal fuse replacement

I need to replace a failed thermal fuse, but I cannot match a replacement exactly. I need a ShengPing SPF70-73C, TH=45C, TM=115C/10a @ 250v. How close do I have to match these specs, over and/or ...
1 vote
57 views

### How does Cu plane thickness really matter for PCB heat flow?

This is a follow up question to an earlier one. If we trace the heat flow, the real bottle neck is the thermal impdeance between PCB surface and ambient air. As long as you dont work around that, ...
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### How to best relate a case temperature measurement with the actual junction temperature?

If I have 4W of power dissipated through a transistor (as derived from measured current and the datasheet's on-resistance) and I measure 40 deg. C on the case of the transistor, what is the best way ...
• 713
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### How to remove an old epoxy-like thermoconductive compound?

I'm not sure if this is the place to ask or it would be better suited for retrocomputing. I'm salvaging some old components from old boards and I came across a very hard blue thermal compound that a ...
1 vote
68 views

### What's the purpose of a large thermal pad without a heatsink?

I found this thermal pad on a controller board for SATA to USB enclosure. It's stuck on the SATA to USB bridge ICs. You can see 2 ICs to the left of it. There was an identical thermal pad adhered ...
58 views

### Protecting a soldering hot plate with thermal fuse

I am DIYing a reflow soldering hot plate, with an SSR allowing to regulate the hot plate temperature. However, I understand that SSRs can sometimes fail closed, which basically means that this would ...
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46 views

### Lumped parameter thermal network model of a motor (LPTN)

I'm interested in designing a lumped parameter thermal network model for an electrical motor, in order to estimate the motor coil's temperature during transients. I know that a simple first order ...
30 views

### Can I treat the thermal shock test temperature as the continuous operating temperature of a conformal coating?

We are using this conformal coating on our design, HumiSeal 1B73EPA. However, it does not state in the datasheet the continuous operating temperature for the coating, only the thermal shock test ...
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### Is the difference in thermal resistance for putting a thermal plane on the outer layer vs an inner layer really only like 10%?

In MOSFET datasheets you often see something like junction to ambient thermal resistance of 40K/W being achieved using a 1" x 1" pad on the drain. The main problem with this approach is ...
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### SOA Mosfet Confusion

I am using mosfet (IRHJ9A7234) as a load switch and Id current is about 0.7A and maximum Rds from datasheet is 110mohm. So I thought based on power calculation P= I^2*R = 77mW which is way below than ...
1 vote
109 views

### how to make heat sink under heat pads in kicad 7

Retired user here that have not designed a circuit in the last 3 years. So I got myself KiCad 7 and boy oh boy things have changed! Mostly for the better, but some things I used to do are now a real ...
1 vote
36 views

### Thermal EMF on shunts

I tested the accuracy of a shunt resistor of 20 μΩ by applying short pulses of 100 A. At lower current levels near 0, I noticed the sensed current had a variation of ±300 mA. I did some research and ...
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1 vote
63 views

### IC thermal pad: Place heat sink directly over bottom-side thermal pad and thermal vias

If a VQFN package (below) has a thermal pad and thermal vias beneath it, the bottom layer should have an identical pad to act as a heat sink. Is it typical to surface mount a heatsink on the bottom-...
• 437
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### IC thermal pad: Duplicate zone in inner layers also?

Question For a passively-cooled portable device (fanless, ambient cooling), what are typical methods to supplement the thermal pad of an IC to mitigate device temperature rise, (beyond efficient ...
• 437
84 views

### Current and voltage, thermal flashers (bimetallic blinkers)

I am looking for voltage vs time and current vs time plots at the load side for an automotive old time turn signal blinker in series with a switch and a standard 21 W incandescent light bulb. I was ...
• 1,061
149 views

### How can I measure the internal resistance of a thermoelectric generator?

How can I measure the internal resistance of a thermoelectric generator? Can I use a standard multimeter? I am using a TEC1-12706B thermoelectric generator. I tried to use a standard multimeter to ...
761 views

### Thermal conductivity of 1600W/m·K?

I am comparing different thermal conductivities in the market and found that the thermal conductivity goes up to 1600W/m·K for a thermal sheet, but a thermal paste is still 0.65 W/m·K. Does it make a ...
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407 views

### Mounting an 11W SCR with a Flat Profile

I have two SCRs in my design that will be switching up to 15A at 120-240VAC. The two devices will split the power, with each one conducting a half cycle. I'm considering using the S6025 by Littelfuse. ...
• 101
553 views

### PCB as heat sink - how to calculate the area

I got an Inverter of 6 MOSFETs and I need to estimate the PCB area for keeping the junction temperature below 100 °C. The losses per FET are 0.21 W which leads to a max. Rthja = 143 K/W (junction to ...
• 147
73 views

### Estimating GaN HEMT junction temperature

I think it's quite a simple question, but the solution is not so obvious for me. I know the equation Tj=Ptot×Rth+Ta, the thermal resistance Rthj-a and RDSon temperature dependance come from the ...
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900 views

### 8.3 kW DC brushed motor controller thermal management

I'm designing a brushed DC motor controller for an 8.3 kW, 24 V, 350 A forklift motor. I will be controlling only one direction so I'm using a 70 kHz PWM from an MCU. The circuit will be a push-pull ...
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1 vote
74 views

### How to derive thermal time constant from a MOSFET's datasheet?

I use the Vishay SiA440DJ MOSFET in a PMSM inverter. For thermal simulation in Maltab/Simscape I need to provide thermal data. On pg. 1 of the datasheet the thermal resistance Junction to ambient = 80 ...
• 147
755 views

### How much power in an IC to feel hot

Is there any rule of the thumb at which power dissipated in an IC one should be able to feel that it is hotter than the other components? More specifically, I have a "signal" that should ...
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1 vote
75 views

### Difference between Kelvin and Celsius in dynamic thermal behavior of MOSFETs

I am trying to understand the temperature behavior at the junction level and this Application Note "AN_201712_PL11_001" from Infineon describes the process. The problem is that I have a hard ...
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1 vote
81 views

### Is it possible to multiplex thermistors for multiple cell battery configurations for the BQ25756 or other JEITA charge ICs for spaced apart cells?

I'm trying to figure out how to safely implement fast charging using the BQ25756 with a most likely 2s (though up to 4s is possible) layout of physically spaced out cells. I haven't fully decided on ...
115 views

### Understanding thermal instability breakdown in pn junctions

I am currently reading Sze (Physics of Semiconductor Devices, 3e, Chapter 2.4.1) and am trying to understand his discussion of thermal instability breakdown/runaway in pn junctions. I have also ...
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1 vote
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### PMV20XNER MOSFET Overheating

I am using the PMV20XNER as a simple switch. I am driving a load of about 8 Ω from a 24 V power supply. A schematic is below: When I apply 3.3 V to the gate (which should be enough to turn this ...
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1 vote
139 views

### Would a PCB thermo handle a high power LED?

I need to have my Cree T6 5 W LED on the star, on top of my Arduino shield, would that resist the LED heat? I plan to use thermal adhesive and custom make my shield so is 2 sided, with thermal vias ...
• 1,057
1 vote
109 views

### Calculating Case-to-Sink thermal resistance from bulk thermal conductivity of thermal pad material

I am using a thermal pad instead of a thermal compound between the mosfet and the heatsink. Thermal pad (p/n 53-78-1ACG) has a thermal conductivity of 0.9 W/(m-C) and 0.15mm thickness. Normally I am ...
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2k views

### Thermal relief for a chip without metal plate on the bottom

I have a chip in which I have selected this footprint: Package_SO: SOIC-8_3.9X4.9mm_P1.27mm. This is what it looks like: Because this chip gets pretty hot, I ...
• 1,369
1 vote
368 views

### What is the general rule for LDO thermal considerations at various voltages?

This question isn't so much about my specific case, but rather, I'm looking for a general rule for estimating the max current that can be pulled from heatsink-less LDOs at some voltage difference. I ...
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1k views

### Implementing a 5 Watt, Linear Variable DC Power Supply that DOESN'T get burning hot?

The load I am trying to drive is a fan module that includes a DC cooling fan, a tachometer, some status LEDs and other temperature monitoring electronics. Historically users have swapped power ...
• 131
36 views

### Noise floor of an unmatched resistive network thru PSD calculations

I am modeling the PSD of various loads to calculate noise floors. I have various load terminations from 25 ohms to 250 ohms. Per Johnson-Nyquist, the noise floor on a resistor when load and source are ...
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1 vote
86 views

### Thermodynamics of a simple electrical conductor

I derived an expression for the time constant of the temperature of an electrical conductor and was looking for some constructive feedback. Initially there is no current flowing through the conductor ...
1k views

### What is the most common electronics IC package material?

I'm trying to make a thermal simulation of a PCB, and one of the parameters I have to put in the simulation software is the component package material. For most standard ICs as far as I know, it's ...
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38 views

### Thermal analysis of a step down regulator

LTM8053 datasheet I tried to plot the thermal graphic (watt-celcius) for this buck converter in MATLAB. The main goal is to find losses which turn into heat. Reasons for heat most of time switching ...
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824 views

### Entire FPGA getting hot evenly, not just a single hot spot

I have a board with an Altera EPF10K30RC240-4N that is not functioning at all. There is a high current draw on the board. The +5V rail is only 2.6V and there is 4.2 ohms between +5V and GND. The board ...
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3k views

### Entire Perimeter of FPGA Getting Hot - Why?

I have a commercially-produced board with an Altera EPF10K30-series FPGA. There is an abnormally high current draw on the board. Where +5V should be present, there is only +2.6V. When comparing ...
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75 views

### I'm confused about boundary conditions and walls in thermal simulation (using IcePak)

I'm trying to learn a little thermal simulation. I just have a single LED on a board, I made a 3d model for it. And I thought I could use thermal simulation to see how big I need to make the board to ...
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1k views

### Kicad 7 - Drill out of range

I had a footprint for a component in Kicad 5. Then i updated to Kicad 7 and I am getting this error: ...
• 1,369
1 vote
118 views

### Compensating for lack of via-in-pad for buck converter thermal design

I am designing a buck converter, based on a TI chip. Both the datasheet and an excellent document "Five steps to a great PCB layout for a step-down converter" show vias in the exposed pad, ...
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27 views

### Thermal Conductance of a Pyroelectric sensor

For some temperature changes, I want to use a pyroelectric sensor. I have been looking for the R.G. Whatmore's papers for the basic theory. In the paper, for calculating the time constant. He ...
56 views

### Eagle: Adding thermal to QFN components

How to properly place thermal vias under components? I hook them up to the ground net, the same as the ground pad of my QFN component, but they don't seem to connect. Do I need to edit the footprint ...
1 vote
90 views

### Coupling heatsink RC network to MOSFET's Cauer circuit

I am trying to understand simple RC thermal simulation to analyse the temperature rise in Rohm a 1200 V N-channel SiC MOSFET SCT3040KR. RC Cauer parameters are as depicted in the LTspice circuit ...
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### Do I need to apply thermal relief on the 3V3 polygon?

Should I enable thermal relief for the 3V3 (yellow line) polygon? If not, does it imply that the components on the right-hand side will be more difficult to solder due to their connection to a larger ...
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1 vote