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Questions tagged [thermal]

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

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28
votes
6answers
10k views

Why aren't CPUs cooled from below as well as above?

The transistory bits of an integrated circuit are approximately in the centre of the (plastic or ceramic) package. They sometimes get hot, and we cool them by affixing a heat sink to one side. ...
28
votes
4answers
18k views

How do I determine the area of copper needed on a PCB to provide adequate heatsinking for a power SMD MOSFET?

I am planning to use the IRFR5305PBF Power MOSFET (http://www.irf.com/product-info/datasheets/data/irfr5305pbf.pdf) to switch on a load. I have determined that I need an external heatsink with Rthsa &...
25
votes
7answers
13k views

Optimize heat sink design - connect cooling pad on PCB backside by vias

In one of my current projects I'm using an MC7805 in a D2PAK package to generate my logic supply of 5 V from an available 24 VDC supply. The current required by the circuit is 250 mA. ...
22
votes
8answers
7k views

How to solder a 70 °C (158 °F) thermal / temperature fuse

For my DMX project (schematics is not important), I soldered this temperature fuse which has just two leads (see picture below). The fuse doesn't work (meaning it does not conduct electricity) ... ...
18
votes
3answers
5k views

Why do 0 dB attenuators exist?

I am reading this paper : Upgrade of a low-temperature scanning tunneling microscope for electron-spin resonance and found that for thermalization, they use 0 dB attenuators. Page 6: Having the ...
18
votes
1answer
1k views

TO-92 not getting hot enough

I am controlling a DC fan by an AVR MCU and I am curious about the thermal characteristics of a 2N3904 NPN transistor over which the fan is connected. Reading the transistor's datasheet, I find the ...
16
votes
3answers
43k views

How do filament LED bulbs work, looking very similar to incandescent bulbs?

Filament LED bulbs use very narrow strips containing the LED, which look similar to filaments of an old incandescent bulb: They look like a normal bulb with large "old-style" coal filaments, and are ...
15
votes
8answers
7k views

Why are electrically insulating heatsinks so rare? Is it just cost?

Edit: It seems my initial question (Why are there no insulating heatsinks?) was based on a false premise, and there are in fact insulating heatsinks--I just wasn't able to find them with a cursory ...
15
votes
5answers
2k views

SMD IC mounted upside-down inside a drill hole for extreme low-profile requirements

I don't know if the title is descriptive enough, but I came across this PCB and could stop to wonder about its brilliant design. It is an aftermarket trigger controller for an airsoft gun that works ...
14
votes
9answers
7k views

Does the paint colour matter on a heat sink?

Heat leaves a heat sink via conduction, convection and radiation. I was taught that black surfaces are best at radiating heat and correspondingly a lot of heat sinks are black. But they also have ...
13
votes
2answers
3k views

Is a thermally conductive pad always useful between TO220 and heat-sink?

I have a doubt about heat-sinking that I could not solve by surfing the Web. My doubt arised when mounting a TO220 package on its heat-sink using these dirty cheap pads, but actually it has quite a ...
12
votes
4answers
3k views

What mad solder type is used for BGA?

Having nothing to do in my workshop, I decided to practise my skills a bit. I digged up a scrapped graphics card from the junk box and decided to try to desolder the RAM-chips (BGA) after seeing how "...
12
votes
3answers
9k views

Can an infrared thermometer (IR gun) be used to measure the ambient room temperature?

I know the principle of an IR thermometer, but have one question regarding that are as below. As an IR thermometer senses the radiated IR waves from external bodies coming in their field of view and ...
12
votes
5answers
1k views

Enclosure best air flow profile

I'm in final step of a project an I need some advice about what heat evacuation profile should I use to place three fans for cooling, I have four alternatives as shown in the diagram but I don't know ...
12
votes
2answers
272 views

What is reasoning behind the common wisdom of limiting the temperature rise of a PCB trace to 5/10/20°C?

When deciding on the trace thickness required to carry a certain amount of current on a PCB, the answer depends on how much temperature rise you are willing to accept. This leads the designer into the ...
10
votes
4answers
1k views

Determine whether chassis is a suitable heatsink?

I picked up a sweet little aluminium box for a small USB powered DAC project... ...and while putting it together I noticed the side panels of the box were very cool to the touch, and made of thick ...
10
votes
8answers
2k views

Modelling heat transfer from Power LED to metal bar

I'm playing around with workplace illumination and have developed a 20 V –> 38 V PWM'able constant current source to drive my power LEDs (max power about 64W). So far, so good. However, I've nearly ...
10
votes
1answer
480 views

Purpose of exposed ground pads

I have a Beckhoff EL2008 8-channel digital output terminal that I took apart because I'm using an ASIC that is inside the module, Beckhoff's ET1200. There is essentially a ring of ground pads,some ...
9
votes
5answers
3k views

In a CPU, does the speed of a calculation affect the heat generated?

Take as an example a CPU that is capable of changing its clock speed, like a modern computer CPU (Intel, AMD, whatever). When it does a certain calculation at a particular clock speed, does it ...
8
votes
3answers
1k views

OP1678 running hot

I have built a circuit that converts a 0-5 V signal to a +/- 9 volt signal using OPA1678 Op-Amps (original design from Here). The 0-5V signal is received from a 10k potentiometer across the +5V and ...
8
votes
2answers
1k views

Thermal EMF (seebeck effect) on PCBs

Can poor PCB fabrication process / assembly, and the type of solder used cause thermal EMF (seebeck on PCB) problem? Is it affected by the type of the material used? For example, quality of plating, ...
7
votes
4answers
1k views

Can I create a backside “copper polygon” of the switch node in an SMPS?

I have an SMPS design that has the following properties: 9-15V input voltage 5V, 3A output Switching frequency is 350kHz. Switching controller is a LM25085. The diode used is a DSSK48-003BS. The ...
7
votes
1answer
566 views

How can SCRs be effectively paralleled?

I'm designing a precharge circuit which will carry 200A when closed. I'd like to use MCO150 Silicon Controlled Rectifiers, but they won't handle the current. Two in parallel looks like the most cost-...
7
votes
3answers
181 views

Warming PCB in cold environment using SMD components only

I made a sensor board that needs to operate at about -55 degrees Celcius. Unfortunately, its key component often malfunctions when the circuit is cooled for days at the temperature and then powered up....
6
votes
5answers
2k views

Does this TO-220 Package Resistor need a heatsink?

I purchased this 0.5 Ohm power resistor, which comes in a TO-220 Package, with the aim of pushing 3A through it (i.e. 4.5W) The datasheet has the following information: It says it will rise 6.5 K/W, ...
6
votes
5answers
2k views

How closely should I space my thermal vias?

How closely do you pack your thermal vias? I know that more vias divides the amount of heat each via can move and that smaller vias allows more vias to be packed together. Knowing this, it seems ...
6
votes
2answers
956 views

LM317 - Calculate dissipation due to voltage drop

If I use a linear voltage regulator as LM317: Input voltage = 24 V Output voltage = 5 V (so a voltage drop of 19 V) Mean load = 480 mA (peak load = 700 mA) From the datasheet, I read that maximum ...
6
votes
3answers
758 views

How do electrons carry thermal energy in Peltier coolers?

I've read that when electrons enter from metal to semiconductor type N, they gain thermal energy and make that side cooler and the reverse happens when they leave semiconductor to the conductor. Why ...
6
votes
3answers
5k views

SOT-223 Thermal Pad and Vias

I am using a LDO with a SOT-223 footprint and since it might get hot, I wanted to make a nice thermal pad under it to dissipate that heat. I googled and I only found thermal pads, but i wanted some ...
6
votes
3answers
1k views

Apparent inconsistency of MOSFET power rating in datasheet: SOA v. max power

I am trying to use an IPP114N03L G (datasheet). I calculated the maximum power it could handle as follows: From the first two pages of the datasheet: Rthjc = 3.9K/W Tj(max) = 175C Assuming I can ...
6
votes
2answers
434 views

MOSFET Circuit Design and Thermal Considerations

I'm a newbie at EE, and just I wanted to verify that the design I came up with for a MOSFET circuit that drives a 12V 500mA water pump will work. I'd also like to confirm I can run the N-Channel ...
6
votes
5answers
2k views

Micro-scale solar thermal power

Are there any practical methods of converting solar thermal energy into electrical power on very small scales, eg: using a 300mm diameter paraboloid reflector with temperatures of approximately 800-...
6
votes
3answers
277 views

Heatsink on underside of PCB

I have prototyped some DC-DC converter modules, and they work well. However due to size, I don't have a huge amount of copper pour for them to dissipate their heat. I have used 2oz copper but the ...
6
votes
1answer
932 views

Why do opposing magnetic fields in the same core cause the core to heat up?

I inherited a choke of an odd design, with two windings on the same core. Separately, each winding was about 30 uH. In series, they were about 90 uH. When used in a split-bus boost converter, one ...
6
votes
1answer
1k views

LED module design considerations for an aluminium board

I need to design a LED module something similar to below. Could anyone who is experience tell me if there is any SW (or tools) to determine how to place the LEDs to have a good and evenly distributed ...
6
votes
1answer
1k views

How to correctly apply thermal compound to ICs and heatsinks?

From http://en.wikipedia.org/wiki/Thermal_grease All these compounds conduct heat far better than air, but far worse than metal. They are intended to fill gaps that would otherwise hold air, not to ...
6
votes
1answer
2k views

Generating thermal noise from a resistor

I'd like to create a random number generator based on thermal noise from a resistor, using an opamp to amplify the noise and an inverter to convert the resulting spikes into a digital signal. Here's ...
5
votes
1answer
1k views

If I want to use as little current as possible, then what resistance wire should I use to get the hottest temperature?

I am trying to build a circuit that is able to melt wax (130˚F) and use as few amps as possible since it will need to be powered using a battery. Do I need to be looking for wire that has a high ...
5
votes
5answers
429 views

Is there a design flaw in this voltage regulator application?

I am a veterinarian and I need some help. I purchased two very expensive lift/weigh table/scales. After about 5 years of service one of them failed. I determined that the main PC board had failed. ...
5
votes
2answers
2k views

How to calculate a PNP transistor thermal dissipation?

I am working with a dual power circuit for using USB and a LDO at the same time with a PIC18F2550. The circuit is the same as the one in the PIC's datasheet. My question is: How do I calculate the ...
5
votes
1answer
7k views

What's the difference between a thermal imaging sensor and an infrared CCD?

I was always under the impression that thermal radiation is essentially infrared energy, so what's the difference between a full thermal imaging camera (e.g. an FLIR) and a standard infrared CCD chip? ...
5
votes
3answers
7k views

MOSFET heat calculation question

I am using the FQP30N06L MOSFET: http://www.fairchildsemi.com/ds/FQ/FQP30N06L.pdf. As far as I understand the data sheet, if I connect 5V to the gate and run 2A through drain to source then with a \$...
5
votes
3answers
3k views

What happens with transistor outside max temperature range?

Suppose I have an IGBT transistor rated for 60A, that has junction temperature range of -55 to 175C. What happens if I do not exceed max current, but I do exceed max temperature? The characteristics ...
5
votes
3answers
571 views

Exponential amplifier thermal stabilisation

I am currently trying to build a DIY analog synthesizer. I've looked at a lot of different designs and I am quite stuck on understanding how some exponential amplifier designs work. In analog ...
5
votes
1answer
432 views

Relation between thermal conductivity factor(k) and temperature coefficient of resistance(α)

I'm trying to understand the thermal parameters affecting circuit design. I came across two different parameters. thermal conductivity factor(k) which is related to thermal impedance. The link to the ...
5
votes
1answer
2k views

Thermal pads under IC, how to place vias without soldermask / Decoupling question

I'm looking for a good solution on how to design a thermal pad that is good for solderpaste assembly. PCB fab that I'm using can't place any soldermask on vias like in this example: And I'm not ...
5
votes
2answers
968 views

Experience with thermal glues/adhesives?

I'm planning on using a thermal adhesive to bond an LED pcb to an aluminum enclosure. The enclosure is meant to serve as a heat sink and wick away any heat generated by the LED board. The aluminum ...
5
votes
1answer
235 views

Routing LFPAK MOSFETs

I am routing a PCB with MOSFETs in LFPAK (aka SOT-669, Power SO8) packages for the 1st time. They look like D2PAK. The manufacturer, NXP, advises to draw identical polygons on top and bottom sides, ...
5
votes
1answer
190 views

How does a high voltage condition break down a semiconductor?

I have TVS diode in parallel with circuitry for ESD/lightening/transient voltage protection. Say I receive an over-voltage condition which is beyond the specifications of the part, what happens ...
5
votes
3answers
602 views

Given metal dimensions and material, is it possible to determine the maximum current that the structure can handle? [semiconductor processing]

I have a linewidth structure that has very low resistance. I want to know the maximum current that this structure can handle. Since the resistance of the metal is so low, it's hard to measure the ...