Questions tagged [power-dissipation]

Anything related to power dissipation in electrical and electronic circuits and components, i.e. the process in which electrical energy is converted to heat when current flows through them.

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25
votes
3answers
9k views

How are LEDs considered efficient?

I've always found circuits containing LEDs hard to understand, please bear with me. I know most people find it easy, but I'm confused by them so some of my assumptions might not be correct, please ...
21
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2answers
107k views

Is it possible to calculate how much heat dissipation and temperature rise will take place in a resistor

Suppose I have a 100 mAh battery at 20V. I connect a 1000 kohm resistor across it. How much heat will be generated and how can I find the temperature rise in the resistor? As the battery operates I ...
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 ...
17
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4answers
2k views

125 mW resistor subjected to 600 mW dissipation in professional safety system

The schematic below is the input circuit of a signalling PCB, which we buy from one of our suppliers of fire detection systems. Said PCB has to be built into a so called geographic evacuation panel ...
14
votes
2answers
1k views

How does static dissipative foam work?

I am planning to build a grip-release sensor using the foam. I'm pretty interested in the way it works. Does the resistance in circuit increase or decrease when force is applied onto it? And this will ...
12
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4answers
5k views

LED strips: 46% resistive losses?

I recently bought these LED strips. They are supposed to run on 12V/72W and have 300 x the SMD 5050 LEDs on it. Schematic: simulate this circuit – Schematic created using CircuitLab The ...
11
votes
5answers
4k 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 ...
11
votes
1answer
12k views

How to choose correct resistor with proper wattage and ohms for 6 leds connected in a serial circuit?

Let's suppose I've six LED lights with each 3.2 Volt and 20mA and all six of them are connected in one serial circuit. I know there is better setup but for this I'm using this circuit setup. I'm ...
11
votes
3answers
10k views

Is there any pattern or standard to through-hole resistor sizes?

I've long been under the impression that a quarter-watt resistor has a standard package, and a half-watt resistor has a standard package, etc. But I've recently gotten through-hole resistors which are ...
10
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4answers
4k views

What is making my DC/DC converter's capacitor to blow up?

I'm having some capacitors blown up and I am not sure what's the cause of this. It is definitely NOT OVERVOLTAGE and NOT in WRONG POLARIZATION. Let me introduce the scenario: I have designed a double ...
9
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2answers
3k views

BJT power dissipation - Which value to use? (Ta vs Tc)

I'm using a TIP120 (Darlington pair BJT) brought to saturation for a project of mine. I have \$V_{CE(sat)}=1V\$, \$I_C=2A\$, \$V_{BE}=2.5V\$ and \$I_B=0.005\$A, which give me a total power dissipation ...
9
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3answers
3k views

PCB layout for high side switch (high current)

I'm working on a PCB layout for two high side switches. You can see below a picture of my current layout. The copper weight of the future PCB will probably be 2 oz/ft² (double sided). I use two p-...
8
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1answer
20k views

Wattage calculation for resistors in series

I need the formula for calculating resistor wattage when the resistors are in series. For example, say I have 3 1/4 watt 10 ohm resistors in series. What is the potential power dissipation for the ...
8
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3answers
3k 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 ...
7
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2answers
3k 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 ...
7
votes
1answer
545 views

At the microscopic level, what exactly forces us into the “dark silicon” (i.e., the mismatch between transistor scaling and voltage scaling) problem?

I've read that if you fix the TDP of a chip, you cannot use all of the transistors simultaneously any longer. This leads me to believe that each transistor requires the same power as in previous nodes ...
6
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3answers
8k 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 \$...
6
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1answer
2k views

Is CPU/GPGPU heat dissipation quadratic in clock frequency?

In the following article on overclocking a Pentium from 1GHz to 5GHz using liquid nitrogen: The 5GHz Project, there is an assertion that "Heat dissipation rises exponentially during extreme ...
5
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2answers
5k views

Understanding power dissipation of a diode in a datasheet chart

According to this chart of a diode's power dissipation over temperature, the power dissipation would decrease as temperature goes up. But wouldn't it be the exact opposite and even more power be ...
5
votes
3answers
5k views

Heat dissipation through ground plane and other thermal considerations for 3W LED

In designing my first PCB ever to mount a 3W white led (shown above) thermal dissipation is a concern. It is a simple PCB and I don't have the ability to add any heat sink beyond the ground plane of ...
5
votes
2answers
284 views

5V Regulator Power Dissipation

I am using a 5V regulator (LP2950) from ON Semiconductor. I am using this for USB power and I'm feeding in 9V from an adapter. USB requires maximum of 500mA right? So the maximum power dissipation in ...
4
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5answers
1k views

Transistor power dissipation rating

I'm trying to build the following circuit Except mine is a 24V ~20A (500W) motor, so I need to swap the components. I'm currently looking into transistors and I've stopped on the 2N6284 (NPN) ...
4
votes
3answers
3k views

Can a soapbox-sized device dissipate 10-15W of heat? If yes, how?

Some time ago, I built a soapbox-sized battery testing device. One of its functions was to discharge batteries at a specified current, and it handled most of the common battery sizes well, but its ...
4
votes
2answers
316 views

Overheating Problem?

I have almost no electrical experience, so I apologize about the simplicity of the question in advance. I have 4 resistors a diode and a transistor in a 22mm x 14mm x 8mm enclosure. My concern is that ...
4
votes
1answer
2k views

Vias under thermal pads

I'm working on a design with MOSFETs and with the LT4415 device. The MOSFETs should dissipate an average heat of 0.45 W (with peak at 2 W but just a couple of seconds with several minutes to recover)...
4
votes
2answers
131 views

POWER MOSFET - Thermal Design

i have some doubts about with this thermal design? first, the calculations and infos: My load (a motor) uses an average current of 7A, I could not measure the current peak at the beginning of the ...
3
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2answers
16k views

MOSFET: how to determine if a heatsink is required? [closed]

for a given mosfet, how do I know how much current can it handle without a heatsink? I could just play it safe and add a heatsink + fan but the controller board am using doesn't have mounting holes ...
3
votes
3answers
631 views

Is “switching frequency” measured for a full cycle or half cycles

Here's a sample datasheet from a FET driver: http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=ucc27211a&fileType=pdf Section 9.2.2.5 describes calculating power dissipation....
3
votes
2answers
193 views

Calculate voltage drop across Linear MOSFET in saturation region

Considering the below schematic, how is the voltage drop across the MOSFET calculated when it is operated in the saturation region? I am trying to calculate the power dissipated by the MOSFET so that ...
3
votes
1answer
1k views

Why is this switching transistor heating up?

I am building control board for fan cooling. It runs from 12V power source, and it is controlled by input analog signal 0.3V to 1.2V which just controls speed of fan. Problem is that switching ...
3
votes
1answer
106 views

Help understanding why heat sinks work

Okay, so I'm trying to figure out why use heat sinks at all. Let's say if have a component that, by itself, is trying to dissipate (PD) 11W of power. The current TJ is at 50°C and the RJ-A of the ...
3
votes
2answers
97 views

How to be sure that a ceramic capacitor can manage a RMS current?

I'm in the middle of a design and I need a capacitor of: 10µF Rated at 10V Has to handle a ripple current of 250mA RMS, at 400kHz Most electrolytic capacitor data sheets give a maximum RMS value for ...
3
votes
1answer
794 views

N Mosfet with 8 pinout

I was wondering why some MOSFET transistors like This one has 8 pinout instead of 3 ?
3
votes
2answers
824 views

Precautions needed to parallel P-MOSFETs as high side load switches?

I plan to use P-MOSFETs (SI7463) as high side load switches, with a slight soft-start (to be tested and tweaked after PCBs are made). I'd like to parallel them in order to make the equivalent Rds-on ...
3
votes
2answers
623 views

SOA analysis for MOSFET-based Electronic Load

I'm working on a second-generation design for an electronic load. The first generation is described in this prior question if anyone is interested (scroll down to section containing first photo), but ...
3
votes
2answers
337 views

Heat dissipation in a DIP Solid State Relay

I am working on an application that switches a high power (15 W typical, 100 W maximum) resistive load at 230 VAC (RMS) from a 5 VDC control line. For this I plan to use a Solid State Relay. I am ...
2
votes
1answer
1k views

Smoking Transistor in Low-Side Switch. What Am I Doing Wrong?

I have some of these (RGB LEDs with drivers). They connect to 12V, and they draw a max of 1.8A total (full white): I wanted to add a low-side switch to turn the load on/off via a PIC I/O pin output. ...
2
votes
2answers
2k views

Would replacing a resistor by another one of identical value but higher power rating affect the working of a circuit?

The schematic recommends using 20 Ω 1W as collector resistance. What I have at hand are two 10 Ω rated for 10W. I'm guessing the change should be acceptable ... What difference would it ...
2
votes
3answers
116 views

Power supply design for CPU: Define maximum current needed

This is something that is troubling me in many of my projects and I would like to know if there is any standard approach to it. The question is how should I correctly design / dimension my power ...
2
votes
2answers
8k views

How to calculate a circuits efficiency with the help of LTspice

Note that this is not a question for circuit critique (and lots of things could be said about this circuit) but this circuit is only the base for the discussion of further points. Here it is (an ...
2
votes
1answer
845 views

Energy dissipation in RC circuit given AC sinewave input

I'm implementing a low-pass RC circuit that as an input will have an AC sine wave voltage input. How can I calculate the average power dissipation in the resistor, given R, C, peak (or RMS) voltage ...
2
votes
1answer
2k views

Is this the correct way to calculate IGBT power loss?

I am having trouble obtaining the power dissipation of IGBTs. It does not have a buit in diode and it isn't driving an inductive load. So I read in an application note that IGBT power losses are ...
2
votes
1answer
59 views

Power dissipation calculation for FPGA-ADC interface

An FPGA can be interfaced with an ADC using CMOS or LVDS. Is there a way to use simulation to predict the power dissipation of the I/O blocks for a given operating frequency for this interface? If so, ...
2
votes
2answers
170 views

Extruded heatsink question

I have few questions about a general extruded heatsink. As example, we can use this from Farnell. Let's say it is long 20cm with a given shape, sold to have a Thermal resistance of 10°C/W. Q1: (...
2
votes
1answer
433 views

One MOSFET appears to get hotter than the other

I am trying to figure out some sources of error in this circuit. Firstly, the lower FET (in the schematic) seems to dissipate more power and heat up faster than the top FET. The shcematic above ...
2
votes
5answers
589 views

How to decide dimensions of PCB heatsink?

I am using MCP73213 IC for charging my 2S Li Ion battery. I want to use this IC for 1 ampere charging during constant current charge cycle. My specifications are as follows. Input source voltage : ...
2
votes
5answers
2k views

Power dissipation in resistor from triangle wave

How to calculate power dissipation through resistor from specific wave form? Wave: Triangle, 1V, 1kHz Resistor: 10kohm Q: What is the power dissipation in the resistor, considering frequencies up ...
2
votes
1answer
2k views

Output power vs idle power of an audio amplifier

Let's say I have a AB class power amplifier that is able to give an average output power of 30W on a 6 ohm loudspeaker. Now in ...
2
votes
1answer
633 views

Is 150mW a lot to dissipate from a TO-92 in 50°C free air without heat sink?

I'm designing a circuit in which a 2N3096 PNP BJT in a TO-92 package will drop 15V with \$I_C\$ of 10mA worst case, for 150mW heat dissipation. Unfortunately, the worst case is when the circuit is ...
2
votes
1answer
1k views

Alternative to high Watt resistor terminating resistor

In the following circuit a 120 ohm termination resistor is placed across the Rx+ and Rx- data lines connected to a RS485/422 transceiver. The transceiver is protected up +/- 60V. simulate this ...