How to smear thermal grease correctly

With the promotion of computer performance, power consumption of CPU is increasing constantly. Due to technology improvement, the power consumption has been alleviated, but because of the enhancement of graphics performance, CPU power consumption is proportional to its performance. Therefore it is still a worthy of our attention that the power consumption is too large to result in higher temperature. Now there has been a very high degree of concern about the heat dissipation problem, however, the majority of consumers simply consider big CPU radiator can solve the dissipation problem. In fact, this idea is very one-side because except for CPU and heat radiator, thermal grease is also very significant and cannot be ignored in the aspects of solving CPU heat dissipation problems.

For many people, thermal grease may not be very striking thing, but it is a very significant link between CPU and radiator. If the way of installing and smearing is not correct, it will lead the temperature of CPU to increase and can even result in the device damage. Thus it is very important to smear thermal grease correctly. There are two main ways, as shown in the following figures: one is that a little grease is squeezed in the center of CPU/GPU surface, and then it is extruded evenly by a radiator; the other one is that the thermal grease is smeared on the surface of CPU/GPU by a finger. The first method is suitable for a relatively small surface area and the second one is more suitable for a larger area.

Fig. 1. The first smear method

Fig. 2. The second smear method

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NTC thermistor (II)

II. The performance of thermistor

With higher and higher precision requirement for temperature measurement and more and more harsh measurement environment requirement, high stability and precision thermistor has been developed and produced. This kind of thermistor has compact size, wide resistance, high precision, and short response time.

III. The development of thermistor

As the thermistor in high temperature application, it shall has the following conditions:

a. Thermistor material is stable; electrode material is stable, with high density, and is connected closely with the lead.

b. Thermal expansivity of the thermistor, the lead and packaging materials match.

c. The lead and packaging material are stable.

d. The packaging material has good insulativity in high temperature.

e. Heat and shock resistance, and reliability.

High precision high stability NTC thermistor is mainly applied for temperature control and measurement for xerographic printer, automation equipment, thermal printing heads, furnace and water heater. In recent years, NTC thermistor has been used in automobile in a new way. It’s used in electronic oil injection system of automobile motor for measuring the temperature of the exhaust gas in order to improve fuel utilization.

To be continued…
A number of thermistors are provided here in ATI.

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NTC thermistor (I)

In industry and agriculture manufacture, national defense, scientific research and office equipment automation fields, temperature is a very critical data. Temperature sensor, i.e. thermistor is a kind of sensor with repeatability and regularity. Among all the temperature sensitive components, thermistor holds a very important position, accounting for 40% of the total temperature sensitive components. According to the characteristics of resistance change with changes in temperature, there are two types of thermistor: NTC thermistor and PTC thermistor. The former resistance decreases when the temperature rises, while the latter resistance increases when the temperature rises. We’d like to focus on NTC thermistor.

I. R&D for NTC thermistor

Common NTC thermistor is made up of 2~4 transition metal oxides like Mn-Co-Ni-Fe-Cu, with ceramic sintering process. The characteristics of the thermistor is closely related to the ratio of the metal oxides, sintering conditions, and annealing conditions. One of the most important characteristics of NTC material is that resistivity ρ and B value remain the same in a quite wide range, which guarantees the consistency of products. However, when we select suitable material, NTC material is affected by material stability, sintering, consistency, thermal expansivity of the material and auxiliary material, and the cost. In order to improve the stability and working temperature of NTC thermistor, add chromium hemitrioxide, zirconium oxide, aluminium oxide or SiC into transition metal oxide to control the resistivity ρ and B value.

To be continued…

We provide various NTC thermistors with or without lugs.

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Operation points for NTC thermistor

NTC thermistor is a sensor, which has been widely used in the applications of temperature measure and control. NTC thermistor is small in size, with  fast response speed. However, users need to pay attention to the following points when using NTC thermistor.

1. NTC thermistor can withstand thermal shock of 200℃,but in order not to make thermal diode aging, the rapid changes should be prevented as far as possible for the packaging material is glass.

2. When the current is going through the thermistor, self-heating and temperature difference will be caused, which we need to consider before using.

3. Due to defective insulation and electrostatic induction, false wiring can cause that the current flowing through the thermistor is too large to damage the thermistor. Therefore, ensure there is no overcurrent through the thermistor in wiring mode.

4. For the system with high precision requirement or without thermistor resistance aging, we should use a high reliability thermal diode after high temperature testing. The circular thermistor that is often used for temperature compensation in a circuit, cannot be used in the system with variable characteristics.

5. In order to prevent heat leakage and temperature errors, we need to use the maintenance pipes, metal pipes or nonmetal pipes.

6. When there are water droplets, dust or ionic compounds surrounding the thermistor, it can lead to decrease of the resistance or measurement error, so the thermistor should be moisture-proof and insulation disposal so as to maintain itself drying.

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Mini USB color camera

ATMC102U is a kind of mini USB color camera, which has been widely used for medical care, microscope, video conference, video phone, multimedia computer toys, industrial pipe and bottom inspection, CCTV safety supervision and other applications.

There are two parts in this camera: a camera head and an USB video converter.The former has analog video / audio output signal and it is easy for the latter to connect to the computer, which can convert analog signals into digital signals.Between the two parts, there are 4 metal wires.The camera head has all of circuits, which can generate standard NTSC or PAL video / audio signals.The image sensor has a built-in color filter array, used to generate color signals.

Features

Small installation hole: 2.2mm

Compact size: 11×11×7 (mm)

Plug and play: no need to drive

High sensitivity: 0.6 lux/F1.2

Progressive scanning

High signal to noise ratio: > 50dB

Weak current: < 100mA@5V camera head 2

High resolution: 640 * 480

Analog video / audio output

Through the USB port output

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Laser power supply

Laser power supply is designed to driver high current laser diodes. The output current 0-45A can be set by the analog voltage 0-2.5V. The output voltage 0-3.5V or 0-5V can also be set. In addition, our company has a professional design team and production workshop, so we can customize products for meeting customers’ general and special requirements. I will introduce one kind of laser power supply.

Laser power supply 20A5V

High efficiency: ≥ 76%

Maximum output current: 20A

Output voltage range: 0V ~ 5V

Input voltage range: 88VAC ~264VAC

High speed digital modulation: 5 KHz

The output voltage and current limit can be set

Digital valley current can be set

Low temperature: 35°C

Over temperature protection

Working temperature: −20°C ~ 50°C

Compact size

Low cost

100% Lead (Pb)-free and RoHS compliant

If you are interested in our products, please feel free to contact us.

Our web site is http://www.analogtechnologies.com

Laser diode

Laser diode is mainly made up of semiconductor materials, thus it is also called semiconductor laser, with features such as high conversion efficiency, wide band range, long service life, direct modulation capability, compact size, light weight and low cost, etc.

Like most of lasers, laser diode has the same working principle, i.e. stimulated emission. The difference is that the electrons of the laser diode are distributed in different energy states of different energy bands, while the particles of other lasers are distributed in different energy states of active media. Therefore, there is a difference in particle numbers inversion.

Laser diode current

There are two critical diode currents: threshold current and transparency current. The former stands for the forward current when reaching the threshold gain and the latter refers to the injection current when the stimulated radiation is the same as absorbing  below the threshold value. At this time, the material absorbs no net photon, which can be seen as transparent. When the current is below the threshold current, the output of the diode is spontaneous radiation, with low power, like LED. When the current is more than threshold current, and cavity gain reaches threshold gain, laser oscillation forms.

In order to properly drive the laser diode, a laser driver is needed. Nowadays, compact size laser driver is more and more popular among electronic engineers

You may visit this page for more details of laser controller:

http://www.analogtechnologies.com/laserdriver.html

he working principle of DC-DC step down converter circuit

Switching power supply can be divided into isolation and non-isolation circuit. In this paper, we will focus on the non-isolation circuit. According to different circuit forms, it can be divided into buck circuit, boost circuit, buck-boost circuit, cuk circuit, sepic circuit and zeta circuit. Here, we mainly analyze the working principle of DC-DC step down converter circuit. As shown in figure 1, power MOSFET is an adjusting switch element and its turn-on and turn-off are determined by the control circuit. L and C are filter elements. When switching off, the diode VD can keep the output current continuous so that it is known as fly-wheel diode. When the output signal of control circuit switch on VT, the current in filter inductor L will increase gradually and the capacitor C will start to charge. Ignoring conduction drop of MOSFET, its source voltage should be Uin.

Fig. 1. The main circuit of buck DC-DC converter

According to design of TL494 (single ended buck DC-DC converter) and using continuous current mode, when the switching power supply works on CCM, the turn-on time is DT and Ii uplift amount is [(Uin-Uo) *DT]/L in a period; the turn-off time is (1-D)T and Ii uplift amount is [(Uin-Uo) *DT]/L. In the steady state, the two working principles from the top surface of the non-isolated circuit can make ILequal at the end and begining of each cycle. So the following expression can be obtained.

Sothe relationship of duty ratio D, Uin and Uo is as follows:

Fig. 2 is the main waveform of CMM buck type switching power supply.In every period, the charge transferred by ILis the same with the charge got by Io at the same time.

Fig.2. TheCMM waveform of continuous current mode

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The advantages and disadvantages of TEC modules (II)

We mentioned that do not power the TEC modules for a long time when there is no heat sink.

Here is the right installation method:

A. Install a heat sink in one side of TEC module, while the other side installs a thermal load. The installation surface flatness is less than 0.03mm. Remove any burrs or pollutant.

B. Make sure a good contact between TEC module and Thermal load, as well as TEC module and heat sink. Thermal conductive pad needs to be put in the contact surface.

C. Fix the TEC module with proper stress so as not to damage the TEC.

Operation conditions:

1. The voltage of DC power supply doesn’t exceed default voltage of the TEC modules. The ripple coefficient is less than 10%.

2. The current cannot exceed default current.

3. When the TEC is working, do not reverse the voltage instantaneously. Reverse the voltage after    5 mins.

4. The ambient humidity cannot exceed 80%.

Visit us for more details about the TEC modules and its controller.

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The advantages and disadvantages of TEC modules (I)

TEC modules (thermal electric cooler), also called Peltier modules, can cool down or heat up the object when changing the current direction. The current is DC current. There are some advantages and disadvantages of TEC module.

Advantages:

A. No cryogen needed. TEC modules can work constantly for hours. It contains no pollution or rotating components, which results no noise and vibration, long life span and easy installation.

B. Very short heating-up and cooling time due to small thermal lag in TEC modules. The max. temperature difference will be achieved within one min, under the condition of good hear dissipation in hot side and no load in cold side.

C. Thermal electric cooler is a kind of current-to -energy device. By controlling the current, high precision temperature control can be achieved. Plus temperature measurement and control, it is easy to make a automatic control system with the function of remote control, program control and computer control.

Disadvantages:

A. Single TEC modules has small power. Combine them to thermopile and then cascade or parallel these thermopiles to be a cooling system with high power, from 1mW to10KW.

B. The hot side temperature should not exceed 60°C, or it may be damaged. Do not power the TEC modules for a long time when there is no hear sink. Make sure there is enough heat dissipation devices for TEC modules.
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