The relationship among PCB copper thickness, trace width and current

In PCB design, OZ is normally used as the unit of copper thickness. 1OZ copper thickness is defined as the copper foil within 1 square inches area weighs 1 ounces, the corresponding physical thickness is 35um.

Below is the ampacity table of the copper foil with different thickness and different width

copper thickness 70um       copper thickness 50um        copper thickness 35um
copper sheet t=10             copper sheet t=10             copper sheet  t=10
current A  width mm       current A  width mm          current A   width mm

6.00    2.50                       5.10    2.50              2.50    4.50
5.10    2.oo                       4.30    2.00              4.00    2.00
4.20    1.50                       3.50    1.50              3.20    1.50
3.60    1.20                       3.00    1.20              2.70    1.20
3.20    1.00                       2.60    1.00              2.30    1.00
2.80    0.80                       2.40    0.80              2.00    0.80
2.30    0.60                       1.90    0.60              1.60    0.60
2.00    0.50                       1.70    0.50              1.35    0.50
1.70    0.40                       1.35    0.40              1.10    0.40
1.30    0.30                       1.10    0.30              0.80    0.30
0.90    0.20                       0.70    0.20              0.55    0.20
0.70    0.15                       0.50    0.15              0.20    0.15

Note: When using copper as ampacities wire through the current, the carrying capacity of copper foil width should be considered with the reference table in the value of the amount of 50%. Because the thickness of copper foil laminate is limited, the carrying capacity of copper foil should be considered when a large current through the copper strip is needed.

Take typical 0.03 mm thickness as example, if take copper foil as the strip conductor with width as W(mm), length as L(mm), its resistance should be 0.0005*L/W ohm. The installation capacity of copper foil is related with the type, quantity and cooling conditions of the component on a printed circuit board. In consideration of safety, generally take the 0.15*W (A) empirical formula to calculate the ampacity of copper foil.

The calculation method for the PCB copper foil width and the size of the electric flux:

When the general thickness of copper foil for PCB board is 35um, the line width is 1mm, then the area of the transverse section of the line is 0.035 square mm. Usually take current density 30A/ square mm, so there is 1A current for per mm line width.

There is calculation formula in IPC275-A standard, related with the rise of temperature, the thickness of copper foil, A

I = 0.0150(DT 0.5453)(A 0.7349) for IPC-D-275 Internal Traces
I = 0.0647(DT 0.4281)(A 0.6732) for IPC-D-275 External Traces copper sheet

DIY Automatic temperature controller for electric fan

This is a Automatic temperature controller for electric fan, which automatically adjusts the speed and circuit of electric fan according to the temperature change, which it also suit to the control of other electrical equipments.

  1. Circuit working principle

The IC, a 555 Timing Circuit in below image, constitutes a multivibrator with components like R2, R3 and C2, which can send a rectangular wave signal of adjustable duty ratio.

When the temperature changes, the resistance of the thermistor varies to change the duty cycle of the multivibrator output square wave and regulate the conduction angle of the bidirectional thyristor  VT, thereby bring to the change of the voltage at both ends of the fan electrode, and the automatic adjustment of the speed of the electric fan.

  1. Component selection

Integrated circuit (IC) uses NE 555 Timing Circuit, also OK with other model like LM555 and TLC555.

VT should be the bidirectional thyristor whose withstand Voltage should be over 400V, the rated current selection should be based on the control of the fan capacity.

Resistance R1 ~ R5 can be used as ordinary 1/8 or 1/4W carbon film resistors.

Rt, negative temperature coefficient thermistor, it is OK with Thermistor with 10KΩ room temperature.

Capacitor C1 can choose ordinary aluminum electrolytic capacitors, Capacitor C2 and C3 to be polyester capacitors.

VD for the regulated value of 9.1V voltage regulator diode

  1. Method of production and debugging

You can use both Self made printed circuit boards and universal boards when production. After the completion of the circuit installation, it is OK to adjust the temperature of the thermistor Rt by hand and observe the rotate speed of fan motor.  If with unsatisfactory temperature control effect, adjust properly the resistance of the thermistor and temperature range

PCB routing standard for PI

  1. The area of the circuit-switched ring is reduced as far as possible in order to reduce the induced noise.
  2.  Power lines and ground wires should be as thick as possible. In addition to reducing the pressure drop, it is more important to reduce the coupling noise.
  3. For spare I/O port of single chip, do not hang but connect to the ground or the power supply. The idle end of other IC is also the case without changing the logic of the system;
  4. Using power supply monitor and watchdog circuit for single chip microcomputer, such as: IMP809,IMP706,IMP813,X25043,X25045 and so on, then will greatly improve the anti-interference performance of the whole circuit .
  5. IC device should be directly to welded on the circuit board as far as possible, to avoid the usage of IC socket.
  6. The transmission signal is as close as possible to the signal circuit, so as to prevent the radiation of the circuit area surrounded by these lines and reducing of the magnetic susceptibility of the loop induced voltage.
  7.  Drill the vias nearby the pins of the power and ground. The lead wire between the hole and the pin should as short as possible, which will increase the inductance. At the same time, the power supply and the ground wire should be as thick as possible to reduce the impedance.
    8. Place a few ground through holes near the hole in the signal layer, so as to provide nearest circuit for the singles. Even large number of excess ground through holes can be placed on the PCB board
  8. Use buried vias
  9. Any high speed and high power devices should be placed together in order to reduce the transient overshoot of the power supply voltage
  10.  Avoid taking long Power connection, because the long power supply connection can form the loop between the signal and the circuit, and then becomes the radiation source and the easy induction circuit.

PCB design output with PowerPCB

PCB design can be output to the printer or output Gerber files. The printer can print the PCB design layer by layer, which is easy checking for designers and double checkers. Gerber files can be provided to PCB manufacturer for PCB production. The Gerber file output is very important, and decides the success or failure of the design.  The following will focus on the attention for Gerber file output.

  1. The layers that needed are: Routing layer (including top, bottom and middle routing layers), Power layer (containing VCC layer and GND layer), silkscreen layer (top and bottom silkscreen layers), solder mask layers (top and bottom), as well as drill file (NC drill).
  2. If set power layer as “Split/Mixed”, then choose “add document” window-“Document”-“routing”, and before every Gerber file output, always use “Pour manager”- “Plane connect” to achieve copper clad for PCB design; If set power layer as “CAM Plane”, add “layer 25” when setting “layer” , and choose “Pads” and “Vias” in layer 25.
  3. Pull “Device Setup” in Setting window, and change the value of Aperture as 199.
  4. Pick “ board outline” when set “Layer” for every layer
  5. For “layer” setting for every silkscreen layer, Do not pick “Part Type”, but “top (bottom) layer” and “Outline”、 “Text”、 “Line” of silkscreen layer.
  6. For solder mask layer, choose “vias” mean no solder mask on Vias, otherwise means adding solder mask, which depends on the practical cases.
  7. When generate the drill file, use the default settings for PowerPCB, and do not make any changes.
  8. All Gerber files output, open with CAM350 for checking.26

Reasons for poor refrigeration of air conditioners

Summer comes, the home begins to use air conditioning. While many families found their air conditioners are with poor refrigeration. Below are some reasons and methods for instructions

Reason 1: insufficient Freon

It is the normal case with insufficient Freon, which happens in air conditioners with 3-4 years usage. The air conditioners are not totally without cooling but not good enough. Old air conditioning normally use Freon as refrigerants, which will volatilize with longtime usage. In addition, Freon omission caused by improper installation and machine itself will also the reasons.

Solution: Add certain refrigerant will be alright.

Reason 2: inadequate voltage of power supply

Supply voltage is not stable to reach the normal voltage, especially in peaks in energy demand. The question can not tend to the help of a Skillful maintenance master, but providing stable voltage is necessary.

Solution: providing stable power Supply Voltage

Reason 3: lack of power

There are many reasons for the lack of power, such as low-powered air conditioners service for large-area room. Though some air conditioners seems have the power matching with the room size, while the room Is relatively non-airtight (such as large open doors or windows), or there is heat sources.

Solution: make its power match with the needed refrigerating capacity; Change the condition of application environment; Add its airtightness; Reduce the heat sources in using environment.

Reason 4: High ambient temperature.

outdoor machines were installed in relatively enclosed spaces or places with high surround temperature, which will block the running of the heat from the radiator and lead to the poor refrigeration.

Solution: Change the environment of the outdoor unit (remove from hot environment or flowing surrounding environment.

Reason 5: no cleanup and maintenance for a long time

It does not mean everything will be fine after air conditioners buying. Since outdoor machines are installed outside, there will be much dirt like dust and mess absorbed on the radiator, which will bring bad heat dissipation. In addition, unhygienic room air without certain maintenance will easily lead to air-condition disease, Increase in power consumption, Shorten the service life of the air conditioner.

Solution: Regular cleanup and maintenance, keep clean outdoor machines