e_diode.htm.mht

5V到30V升压电源设计

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<br>
<img src=3D"index_files/dbrige.gif" alt=3D"" align=3D"left" height=3D"298" w=
idth=3D"283"><font size=3D"2">Rectification
diodes are used to make DC from AC. It is possible to do only 'half
wave rectification' using 1 diode. When 4 diodes are combined, 'full
wave rectification' occurrs.</font><br>
<font size=3D"2">Devices that combine 4 diodes in one package are called dio=
de bridges. They are used for full-wave rectification.</font><br>
<br clear=3D"left">
<br>
<br>
<br>
<br>
<img src=3D"index_files/rect1.jpg" alt=3D"" align=3D"left" height=3D"218" hs=
pace=3D"10" vspace=3D"10" width=3D"308"><br>
<font size=3D"2">The photograph on the left shows two examples of diode brid=
ges.</font><br>
<br>
<font size=3D"2">The cylindrical device on the right in the photograph
has a current limit of 1A. Physically, it is 7 mm high, and 10 mm in
diameter.</font><br>
<font size=3D"2">The flat device on the left has a current limit of 4A. It i=
s has a thickness of 6 mm, is 16 mm in height, and 19 mm in width.</font><br=
>
<br>
<br clear=3D"left">
<img src=3D"index_files/rect2.jpg" alt=3D"" align=3D"right" height=3D"217" h=
space=3D"10" vspace=3D"10" width=3D"308"><br>
<br>
<font size=3D"2">The photograph on the right shows a large, high-power diode=
 bridge.</font><br>
<font size=3D"2">It has a current capacity of 15A. The peak reverse-bias vol=
tage is 400V.</font><br>
<font size=3D"2">Diode bridges with large current capacities like this
one, require a heat sink. Typically, they are screwed to a piece of
metal, or the chasis of device in which they are used. The heat sink
allows the device to radia
te excess heat.</font><br>
<font size=3D"2">As for size, this one is 26 mm wide on each side, and the h=
eight of the module part is 10 mm.</font><br>
<br clear=3D"right">
<hr><br>
<a name=3D"led"></a><img src=3D"index_files/bol_s_gy.gif" alt=3D"" align=3D"=
bottom" height=3D"14" width=3D"14"> <font size=3D"4">Light Emitting Diode ( =
LED )</font><br>
<img src=3D"index_files/led.jpg" alt=3D"" align=3D"right" height=3D"190" hsp=
ace=3D"10" vspace=3D"10" width=3D"366"><br>
<font size=3D"2">Light emitting diodes must be choosen according to how they=
 will be used, because there are various kinds.</font><br>
<font size=3D"2">The diodes are available in several colors. The most common=
 colors are red and green, but there are even blue ones.</font><br>
<br>
<font size=3D"2">The device on the far right in the photograph combines a
red LED and green LED in one package. The component lead in the middle
is common to both LEDs. As for the remaing two leads, one side is for
the green, the other for the red LED. When both are turned on
simultaneously, it becomes orange.</font><br>
<br>
<font size=3D"2">When an LED is new out of the package, the polarity of
the device can be determined by looking at the leads. The longer lead
is the Anode side, and the short one is the Cathode side.</font><br>
<br>
<font size=3D"2">The polarity of an LED can also be determined using a resis=
tance meter, or even a 1.5 V battery.</font><br>
<br>
<font size=3D"2">When using a test meter to determine polarity, set the
meter to a low resistance measurement range. Connect the probes of the
meter to the LED. If the polarity is correct, the LED will glow. If the
LED does not glow, switch the meter probes to the opposite leads on the
LED. In either case, the side of the diode which is connected to the
black meter probe when the LED glows, is the Anode side. Positive
voltage flows out of the black probe when the meter is set to measure
resistance.</font><br>
<br>
<br clear=3D"right">
<img src=3D"index_files/ledloge.gif" alt=3D"" align=3D"left" height=3D"142" =
hspace=3D"10" vspace=3D"10" width=3D"206"><br>
<br>
<font size=3D"2">It is possible to use an LED to obtain a fixed voltage.</fo=
nt><br>
<font size=3D"2">The voltage drop (forward voltage, or V<sub>F</sub>) of an =
LED is comparatively stable at just about 2V.</font><br>
<br>
<font size=3D"2">I explain a circuit in which the voltage was stabilized wit=
h an LED in "</font><a href=3D"http://www.interq.or.jp/japan/se-inoue/e_acry=
la6.htm"><font size=3D"2">Thermometer of bending apparatus-2</font></a><font=
 size=3D"2">".</font><br>
<br clear=3D"left">
<hr><br>
<a name=3D"diode4"></a><img src=3D"index_files/bol_s_gy.gif" alt=3D"" align=
=3D"bottom" height=3D"14" width=3D"14"><font size=3D"4"><b> </b>Shottky barr=
ier diode</font><br>
<br>
<img src=3D"index_files/shottky_diode.jpg" alt=3D"" align=3D"left" height=3D=
"150" hspace=3D"10" vspace=3D"10" width=3D"152"><font size=3D"2">Diodes
are used to rectify alternating current into direct current. However,
rectification will not occur when the frequency of the alternating
current is too high. This is due to what is known as the "reverse
recovery characteristic."</font><br>
<font size=3D"2">The reverse recovery characteristic can be explained as fol=
lows:</font><br>
<font size=3D"2">IF the opposite voltage is suddenly applied to a
forward-biased diode, current will continue to flow in the forward
direction for a brief moment. This time until the current stops flowing
is called the Reverse Recovery Time. The current is considered to be
stopped when it falls to about 10% of the value of the peak reverse
current.</font><br>
<font size=3D"2">The Shottky barrier diode has a short reverse recovery
time, which makes it ideally suited to use in high frequency
rectification.</font><br>
<br>
<br clear=3D"left">
<br>
<br>
<font size=3D"2">The shottky barrier diode has the following characteristics=
.</font><br><ul>
<img src=3D"index_files/bol_s_gr.gif" alt=3D"" align=3D"bottom" height=3D"11=
" width=3D"11"><font size=3D"2"> The voltage drop in the forward direction i=
s low.</font><br>
<img src=3D"index_files/bol_s_gr.gif" alt=3D"" align=3D"bottom" height=3D"11=
" width=3D"11"><font size=3D"2"> The reverse recovery time is short.</font><=
br>
</ul><font size=3D"2">However, it has the following disadvantages.</font><br=
><ul>
<img src=3D"index_files/bol_s_rd.gif" alt=3D"" align=3D"bottom" height=3D"11=
" width=3D"11"><font size=3D"2"> The diode can have relatively high leakage =
current.</font><br>
<img src=3D"index_files/bol_s_rd.gif" alt=3D"" align=3D"bottom" height=3D"11=
" width=3D"11"><font size=3D"2"> The surge resistance is low.</font><br>
</ul>
<font size=3D"2">Because the reverse recovery time is short, this diode is o=
ften used for the switching regulator in a high frequency circuit.</font><br=
>
</td>
</tr>
</tbody></table><br></div><p></p></body></html>


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