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<?xml-stylesheet type="text/xsl" href="https://community.arm.com/utility/feedstylesheets/rss.xsl" media="screen"?><rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:slash="http://purl.org/rss/1.0/modules/slash/" xmlns:wfw="http://wellformedweb.org/CommentAPI/"><channel><title>Microcontroller software shutdown with transistor 2N4401</title><link>https://community.arm.com/developer/tools-software/tools/f/keil-forum/35868/microcontroller-software-shutdown-with-transistor-2n4401</link><description> 
I am trying to understand why connecting, say, an Arduino digital
pin 4 to a 2N4401 pin 2 as well as 5V PSU to 2N4401 pin 1 and Arduino
VCC to 2N4401 pin 3, won&amp;#39;t keep power. 

 
When shorting pin 1 and pin 3 on the 2N4401 the MCU is powered on
and</description><dc:language>en-US</dc:language><generator>Telligent Community 10</generator><item><title>RE: Microcontroller software shutdown with transistor 2N4401</title><link>https://community.arm.com/thread/120919?ContentTypeID=1</link><pubDate>Tue, 27 Dec 2016 09:15:27 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:8b4914df-5072-4e94-9fa0-0d37698000df</guid><dc:creator>Andy Neil</dc:creator><description>&lt;p&gt;&lt;p&gt;
Which, of course, has nothing to do with Keil!&lt;/p&gt;

&lt;p&gt;
Perhaps this might help:&lt;/p&gt;

&lt;p&gt;
&lt;a href="http://electronicsclub.info/transistors.htm"&gt;electronicsclub.info/transistors.htm&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;
&lt;a href="http://electronicsclub.info/transistorcircuits.htm"&gt;electronicsclub.info/transistorcircuits.htm&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;
Or any of the many other basic electronics tutorial websites &amp;amp;
books available...&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: Microcontroller software shutdown with transistor 2N4401</title><link>https://community.arm.com/thread/108991?ContentTypeID=1</link><pubDate>Tue, 27 Dec 2016 08:43:36 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:a531145a-dd35-4f2d-95a1-55027f8b6da3</guid><dc:creator>edPer Westermark</dc:creator><description>&lt;p&gt;&lt;p&gt;
I wasn&amp;#39;t talking about the processor - I was talking about the pin
numbers for the transistor:&lt;br /&gt;
&amp;quot;&lt;b&gt;to a 2N4401 pin 2&lt;/b&gt; as well as 5V PSU &lt;b&gt;to 2N4401 pin 1&lt;/b&gt;
and Arduino VCC &lt;b&gt;to 2N4401 pin 3&lt;/b&gt;&amp;quot;&lt;/p&gt;

&lt;p&gt;
Way easier to talk about base, emitter and collector when talking
about how a NPN/PNP transistor is connected.&lt;/p&gt;

&lt;p&gt;
What it has to do with Keil? The OP suspects he is doing something
wrong with the I/O pin of the processor while not realizing he is
missing how a NPN transistor behaves.&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: Microcontroller software shutdown with transistor 2N4401</title><link>https://community.arm.com/thread/93858?ContentTypeID=1</link><pubDate>Tue, 27 Dec 2016 08:09:45 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:f0285c80-4d19-4837-9b57-1bfdaec026bb</guid><dc:creator>Andy Neil</dc:creator><description>&lt;p&gt;&lt;p&gt;
But the OP is talking about &lt;b&gt;Arduino&lt;/b&gt; - where, AIUI, these
&lt;i&gt;are&lt;/i&gt; specifically defined.&lt;/p&gt;

&lt;p&gt;
But the question then becomes: &lt;b&gt;What on earth does this have to
do with &lt;i&gt;Keil&lt;/i&gt;??&lt;/b&gt;&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item><item><title>RE: Microcontroller software shutdown with transistor 2N4401</title><link>https://community.arm.com/thread/69740?ContentTypeID=1</link><pubDate>Tue, 27 Dec 2016 02:38:22 GMT</pubDate><guid isPermaLink="false">dd9e70c8-6d3c-4c71-b136-2456382a7b5c:0e4f4ccd-329c-42bf-9b3d-2bdad6f667ed</guid><dc:creator>edPer Westermark</dc:creator><description>&lt;p&gt;&lt;p&gt;
Pin 1, 2, 3 aren&amp;#39;t really good names - they depend on type of
package. That&amp;#39;s why school books talks about base, collector and
emitter. And why schematics uses a transistor symbol that graphically
displays base, collector and emitter.&lt;/p&gt;

&lt;p&gt;
A FET is best to use since they are voltage-controlled while a
bipolar transistor is current-driven. So the gain of the transistor
decides how much current you need to send in on the base. Then you
need some extra current just to make sure it really is fully open -
i.e. saturated. A bipolar transistor isn&amp;#39;t linear all the way to max.
To send in that base current, you need to have enough voltage
potential on the pin. Your selected transistor is NPN - the data
sheet notes that the minimum base-emitter saturation voltage is 0.75V
and max is 0.95V. Suddenly you should start to see an issue here -
how can the processor GPIO pin output be held almost a volt higher
than the supply voltage you feed to the processor?.&lt;/p&gt;

&lt;p&gt;
An NPN transistor is easier to work with as a sink, i.e. on the
ground side, since it&amp;#39;s easier to control the base voltage relative
to the emitter if the emitter is grounded. If the emitter voltage can
float up/down, then you need to have the base voltage also float
up/down. But you still wouldn&amp;#39;t want that NPN transistor between
processor GND and real GND because you would get a voltage drop you
wouldn&amp;#39;t like. You really (!) want to keep all ground points as close
to 0V as possible, i.e. to have virtually zero resistance.&lt;/p&gt;

&lt;p&gt;
Best for you: go get a transistor that is well suited for the
task.&lt;/p&gt;
&lt;/p&gt;&lt;div style="clear:both;"&gt;&lt;/div&gt;</description></item></channel></rss>