File: /var/www/html/simulink/circuit/e-555int.html
<meta name="viewport" content="width=740">
<title>555 Internals</title>
<link rel="SHORTCUT ICON" href="favicon.ico">
<body>
<hr>
<table><tr><td>
<iframe width=740 height=600 src="circuitjs.html?startCircuit=555int.txt"></iframe>
</td><td width="20"> </td><td valign="top">
</td>
</tr></table>
<p>
This shows the (simplified) internals of a
<a href="http://en.wikipedia.org/wiki/555_timer_IC">555 timer chip</a>. As in
the <a href="e-555square.html">last example</a>, it is doing a <a href="http://en.wikipedia.org/wiki/Square_wave">square wave</a>.
<p>
A voltage divider sets the inputs of the two op-amps (used as comparators).
The upper op-amp compares the trigger input to 1/3 the supply voltage. The
lower op-amp compares the threshold input to 2/3 the supply voltage.
<p>
A timing interval starts when the trigger input goes low enough to trigger
the upper op-amp. That sets the
<a href="e-nandff.html">flip-flop</a>, causing the output
to go high. The 555 waits for the threshold input to trigger the lower
op-amp. As the capacitor charges, the threshold
input slowly rises until it reaches the required level. Then, the op-amp
resets the flip-flop, bringing the output low. The flip-flop's inverted
output also provides current to the base of the transistor on the bottom,
which discharges the capacitor through the discharge input.
<p>
When the capacitor is discharged enough so that the upper op-amp is
triggered again, a new timing interval begins.
<p>
Next: <a href="e-555saw.html">555 Sawtooth Oscillator</a><p>
Previous: <a href="e-555square.html">555 Square Wave Generator</a><p>
<a href="e-index.html#555int">Index</a><p>
<a href="index.html">Simulator Home</a>
<hr>
<script type="text/javascript"><!--
google_ad_client = "pub-1974179407250396";
/* 728x90, created 7/9/08 */
google_ad_slot = "3265434789";
google_ad_width = 728;
google_ad_height = 90;
//-->
</script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
<hr>
<a href="http://www.falstad.com/mathphysics.html"><img src="/mathphysics_small.gif"></a>
<a href="http://www.falstad.com/index.html"><img src="/me_small.gif"></a>
<br><i>java@</i><i>falstad.com</i>
<br>Generated Wed Dec 7 2016
</body>