circuitjs1-zh
/
mosfet-beta.html

<html><head>
<meta http-equiv="content-type" content="text/html; charset=windows-1252"><style>#header + #content > #left > #rlblock_left,
#content > #right > .dose > .dosesingle,
#content > #center > .dose > .dosesingle
{display:none !important;}</style><style>img[src="http://s05.flagcounter.com/count/pTvk/bg=FFFFFF/txt=000000/border=CCCCCC/columns=6/maxflags=36/viewers=0/labels=0/"]
{display:none !important;}</style></head><body><h1>MOSFET Beta</h1>
We use a parameter called "beta" to describe the behavior of a MOSFET.  The default value is small (20m), which is appropriate for a signal MOSFET.  To simulate
a power MOSFET, use a larger value like 80.
<p>
In the saturation region, I<sub>ds</sub> = beta * (V<sub>gs</sub> - V<sub>t</sub>)<sup>2</sup>/2.
<p>
This worksheet will calculate the value of beta for a particular MOSFET, given Rds(on).
<p>

<script>


function units(x) {
	 x = x.trim();
   if (x.match(/m$/)) {
       x = x.replace(/m$/, "");
  	return .001 * x;
   }
   // don't think we need this but you never know
   if (x.match(/u$/)) {
       x = x.replace(/u$/, "");
       return 1e-6 * x;
   }

   return x;
}

function calc() {
   var rds = units(document.getElementById('rds').value);
   var vgs = units(document.getElementById('vgs').value);
   var vt = units(document.getElementById('vt').value);
   var beta = Math.abs(1/(rds*(vgs-vt)));
   document.getElementById('result').innerHTML = "beta = " + beta;
}

</script>
<form action="/action_page.php">
  R<sub>DS</sub>(on) (&#x2126;) (use typical value): <input type="text" id="rds" oninput="calc()"><br>
  V<sub>GS</sub> where measured (V): <input type="text" id="vgs" oninput="calc()"><br>
  Threshold (V) (use typical value): <input type="text" id="vt" oninput="calc()"><br>
</form>
<div id="result">

</div>

</body></html>