Diode equation

Hi there,

I plotted the diode equation into MathCAD and got the graph attached to this thread. How should the equation look like if I want to calculate the reverse breakdown current for e.a. a 1N4003?

I'm not sure why you think there is an equation. The reverse bias increases until the junction breaks down. The current rapidly increases causing a temperature rise in the device and eventual destruction. I don't think they come back from breakdown very often. I can tell you that a 1N4003 has a higher breakdown voltage than a 1N4001

It's called a VI curve graph "diode characteristic curves" which basically is ploted on a cartesian plane. You measure the voltage applied to the diode and the current output then plot each change in incremental steps. This is done by varying a pot from high to low and observing the meters. So you make a table and do this until the applied voltage doesn't increase, but the current increases rapidly "Junction barrier potential, si 0.7 volts, and germanium 0.3V" This point is called the knee region (when the diode is fully conducting). This will be in the first quadrant. If you reverse bias the diode and do the same thing you can find the break down voltage plot when the voltage remains constant, but a huge current starts to flow. This is called the diode breakdown or "Peak inverse voltage (PIV)", and if there isn't a current limiting device(resistor) it will burn up the diode. This break down curve is plotted in quadrant 3.

Usually diodes recover perfectly from a breakdown condition, but if a proper resistor wasn't used it would cause diode burn out... bbq

This information varies from diode to diode and is already calculated in the specific data sheet for the device.

If there is an equation for this.. then please share

**broken link removed** has reverse breakdown equations, but I have never seen them before, and have no idea if they are valid, or how you would obtain the parameters in the equations. In other words, you're probably on your own.

Ron H said:

**broken link removed** has reverse breakdown equations, but I have never seen them before, and have no idea if they are valid, or how you would obtain the parameters in the equations. In other words, you're probably on your own.

Click to expand...

I've never had occasion to use them either since almost all the circcuits I've ever built, besides all the ones that I haven't built, pretty much tend to stay away from the breakdown region. It does give some insight into how SPICE simulators work which is always a handy thing. Thanks Ron.