The base-emitter junction of a BJT has a very predictable transfer function that is dependent on temperature. Both temperature and voltage affect the diode’s reverse current, so I used a steady 5VDC power source while taking the DVM readings. And I found that the reverse leakage current is pretty small – around 3 nano amperes (nA) only. I’ve measured the reverse current of a 1N4148 diode as well using the setup shown below. You should also note that the reverse current of a diode can even be used as a temperature sensor. it changes according to the amount of forward voltage and current going through the diode at any particular time. Further, the “Bulk Resistance” of a diode is the approximate resistance across the terminals of the diode when a forward voltage and current are applied across it. Side note: For a silicon diode, the barrier voltage for current flow to occur is above the point of 700mV, and it’s above the 300mV point for a germanium diode. Anyway, you’re free to opt for a constant current source for driving the diode – look below. The single resistor is enough here because the forward voltage drop of the diode doesn’t change much and hence the current through the resistor is reasonably constant. Below you can see the merest 1N4148 temperature sensor idea. My pick is intentional as the DO-35 package diode has a non-melty glass shell that’s appropriate for my ‘hot’ applications. I’ve been using the 1N4148 small-signal silicon diode ( ) as a temperature sensor in a few hobby electronics projects. So, if you keep the current constant and read the forward voltage, yes, you’ve got yourself a pretty simple temperature sensor diode! Sounds great, right? That’s okay, but remember that this voltage drop is influenced by the current that flowing through the diode (I F) and the temperature closely encircling the diode. You know that the typical forward voltage drop (V F) of a common silicon diode is 700mV or so. This is because the relationship is fairly linear with about 2mV less voltage drop for every degree increase of temperature (-2mV/☌). It’s worth noting again that a diode can be used as a temperature sensor, and most diode-based temperature sensors use the change in forward voltage. Since they’re true analog components, you don’t need to write lengthy codes and/or call special third-party libraries even if used them in your relatively complex microcontroller projects! Temperature Sensor Diode – Forward That’s fine, but in this article, I’ll explain how to use common bipolar junction transistors and small signal diodes as accurate temperature monitors/sensors. When it comes to everyday temperature sensing, the thermistor is the most simple and inexpensive component to get temperature data at ease.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |