Hello readers! Today we will talk about some basic electronics topic and that is paralleling diodes. When you connect two diodes in parallel hoping that the current will be shared across each diode, you might be right but in most of the cases you would be wrong! Let's say you want to share 10A current across two diodes of current handling capacity of 5A, what's gonna happen is diodes will heat up and due to their internal resistance and temperature depending characteristics, the resistance of one of the diode decreases. Now, why one of the diode? It is because the thermal characteristics of both the diodes are very less probable to be exact. So what happens is one of the diode will heat up more than the other.





As the temperature increases, resistance of that diode decreases and will try to carry much larger current and it will continue to heat up until it carries a complete 10A across it and smoke up. Then of course, the 10A current will pass thorough other diode and smoke that too. So, it may be a bad design idea to parallel diodes.











Two diodes in parallel can be forced to share equal currents with the help of resistors. If you a low value resistor is connected, for example 1 ohm or 1/2 ohm, something like that, in series with each diode, and then parallel those assemblies, the resistors help to keep the load even between the two diodes. If one diode starts to take more of the load current, the current drop on the resistor lowers the voltage for that diode, tending to push the current back down.





Another thing you can do is connect one more diode in parallel to share 1/3 of load across each diode. However, you need to add two resistors to balance the load and so it can be an economic solution in some applications to just add another diode in parallel. You can also improve the PCB layout for balancing the resistance in series of each diode. Have a look at the figure below! The resistance in series with each diode must be kept equal otherwise the circuit will de-stabilized and again of the diode will try to carry more current.









Other way to reduce these effects will be to use a common heat-sink for both the diodes. This will no doubt reduce the effects due to the fact that the heat sink will try to maintain temperature of each diode. But it is still not recommended to use this and this is also not a very economical solution, if you can employ a common wide heat sink then why not an extra diode.





As long as both the diodes are thermally coupled, you might be good to go in theory but practically, one diode will always get hotter than the other. SIC semiconductor material diode is however guaranteed to equalize current across them but they are too expensive!

Enter your email address: Delivered by FeedBurner





So, all these discussions leads us to a couple of viable solutions and that is adding an extra diode or for expensive diodes, stabilize the network with resistors or PCB traces.





More suggestions:





1. Try using a single big diode with more current handling capacity than using two diodes in parallel.





2. This is the obvious one, choose the diodes with less forward voltage drop for less heating effect.





If you liked the article, please share, follow and comment!

Thanks for reading!