Electronics > Beginners
Diodes in parallel.
Zero999:
--- Quote from: ArthurDent on July 18, 2018, 01:07:12 pm ---As others have pointed out, using bigger/more diodes can create problems with reverse leakage/unequal current sharing. Here is a good simple video that covers what you are trying to accomplish. A single cheap mosfet can work in most applications. Because mosfets are basically low value resistors when turned on they would be much easier to parallel without any added equalization circuitry if you needed really large currents.
--- End quote ---
I can't watch the video at the moment.
MOSFETs are good for switching between several power supplies or reverse polarity protection, but they don't behave like diodes, without an external controller IC. If two slightly different voltage power supplies are connected together, via P-channel MOSFETs, then they'll just get shorted together, when the MOSFETs turn on.
In the prototype I worked on, lots of 1N5822 diodes were connected in parallel, which worked out much cheaper, than a more beefy diode and the package was more convenient for a quick lash-up, than an SMT package.
wraper:
--- Quote from: Hero999 on July 18, 2018, 01:18:08 pm ---In the prototype I worked on, lots of 1N5822 diodes were connected in parallel, which worked out much cheaper, than a more beefy diode and the package was more convenient for a quick lash-up, than an SMT package.
--- End quote ---
Did you dare to use thermal imager?
Zero999:
--- Quote from: wraper on July 18, 2018, 02:21:43 pm ---
--- Quote from: Hero999 on July 18, 2018, 01:18:08 pm ---In the prototype I worked on, lots of 1N5822 diodes were connected in parallel, which worked out much cheaper, than a more beefy diode and the package was more convenient for a quick lash-up, than an SMT package.
--- End quote ---
Did you dare to use thermal imager?
--- End quote ---
No, there was no need to because none of the devices came anywhere near to overheating. Using multiple, smaller devices also spread the heat, over a larger area, which removed the need for a heat-sink. The voltage drop was significantly lower, with all the devices in parallel, than the equivalent big rectifier and was sufficient for the application, which only needed 10A continuously, 15A peak and 8×3A diodes gave ample headroom.
It simply isn't true that one diode hogs all of the current. It's true that current sharing is not perfect, but it's not all or nothing, like you're implying. This isn't the same as connecting multiple discharge tubes in parallel, which would indeed result in one device firing, leaving the others unused.
chemelec:
When using diodes in Parallel it is recommended to put a Separate Series Resistor to each diode.
Resistor Values depend on actual current, but somewhat Low Value resistors.
These Resistors will help to even out differences between the Diodes.
Zero999:
--- Quote from: chemelec on July 18, 2018, 02:57:08 pm ---When using diodes in Parallel it is recommended to put a Separate Series Resistor to each diode.
Resistor Values depend on actual current, but somewhat Low Value resistors.
These Resistors will help to even out differences between the Diodes.
--- End quote ---
That's true, resistors will help to improve the current sharing, other than increased component count, the downsides are increased voltage loss and power dissipation, hence why I didn't even consider using them.
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