Editing Reverse Protection Diodes
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Obviously there must be a way to prevent this from happening. Enter diodes... | Obviously there must be a way to prevent this from happening. Enter diodes... | ||
− | These pieces of silicon allow current to flow in one direction only. Quite simply, VCC is | + | These pieces of silicon allow current to flow in one direction only. Quite simply, VCC is allow through but GND is not. Why don't we put a diode on every VCC? Well a diode can cause a 0.7V drop (that's what they teach you in silly eng school at least) on the power line. So if you are dealing with a really low-power system, 0.7V drop can be too much. |
There are other ways to protect against reverse polarization like polarized connectors and certain voltage regulators have protection built in. But it you're designing something for mass-market where you don't know who will be connecting what, a reverse protection diode is cheap and easily designed into a board. | There are other ways to protect against reverse polarization like polarized connectors and certain voltage regulators have protection built in. But it you're designing something for mass-market where you don't know who will be connecting what, a reverse protection diode is cheap and easily designed into a board. | ||
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[[Image:PG31-PowerSupply-Schematic.jpg]] | [[Image:PG31-PowerSupply-Schematic.jpg]] | ||
− | Here you can see the diode D3 in place | + | Here you can see the diode D3 in place. |
− | These type diodes can also be used, four at a time, in an [http://en.wikipedia.org/wiki/Diode_bridge bridge rectifier] configuration. I don't have a good image (now you do), but an bridge rectifier takes an AC signal and rectifies it to a DC signal (neat trick actually). | + | These type diodes can also be used, four at a time, in an [http://en.wikipedia.org/wiki/Diode_bridge bridge rectifier] configuration. I don't have a good image (now you do), but an bridge rectifier takes an AC signal and rectifies it to a DC signal (neat trick actually). An bridge rectifier circuit will also work with a DC supply. |
− | Diodes come in all shapes and sizes. For this posting, we only care about cheap, bulky, large current diodes. These diodes can handle 1-2A each and are cheap. For some our mass designs, we prefer the surface mount diodes (MBRA140). The MBRA140 comes in an SMA package (hopelessly confused with the SMA antenna connector - who came up with this?!). Many other diodes come in axial packages perfect for bread boarding. They all work the same - there is an anode and a cathode. I was always told to remember the <b>a</b>node | + | Diodes come in all shapes and sizes. For this posting, we only care about cheap, bulky, large current diodes. These diodes can handle 1-2A each and are cheap. For some our mass designs, we prefer the surface mount diodes (MBRA140). The MBRA140 comes in an SMA package (hopelessly confused with the SMA antenna connector - who came up with this?!). Many other diodes come in axial packages perfect for bread boarding. They all work the same - there is an anode and a cathode. I was always told to remember the <b>a</b>node was the <b>a</b>rrow and current flows in the direction of the arrow. Cool huh? |
We like the MBRA140 cause it's cheap and can handle up to 1A. One amp is overkill for most applications, but that's why it's good, it'll work with most applications. If you need something less burly, Digikey/Mouser has more than plenty. Be sure to get a diode that is current rated for the max current draw of your system. If the diode is too small, it'll heat up and eventually burn out. | We like the MBRA140 cause it's cheap and can handle up to 1A. One amp is overkill for most applications, but that's why it's good, it'll work with most applications. If you need something less burly, Digikey/Mouser has more than plenty. Be sure to get a diode that is current rated for the max current draw of your system. If the diode is too small, it'll heat up and eventually burn out. | ||
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<b>Documents:</b><br> | <b>Documents:</b><br> |