Diodes

A diode acts as a check valve for current, allowing it to pass in only one direction from it's anode to cathode.   The silver band on a diode points to the cathode side.   Diodes have capacitance which can allow high frequency AC to pass through.   Diodes only block AC up to a certain frequency.   A 1N4148 diode performs better than the 1N400x serise in high frequency applications.  

1N4001 – 1N4007 series diodes are used in reverse polarity circuit protection.  

Schottky diodes are unipolar.   They are typically used when the circuit switching is faster than 10 nanoseconds (they also have a very low forward voltage).   Schotty diodes are good for low voltage rectifier applications.  

A transient voltage supressor (TVS) is a clamping device used to protect electronics from voltage spikes.  

Zener diodes (1N5818) are unusual in that they conduct reverse current at a particular reverse voltage threshold.   Zener diodes are typically used to maintain a constant voltage by providing them with a constant current (via a series resistor).   In a voltage regulation circuit, choose a breakdown voltage VZ that equals the load voltage, and a series resistor that will limit the current through the diode, and drop the excess voltage when the diode is conducting.  

A rectifier is composed of one or more diodes that convert alternating current to direct current.   Half-wave rectifier circuits are less efficient than a full-wave rectifier circuit.  

Thrystor diodes have three terminals, a gate, anode, and cathode.   The gate controls the current that flows between the anode and cathode.   Multiple types are available, including SCRs and TRIACs.  

Silicon Controlled Rectifiers (SCR) is a type of thrystor diode is used in high power applications.  

TRIACs are used as bidirectional switches that allow current to pass in both directions when the gate is triggered.  

Diode Applications

Reverse polarity protection using a diode is best achieved with a Schottky diode in series with the power supply connection because it has a lower voltage drop.   Look at it's forward voltage specification when choosing one.   Note that they do have a small amount of reverse current leakage.   (BAT54 circuit example).   For a 12 VDC power supply with 500 mA of current that might see up to 14.7 V under charging conditions, a Schottky diode rated at 15.0 V.   A more efficient reverse polarity protection circuit uses a PMOS (P-Channel MOSFET) rather than a Schotty diode.  

A full-bridge rectifier could be used for reverse polarity protection, but it would waste too much power.  

When you have a high energy DC switching load such as a solenoid, put a 1N4001 or 1N4004 snubber / flyback diode as close as possible across the connection to that load.  

 

Tutorial Links

Flyback Diode

Sparkfun diode tutorial

Selecting MOSFET for Reverse Polarity Protection

Applications of Diodes

Zener Diodes

Different Types of Diodes and How They Work (Jameco Electronics)

 

Under Development

 

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The information presented on this website is for the author's use only.   Use of this information by anyone other than the author is offered as guidelines and non-professional advice only.   No liability is assumed by the author or this web site.  

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