Master the Basics: Diode characteristics

Diode Characteristics: How to Choose and Measure the Right Diode

When selecting a diode for your circuit, there are three primary characteristics to consider:

1. Forward Voltage (VF) – The minimum voltage required to “turn on” the diode and allow forward current to flow.

2. Breakdown Voltage (VBR) – The maximum reverse voltage the diode can withstand before it starts conducting in reverse.

3. Maximum Forward Current (IF) – The most continuous forward current the diode can handle without overheating.

Let’s explore each of these characteristics using a popular general-purpose diode: the 1N4148 Small Signal Diode.

Step 1: Finding the Diode Datasheet

Search for the part number “1N4148 datasheet” in your preferred search engine. Look for datasheets from reliable manufacturers like Vishay. The datasheet will contain essential ratings and performance specs.

Step 2: Understanding Key Ratings

From the Absolute Maximum Ratings table:

• Maximum Forward Continuous Current (IF): 300 mA – This is the current the diode can safely carry in the forward direction continuously. Exceeding it causes heat buildup.

• Peak Forward Surge Current: 2 A for 1 microsecond – This is the short-term current the diode can handle for brief spikes. Think of it like briefly passing your hand over a hot stove—it won’t burn immediately, but prolonged contact will.

Step 3: Electrical Characteristics

From the Electrical Characteristics table:

• Forward Voltage (VF): Max 1V – The diode becomes forward-biased and starts conducting current once this voltage is reached.

• Breakdown Voltage (VBR): Min 100V – The diode will block reverse current up to this voltage. Beyond it, the diode fails and allows reverse current.

In practice, the actual forward voltage is usually lower than the datasheet maximum. For the 1N4148, it typically starts conducting at around 0.6V.

Step 4: Measuring Forward Voltage with a DMM

You can test a diode using the diode test mode on your digital multimeter (DMM):

• Turn your DMM to the diode symbol.

• Place the black probe on the cathode (the side with the stripe) and the red probe on the anode.

• Your DMM will display the forward voltage—often around 0.6 to 0.7V for a standard silicon diode.

Key Takeaways

• Forward Voltage tells you when the diode will start conducting.

• Breakdown Voltage indicates how much reverse voltage the diode can block.

• Maximum Forward Current sets the safe operating limit.

These values vary slightly between components due to manufacturing differences, so always check the datasheet and test with your multimeter for precision. Choosing the right diode with the right specs ensures safe, efficient operation in your circuit.