What is a schottky diode?

Summary

This video tutorial delves into Schottky diodes, contrasting them with standard silicon diodes. It highlights Schottky's lower forward voltage drop, resulting in less heat and higher efficiency, exemplified by a comparison between a 1N4007 silicon diode and a 1N5817 Schottky diode. The video also addresses Schottky's superior switching speeds, ideal for high-frequency applications like switch-mode power supplies. However, it cautions about their higher reverse leakage current, which can be significant in certain circuits. Lastly, it advises on selecting diodes based on peak reverse voltage for optimal performance.

Takeaways

• 🔍 Schottky diodes have a distinct circuit symbol and behave differently from regular silicon diodes.
• 💡 Diodes allow current to flow in one direction and have a forward voltage drop (Vf) which generates heat.
• 🌡️ Schottky diodes have a lower forward voltage drop than silicon diodes, leading to less heat generation.
• 📉 An example shows that a 1N5817 schottky diode generates less heat compared to a 1N4007 silicon diode under the same current.
• 🚀 Schottky diodes are more efficient for blocking reverse current flow due to their lower Vf.
• 📊 The forward voltage drop (Vf) of schottky diodes can be found from the datasheet and varies with current and temperature.
• 🏎️ Schottky diodes have fast switching speeds, making them suitable for high-frequency applications.
• 📻 A demonstration shows schottky diodes handle high frequencies better than silicon diodes in a rectification experiment.
• ⚠️ Silicon diodes have a lower reverse leakage current compared to schottky diodes, which is critical in some applications.
• 🔌 The forward voltage drop of a diode is related to its maximum voltage rating, impacting efficiency and selection for specific uses.

Q & A

What is a Schottky diode?

A Schottky diode is a type of semiconductor diode that has a lower forward voltage drop and faster switching speeds compared to regular silicon diodes. It is used for efficient blocking of reverse current flow.

How does the circuit symbol of a Schottky diode differ from that of a regular silicon diode?

The circuit symbol for a Schottky diode is similar to other diodes, but it is important not to confuse them as they behave differently.

What is the significance of the forward voltage drop (Vf) in diodes?

The forward voltage drop (Vf) across a diode is the voltage difference when current is flowing through it in the forward direction. It results in heat generation, calculated by Vf multiplied by the current.

Why are Schottky diodes more efficient than silicon diodes?

Schottky diodes have a lower forward voltage drop, which means less heat is generated for the same current, leading to higher efficiency.

What is the forward voltage drop of a 1N4007 silicon diode when 500mA is flowing through it?

The forward voltage drop of a 1N4007 silicon diode with 500mA flowing through it is 0.832 volts.

How does the temperature of a diode relate to the heat generated?

The temperature of a diode increases with the heat generated, which is a product of the forward voltage drop and the current flowing through it.

What is the advantage of Schottky diodes in high-frequency applications?

Schottky diodes have very fast switching speeds, making them suitable for use at higher frequencies, such as those found in switch mode power supplies.

Why might one choose to use a silicon diode over a Schottky diode?

One might choose to use a silicon diode over a Schottky diode due to its lower reverse leakage current, which can be significant in certain applications like peak detector circuits.

What is reverse leakage current and how does it differ between silicon and Schottky diodes?

Reverse leakage current is the small current that flows backward through a diode when it is reverse-biased. Silicon diodes have a much lower reverse leakage current compared to Schottky diodes.

How does the forward voltage drop correlate with the maximum voltage rating of a diode?

The forward voltage drop tends to be lower for diodes with higher maximum voltage ratings. However, choosing a diode with a higher voltage rating than necessary can sacrifice efficiency.

What is the practical implication of choosing a diode with a higher voltage rating than needed?

Choosing a diode with a higher voltage rating than the peak reverse voltage can lead to reduced efficiency due to a higher forward voltage drop.

Outlines

00:00

🔌 Introduction to Schottky Diodes

This paragraph introduces Schottky diodes, comparing them to regular silicon diodes and highlighting their unique circuit symbol. It emphasizes the importance of recognizing the differences in behavior despite their similar appearance. The narrator reviews basic diode concepts, such as unidirectional current flow and the forward voltage drop (Vf), which causes heat generation. The example given illustrates the lower Vf of a Schottky diode (0.345V) compared to a silicon diode (0.832V), resulting in less heat and a cooler operating temperature. The paragraph also mentions that Schottky diodes are more efficient for blocking reverse current and have fast switching speeds, making them suitable for high-frequency applications. A demonstration compares the rectification capabilities of both diodes at 60Hz and 300kHz, showing the Schottky diode's superior performance at higher frequencies.

05:01

🔋 Considerations for Using Schottky Diodes

The second paragraph discusses the reverse leakage current of diodes, which is a small amount of current that flows against the intended direction. It contrasts the minimal reverse leakage current of a silicon diode with the significantly higher leakage current of a Schottky diode, which can be problematic in certain applications like peak detector circuits. The narrator advises that while Schottky diodes have advantages, they are not universally suitable due to their higher leakage current. The paragraph concludes with a tip on selecting diodes based on their forward voltage drop in relation to the maximum voltage rating, suggesting a balance between safety margin and efficiency.

Keywords

💡Schottky Diodes

Schottky diodes are a type of semiconductor diode with a low forward voltage drop and rapid switching capabilities. They are distinct from regular silicon diodes due to their unique construction and properties. In the video, the presenter compares Schottky diodes to silicon diodes, highlighting their lower forward voltage drop, which results in less heat generation and higher efficiency. An example given is comparing the heat generated by a silicon diode (416 mW) to that of a Schottky diode (173 mW) under the same current conditions.

💡Forward Voltage Drop (Vf)

The forward voltage drop, or Vf, is the voltage that appears across a diode when current flows through it in the forward direction. It is a fundamental concept in diode operation and is used to calculate the power dissipation within the diode. The video emphasizes that Schottky diodes have a lower Vf compared to silicon diodes, which contributes to their lower heat generation and higher efficiency. The example given is a silicon diode with a Vf of 0.832 volts versus a Schottky diode with a Vf of 0.345 volts under the same current.

💡Heat Generation

Heat generation in diodes is a byproduct of their operation, resulting from the power dissipation due to the forward voltage drop and current flow. The video script explains that Schottky diodes generate less heat than silicon diodes because of their lower forward voltage drop. This is illustrated by calculating the heat generated by a silicon diode (416 mW) versus a Schottky diode (173 mW) under identical current conditions.

💡Efficiency

Efficiency in the context of diodes refers to their ability to conduct current with minimal power loss, usually in the form of heat. The video discusses how Schottky diodes are more efficient than silicon diodes due to their lower forward voltage drop, which leads to less heat generation and thus, more efficient current conduction.

💡Switching Speed

Switching speed is the rate at which a diode can transition from allowing forward current to blocking reverse current. The video highlights that Schottky diodes have faster switching speeds compared to silicon diodes, making them suitable for high-frequency applications. An experiment in the video demonstrates this by comparing the performance of silicon and Schottky diodes at a 60Hz sine wave and then at a much higher frequency of 300kHz.

💡Frequency

Frequency refers to the number of cycles per second in an alternating current (AC) signal. In the context of the video, frequency is important when discussing the performance of diodes, particularly Schottky diodes, which are capable of operating at higher frequencies without significant degradation in performance. The video contrasts the performance of silicon and Schottky diodes at 60Hz and 300kHz to illustrate this point.

💡Rectification

Rectification is the process of converting alternating current (AC) to direct current (DC) by allowing current to flow in only one direction. The video uses the example of a half-wave rectification setup with both silicon and Schottky diodes to demonstrate how they block the negative half of a sine wave, resulting in positive voltage bumps.

💡Recovery Time

Recovery time is the time it takes for a diode to switch from the forward-biased state to the reverse-biased state. The video mentions that Schottky diodes have a quicker recovery time compared to silicon diodes, which is why they are often used in medium to high-frequency applications. The video suggests watching another video for a more in-depth understanding of diode recovery time.

💡Reverse Leakage Current

Reverse leakage current is the small amount of current that flows through a diode in the reverse direction when it is supposed to be blocking current flow. The video explains that Schottky diodes have a higher reverse leakage current compared to silicon diodes, which can be significant in certain applications such as peak detector circuits. The script provides an example where a silicon diode shows almost no reverse leakage current, while a Schottky diode shows around 20 microamps.

💡Voltage Rating

Voltage rating refers to the maximum voltage a diode can withstand before breaking down. The video script advises viewers to select a diode with a voltage rating slightly higher than the peak reverse voltage they expect in their application, rather than choosing the highest voltage rating available, as this could lead to reduced efficiency.

Highlights

Schottky diodes have a different circuit symbol compared to regular silicon diodes.

Schottky diodes only allow current to flow in one direction, similar to regular diodes.

The forward voltage drop (Vf) across a diode generates heat, calculated as Vf multiplied by current.

Schottky diodes have a lower forward voltage drop than silicon diodes, resulting in less heat generation.

A 1N4007 silicon diode with 500mA current results in 416 mW of heat at 54 degrees temperature.

A 1N5817 schottky diode with the same current results in only 173 mW of heat at 38 degrees temperature.

Schottky diodes are more efficient at blocking reverse current flow compared to silicon diodes.

The forward voltage (Vf) of a schottky diode can be found from the datasheet and varies with current.

Temperature affects the forward voltage drop of schottky diodes.

Schottky diodes have fast switching speeds, making them suitable for high-frequency applications.

At 60Hz, both silicon and schottky diodes can effectively rectify a sine wave.

At 300kHz, schottky diodes handle high-frequency input better than silicon diodes.

Schottky diodes are quick, making them ideal for medium to high-frequency applications.

Silicon diodes have a very low reverse leakage current, which is almost unmeasurably small.

Schottky diodes have a higher reverse leakage current compared to silicon diodes.

The reverse leakage current of schottky diodes can be significant in certain circuits, such as peak detectors.

The forward voltage drop of a diode tends to correlate with its maximum voltage rating.

It's recommended to choose a diode rated for about 10 volts more than the peak reverse voltage required.

Transcripts

In this video I'm going to teach you about schottky diodes. They are very similar to

regular silicon diodes, but with some important differences.

For starters, they have a different circuit symbol.

Notice how similar they look to other diodes - make sure you don't get them

confused because they behave very differently! Okay, before I talk about what is special

about schottky diodes I want to remind you of some basic

diode concepts. In my previous video about diodes we talked about how they only let current

flow in one direction, and when current is flowing

through the diode, there is a voltage drop across the diode

called the forward voltage drop... or "Vf". Since you have a drop in voltage across a

device, and there's current flowing through it, you end up with some

heat being generated in the diode. And here's the equation for that - Vf multiplied by the

current gives the power in watts.

One of the main schottky diode advantages is that they have a lower Vf than silicon

diodes. This results in less heat being generated. Let

me show you an example. Here I have a regular 1N4007 silicon diode

with 500mA flowing through it. If I measure the voltage drop

across the diode it's 0.832 volts. 0.5 Amps multiplied by 0.832 Volts gives 416 mW of

heat. And that's causing the diode

to have a temperature of 54 degrees. Now let's try the same experiment with a 1N5817

schottky diode. We've got the same 500mA flowing through it, but the forward voltage drop is

only 0.345 volts instead of 0.832 volts! 0.5 amps multiplied

by 0.345 volts gives 173 mW of heat instead of the 416 mW we were getting with the silicon

diode. This results in a lower temperature of 38

degrees instead of 54 degrees. So basically schottky diodes are a more efficient

way to block the reverse flow of current. You can always find out the Vf of a schottky

diode from the datasheet. Make sure you check out the

graph of Vf versus current, because the forward voltage is going to change depending on

the current.

The temperature affects it too! Ok, are there any other advantages of schottkys?

Well, they tend to have very fast switching speeds, so you can use them at higher frequencies.

I have a demo set up here where I am generating a

60Hz sine wave, and I am feeding it into two different

types of diodes - a 1N4007 silicon diode and a 1N5817 schottky diode. These diodes are

very common and I'm just using a couple of resistors for

loads.

Okay, let me explain what you are seeing here. In yellow, we have the input sine wave. It's

not a perfect sine wave because I'm putting an unusual

load on my waveform generator with the multiple diodes and resistors. In green, the silicon

diode is blocking off the negative half of the sine wave. We

are successfully doing half wave rectification, which gives us these positive voltage bumps.

In blue, the schottky diode is also doing a great job,

and as you would expect, there's less of a voltage drop. All of

this is happening at 60Hz, which is a frequency that both diodes are designed to be used with.

So what happens if we increase the frequency of the input sine wave to 300kHz? That's a

frequency you'd expect to see in a switch mode power

supply. Woah! What's the matter? It's like the schottky

diode is on steroids and the silicon diode has been

pushing too many pencils. The schottky diode has no trouble with the

higher frequency, and successfully prevents the reverse

flow of current. But the silicon diode is doing a terrible job of rectification. In

every cycle, it's spending a lot of time allowing current to flow backwards,

before finally blocking it off. Every diode takes a

certain amount of time to switch from allowing forward current, to blocking reverse current.

Schottky diodes tend to be very quick, so that's why

they are often used in medium to high frequency applications.

If you want to learn more about this behavior and how to accurately measure the recovery

time of a diode, enable annotations and check out Alan's

excellent video on the subject. Okay, so if schottky diodes are quick and

efficient, why doesn't everyone use them all the time? Why

would you ever use a silicon diode? To answer that, I have to talk about another

property of diodes, called the reverse leakage current.

You know how diodes block the reverse flow of direct current? Well... that's not 100%

true. There's a small leak. Check this out. I have a power

supply set to 19 volts, and that's connected to a silicon diode

that is backwards. It's in series with my multimeter, so I am measuring the amount of

current that is flowing backwards through the diode. As you

can see, the reverse leakage current is almost unmeasurably small. That's what you want to

see for a perfect diode. Now let's try the same

experiment with the schottky diode. You can see that with -19V across it, there's

almost 20 microamps of reverse current flow. That's a LOT

more than the silicon diode. Now you might be thinking that 20 microamps is not a big

deal, and if you're using a diode for reverse voltage protection,

it's not a big deal. But if you are using a diode as

part of something like a peak detector circuit, that 20uA could be significant. And across

the whole temperature range of the diode, the leakage

current can reach well into the milliamps! So you can't

just blindly use schottkys everywhere. Now there's one last thing I want you to know

about diodes, and not many people realize this. The

forward voltage drop tends to correlate with the maximum voltage rating on the diode.

When searching for diodes you might be tempted to go out and buy the diode with the highest

voltage rating possible because you'd have a larger safety margin. Well, you can do that,

but you'd be sacrificing efficiency. Try figure out what

your peak reverse voltage is, and pick a diode that's rated for

about 10 volts more than that. But make sure you figure it out accurately, otherwise...

Thank you for watching! Make sure you check out my other videos about electronics.