What is a schottky diode?
Summary
TLDRThis 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
🔌 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.
🔋 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.
Mindmap
Keywords
💡Schottky Diodes
💡Forward Voltage Drop (Vf)
💡Heat Generation
💡Efficiency
💡Switching Speed
💡Frequency
💡Rectification
💡Recovery Time
💡Reverse Leakage Current
💡Voltage Rating
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.
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