When to Use Custom Schottky diode protection Supplier？

Even better would be if someone could explain what I would be looking for as far as data sheet specs go so I can learn how to pick one myself in the future. I have a basic knowledge of electronics but I get lost when I read about forward voltage vs reverse voltage, leaked current vs rectified, recovery time, etc and how it would all relate to this and future projects I am working on.

First you think through what the various properties are. Sometimes it helps to write it out on paper (or whatever), especially when it's a new field for you or a complex problem, so let's do that:

• Forward voltage drop: The voltage loss across the diode when it's conducting. Varies with current. The reason people like Schottky diodes is that this type has low forward voltage drops. An "ideal" diode would have zero forward voltage drop.
• Reverse voltage: the maximum voltage you can apply to the diode in reverse polarity before it lets out the magic smoke. 
• Leakage current: when a diode is reverse biased, some current leaks through anyway. The smaller, the better.
• Rectified current: how much current the diode can pass comfortably before the manufacturer is no longer prepared to guarantee the magic smoke will stay in the part.
• Recovery time: how fast the transition from reverse to forward biased can be.

Then you think about what's important in your application. For power-ORing diodes, recovery time is usually totally insignificant. Reverse current is also usually not very important. Reverse voltage needs to be above the value of the highest power supply in the system (i.e., if you're ORing 12V and 5V, all the diodes better be rated 12V or higher!). You also need a bit of headroom; it's never good to run parts at 100% of their rating if it can be avoided. Your rectified current, as you've identified, should be 500mA minimum. (I might choose the next size up, 1A, Just In Case&#;. Or I might not, if I'm size-constrained on the layout or it's a non-critical part.) And then you can just pick the part with the lowest forward voltage drop that meets your other criteria of price, package size, availability, &c.

(Also consider what else you could use this part for; often it is better to buy two identical parts, even if they're individually a bit more expensive or somewhat overspecified, than managing two separate part inventories for different parts in different circuits. BOM line item reduction makes everyone happy!)

I adore manufacturer catalogs that list all their parts and relevant specs, because it makes this game a lot easier. NXP has a great MOSFET and diode catalog,

Sometimes if I need something a little more exotic, availability will be more limited. (That is not the case with bog-standard diodes.) In that case I usually start with the distributors' sites and see what they've got first, rather than what's in the catalog and might or might not be actually purchasable.

First you think through what the various properties are. Sometimes it helps to write it out on paper (or whatever), especially when it's a new field for you or a complex problem, so let's do that:Then you think about what's important in your application. For power-ORing diodes, recovery time is usually totally insignificant. Reverse current is also usually not very important. Reverse voltage needs to be above the value of the highest power supply in the system (i.e., if you're ORing 12V and 5V, all the diodes better be rated 12V or higher!). You also need a bit of headroom; it's never good to run parts at 100% of their rating if it can be avoided. Your rectified current, as you've identified, should be 500mA minimum. (I might choose the next size up, 1A, Just In Case&#;. Or I might not, if I'm size-constrained on the layout or it's a non-critical part.) And then you can just pick the part with the lowest forward voltage drop that meets your other criteria of price, package size, availability, &c.(Also consider what else you could use this part for; often it is better to buy two identical parts, even if they're individually a bit more expensive or somewhat overspecified, than managing two separate part inventories for different parts in different circuits. BOM line item reduction makes everyone happy!)I adore manufacturer catalogs that list all their parts and relevant specs, because it makes this game a lot easier. NXP has a great MOSFET and diode catalog, available here , and guess what? I pick NXP diodes a lot more often than other manufacturers'. (HINT FOR MANUFACTURERS: make my life easier and I'll buy your parts!) If you load that up and scroll to around page 36 (PDF page 20 because they paginated it bizarrely), you'll see a whole bunch of candidate parts. Many would probably work for your application. PMEGEJ looks like a decent starting point, but you may prefer to optimize for other things (smaller, higher power, better available, etc.) I usually pick a couple of favorites that look good, then search DigiKey, Mouser, or Octopart and see how available and expensive each is, and then just pick one.Sometimes if I need something a little more exotic, availability will be more limited. (That is not the case with bog-standard diodes.) In that case I usually start with the distributors' sites and see what they've got first, rather than what's in the catalog and might or might not be actually purchasable.

You will get efficient and thoughtful service from Hornby Electronic.

Power conversion schemes can be straightforward, such as with a set of diodes and a smoothing capacitor, or involving complex integrated circuits with multiple power conversion and regulation stages. However, one component can participate in all these areas and other important applications like radio frequency tuning and ESD protection: the Schottky barrier rectifier. These provide many important functions in electronics thanks to their internal structure and, of course, the Schottky effect.

If you need a diode for rectification that admits current with low forward voltage and fast switching speed, then a Schottky diode is the standard option. These characteristics make Schottky barrier rectifiers useful in power delivery to wave shaping applications. In this article, we&#;ll look at how these components stack up to their p-n diode cousins and when you might best be served using a Schottky barrier rectifier instead.

About Schottky Barrier Rectifiers

In the most basic sense, a Schottky barrier rectifier (or simply Schottky diode) operates in the same manner as a typical semiconductor diode made from Si or Ge. However, its primary purpose is to provide rectification, i.e., allow current to flow only easily along one specific direction. In this way, they are used in typical DC circuits to enable or block current or in AC circuits as part of wave shaping.

Structure

The major differences between a Schottky diode include their forward operating characteristics and, most importantly, their structure. Schottky diodes are constructed by depositing a metal electrical contact on a semiconductor; although n-type or p-type materials can be used in Schottky diodes, n-type materials are normally preferred. The reason is that p-type semiconductor Schottky diodes will have lower forward voltage and thus larger reverse bias breakdown current; using an n-type material provides the best balance between forward voltage and reverse bias current. On the other ends of the component, Ohmic contacts are placed to provide non-rectifying connections to the semiconductor.

Schottky barrier rectifier structure.

Advantages of Schottky Diodes

Compared to p-n junction diodes, Schottky barrier rectifiers have some advantages that make them more useful in switching, high-frequency rectification, and wave shaping applications. Some of the main advantages of Schottky diodes include:

• Narrow depletion region: When forward biased, a Schottky diode will have a smaller depletion region than in a p-n diode. As a result, the junction capacitance is very low, and a Schottky diode can be switched between forward and reverse biases very quickly.
• Lower forward voltage: A Schottky diode&#;s forward voltage is determined by its built-in voltage, which can be as low as 0.2 to 0.3 V. For comparison, Si p-n diodes have forward voltages of approximately 0.6 to 0.7 V, so they produce less current in forward bias.
• Low ideality factor: Schottky diodes tend to have low ideality factor, with values as low as 1.04 being common in commercially available components.
• Less noise: A Schottky diode will have lower nonlinear impedance in forward bias, producing less unwanted thermal noise than a typical p-n junction diode. This is one reason Schottky diodes are useful in microwave devices.

As shown below, the electrical advantages can be seen when comparing IV curves for a Si p-n diode and a Schottky diode. From here, we can see that the larger reverse bias current behavior leads to slower roll-off into the breakdown region, rather than fast avalanche behavior seen in a p-n diode.

IV curves (left) and forward voltage behavior (right) for Si p-n diodes and Schottky diodes.

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Typical Uses of Schottky Barrier Rectifiers

The three major application areas for Schottky barrier rectifiers include switching converters for power regulation, ESD protection, and in microwave circuits. Both applications place requirements on three specifications: the junction capacitance (determines the recovery time and frequency response), voltage limit, and current limit.

Power Conversion

In power systems, Schottky diodes are switched between forward bias and reverse bias in order to direct a DC current across an inductor and to the output of a regulator circuit. The diode needs to switch and fully modulate between the two states at the same rate as the driving PWM signal in the upstream switching power MOSFETs, which requires low junction capacitance. The other two important specifications are the voltage and current limits; the device should be able to provide rectification at the applied voltage during operation without entering breakdown.

Microwave Circuits

Schottky diodes can be used in microwave circuits that operate up to GHz frequencies in low-load conditions. The recovery time will be limited by the load impedance and the junction capacitance (see below for an example in a 1N Schottky diode). One big advantage of a Schottky diode in microwave circuits compared to a Si p-n diode is its linearity near zero bias, allowing oscillating signals to be collected directly, and without DC offset if needed.

 

Example junction capacitance in reverse bias for the Vishay 1N-E3/54.

ESD Protection

Certain low-voltage or slower transient events can be reliably protected against with Schottky diodes. An example is shown in the circuit diagram below. In this example, two Schottky diodes are placed as pull-up elements to a power rail in reverse bias. The low voltage drop of these diodes enables clamping of moderate currents in reverse bias back to ground from moderately strong ESD events. A very similar application is used in motor control or when driving large inductive loads; placing the Schottky diode parallel around the load in reverse bias will create the same effect and will protect the driver circuit from damage should a back EMF surge event occur. Should very high levels of ESD protection be needed, a good option is something like a gas discharge tube.

ESD protection with Schottky diodes.

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