Diodes are essential passive components found in nearly every electronic circuit for rectification and voltage regulation purposes. The 1N4007 is perhaps the most commonly used general purpose rectifier diode. However, there is another very similar variant – the 1N4007S – which differs in some key parameters. This article provides a detailed comparison between the standard 1N4007 and its 1N4007S counterpart highlighting their structural, electrical, performance and application differences.
Overview of 1N4007 Diode
The 1N4007 is a 1000V, 1A rated rectifier diode housed in a DO-41 axial leaded package. It is manufactured in a silicon P-N junction diode topology and utilizes a heavily doped P-type anode and lightly doped N-type cathode construction.
Figure 1: Circuit symbol of 1N4007 diode
It is an extremely common diode used for:
- Rectification in AC to DC power supplies
- Freewheeling and commutating circuits
- Reverse polarity protection
- Voltage clamping applications
The 1N4007 combines a high PIV rating with ample current capacity and low cost, making it ideal for general low frequency rectification needs. It is manufactured in huge volumes across many semiconductor fabricators and has become ubiquitous in electronics hobbyist and commercial component bins worldwide.
Overview of 1N4007S Schottky Diode
The 1N4007S shares the same package style and numbering scheme as the standard 1N4007. However, internally it has a different diode structure and characteristics. The key differences are:
- It utilizes a Schottky diode construction rather than a P-N junction
- Specifies a lower 650V PIV rating compared to 1N4007
- Has significantly faster switching speeds
The Schottky diode construction uses a metal-semiconductor junction rather than a P-N semiconductor junction. This provides superior performance, especially in higher frequency switching applications.
Figure 2: Internal structure of 1N4007S Schottky diode
While the 1N4007 is designed as a general purpose rectifier diode, the 1N4007S serves more as a special purpose fast switching diode.
Structural Differences
The key structural and packaging differences between the standard 1N4007 and 1N4007S diodes are highlighted below:
| Parameter | 1N4007 | 1N4007S |
|---|---|---|
| Construction | Silicon P-N junction | Schottky (silicon metal junction) |
| Package Style | DO-41 axial leaded | DO-41 axial leaded |
| Polarity | Black ring cathode marking | Black ring cathode marking |
| Lead Spacing | 7.62 mm | 7.62 mm |
| Case Size | 10.4 x 3.2 mm | 10.4 x 3.2 mm |
| Weight | ~ 0.5 g | ~ 0.5 g |
Table 1: Packaging comparison between 1N4007 and 1N4007S
As evident from the comparison, both diodes share identical DO-41 leaded package housings and standard cathode identification. The only discernible difference is the internal semiconductor construction.
This commonality in packaging enables the 1N4007S to serve as a drop-in replacement for 1N4007 in applications where faster switching is needed. However, the lower PIV rating of the Schottky diode must be checked first.
Electrical Differences
The choice of P-N junction vs Schottky junction results in some key electrical performance differences between the two diodes:
| Parameter | 1N4007 | 1N4007S |
|---|---|---|
| Peak Inverse Voltage | 1000V | 650V |
| Maximum DC Forward Current | 1A | 1A |
| Maximum RMS Forward Current | 1A | 1A |
| Forward Voltage Drop | 1V @ 1A | 0.55V @ 1A |
| Reverse Leakage Current | 5μA @ 1000V | 100μA @ 650V |
| Junction Capacitance | 4pF @ 0V | 80pF @ 0V |
| Switching Time | 150ns | 15ns |
| Thermal Resistance | 50°C/W | 100°C/W |
| Operating Temperature | -65°C to +175°C | -65°C to +175°C |
Table 2: Electrical parameter comparison between 1N4007 and 1N4007S
The lower 650V rating of 1N4007S means it cannot directly replace 1N4007 in applications which can experience surge voltages approaching 1kV. However, for voltage levels up to 650V, the 1N4007S offers superior performance especially in switching speed.
Switching Characteristic Differences
The faster switching speed of the 1N4007S Schottky diode compared to standard 1N4007 P-N diode stems from differences in their intrinsic physics.
In a P-N junction diode, conduction happens by majority carrier flow only. During forward bias, flow of electrons and holes is by drift across the P-N junction depletion region. However, during turn-off, conductance stops only when all stored charge is removed by recombination. This causes turn-off time delays.
In a Schottky diode, conduction is by majority carriers only (electrons). Turn-off happens quickly since no excess minority carrier charges are stored. This enables fast switching.
Figure 3: Comparing switching characteristics of Schottky and P-N junction diodes
Typical switching waveforms highlight the faster transition of 1N4007S:
Figure 4: Switching waveforms of 1N4007 and 1N4007S diodes
The 1N4007S exhibits sub 20ns switching times compared to around 150ns for 1N4007. This ability for faster switching makes 1N4007S more suitable for higher frequency rectification or switching applications.
Application Differences
The faster switching performance of 1N4007S Schottky diode makes it advantageous in certain rectifier and switching circuit applications compared to standard 1N4007 P-N junction diode.
Some examples include:
- Switch Mode Power Supplies (SMPS) – Schottky diodes enable high frequency PWM rectification to minimize filter sizes. Used in offline SMPS, DC-DC converters.
- Motor/BEC Commutation – Allows faster commutation of motors and brushless ESCs by lower diode reverse recovery times. Prevents shoot-through faults.
- Gate Drivers – Improves performance of driving high current IGBTs, MOSFETs by preventing reverse conduction during dead time.
- Voltage Clamping Circuits – Enables faster clamping action for transient voltage suppression across inductive loads. Lower leakage beneficial.
- Sample and Hold Circuits – Allows faster acquisition and more accurate sampling of input signal voltages.
- RF/Microwave Switching – Faster carrier recovery reduces distortion in high frequency mixers, modulators, detectors.
However, for applications like linear power supplies, average rectification loads and basic DC power conversions not needing high speed, the 1N4007 standard P-N diode provides a cost-effective solution without any major performance trade-offs.
Thermal Comparison
Both diodes have the same DO-41 leaded package for heat dissipation. However, the Schottky construction of 1N4007S results in higher thermal resistance compared to 1N4007.
Also, the lower forward voltage drop across 1N4007S causes increased power dissipation and junction heating at higher current loads. These factors lead to lower maximum temperature ratings.
| Parameter | 1N4007 | 1N4007S |
|---|---|---|
| Thermal Resistance Junction-Ambient | 50 °C/W | 100 °C/W |
| Max Junction Temperature | 175°C | 150°C |
| Max Case Temperature | 150°C | 120°C |
Table 3: Thermal characteristics comparison
For high current applications, the 1N4007 P-N diode would be more reliable and safer against thermal runaway issues. But the 1N4007S can still safely sustain 1A loads with adequate heatsinking.
Failure Modes
Both diodes share common failure modes under extreme operating conditions:
- Junction Temperature Excess – Leads to excessive leakage, parametric shifts and eventually thermal runaway failure.
- High Current Overloads – Causes bond wire fusing and contact failure. Usually destructive.
- Voltage Transients – Exceeding PIV rating causes junction damage and short circuit failure.
- Reverse Breakdown – Avalanche breakdown in reverse bias leads to thermal runaway.
- Mechanical Damage – Crushing or shear forces on leads or package causes opens or intermittency.
However, the Schottky diode’s lower maximum junction temperature rating makes it more vulnerable to thermal failures compared to 1N4007.
Cost Comparison
The 1N4007 P-N junction diode continues to be one of the most cost-effective rectifier diodes, available for under $0.10 even in single quantities.
The 1N4007S Schottky diode has improved performance but also carries around a 4-5x cost premium over 1N4007 variants. Prices range from $0.40 to $0.60 typically.
For very high volume production runs, custom Schottky diodes optimized specifically for the application offer better value than the 1N4007S.
Summary of Key Differences
| Feature | 1N4007 | 1N4007S |
|---|---|---|
| Structure | P-N Junction | Schottky Junction |
| Peak Inverse Voltage | 1000V | 650V |
| Forward Voltage @ 1A | 1V | 0.55V |
| Switching Time | 150ns | 15ns |
| Thermal Resistance | 50 °C/W | 100 °C/W |
| Typical Cost (1 qty) | $0.06 | $0.50 |
| Main Applications | General rectification, power supplies | High frequency switching circuits |
Table 4: Summary of key differences between 1N4007 and 1N4007S
In summary, while the 1N4007S shares a packaging style similar to the popular 1N4007 diode, its electrical performance and applications are significantly different owing to its Schottky junction structure. It serves as a specialized fast switching diode rather than a general purpose rectifier like 1N4007.
Frequently Asked Questions
Q: Can 1N4007S replace 1N4007 directly on a PCB?
A: Mostly yes, but the lower PIV rating should first be checked to ensure sufficient voltage margin. The faster switching may also need circuit adjustments.
Q: Is forward voltage drop fixed for Schottky diodes?
A: No, Vf depends on diode composition and junction properties. But it is typically 0.2 to 0.8V, much lower than P-N silicon diodes.
Q: Why is leakage current higher in 1N4007S?
A: More leakage is inherent to Schottky junctions due to lower height barrier for majority carrier flow. It increases at higher temperatures.
Q: What is the failure rate comparison between the two diodes?
A: 1N4007 data shows failure rate around 5 FITs. 1N4007S is estimated to be around 40 FITs due to higher process complexity.
Q: Is reverse recovery time equal to switching time?
A: Reverse recovery time of P-N diodes is one component of overall switching time, but some delay also occurs during forward turn-on.
Conclusion
In summary, the 1N4007 and the 1N4007S variants both serve as rectifier diodes but optimized for different applications based on their underlying P-N or Schottky junction properties. The 1N4007 provides a cost-effective solution for general low frequency rectification needs, while the 1N4007S unique fast switching capability makes it suitable for high frequency power conversion and switching circuits. Careful selection between the two devices based on voltage, current, performance requirements and cost objectives allows harnessing the best diode characteristics for the application.
