I prefer using PNP transistors over NPN because it feels more intuitive to control the positive DC voltage instead of the negative. It can be challenging to ensure you are using the correct components and avoiding NPN transistors. This becomes crucial when the negative DC is grounded, as it can lead to control problems. Unlike AC voltage, where the neutral is never switched, using PNP transistors for DC applications can help avoid potential issues with control and grounding.
During my time working in hazardous environments, we relied on NPN in order to reduce the risk of sparks when shorting out the sourcing input. In the event of a short, only an input is received. The same principle applies to sinking outputs, providing a safer option in explosive areas.
In the realm of control systems, there is a blend of various methods influenced by different countries' standards merging together. This often leads to a situation where outdated practices persist, despite the availability of more efficient options. The concept of "high side switching" in AC control systems, for instance, was initially adopted without much consideration for its compatibility with DC controls and transistors. This has resulted in the need for additional components like charge pumps for PNP/P-MOS transistors, making low-side switching with NPN/N-MOS transistors a more straightforward option. While the price gap between these options has narrowed over time, historical cost considerations may have favored NPN transistors in the past.
It's true that NPN components used to be more affordable in the past. This was something I learned while studying electronics in the late 1980s. Even back then, the increasing cost of NPN transistors was starting to raise eyebrows.
NPN transistors are commonly used in electronics, especially in historical applications before the rise of PLCs. When it comes to PLC inputs, it is often preferred to use sink rather than source to prevent false triggering. This is because spikes in the voltage are usually positive, making it unlikely to cause a change in input signals when using sink configuration. For example, if a PNP source is used and a spike occurs, it may not be detected as an input change if the switching point is set at 24V. However, with a sink configuration, setting the switching point at 8V allows for better detection of spikes, such as a 10-12v spike triggering the input. In my experience of over 40 years in PLC programming, I have only encountered false triggering once. By changing the input card to sink configuration, the issue was resolved.
According to NetNathan, PNP technology (source) is preferred due to its natural feel. Conversely, individuals accustomed to NPN technology may find PNP to be unconventional or "weird." This preference for PNP over NPN may be influenced by one's familiarity with the technology standard in their workplace.
I understand your perspective, however, it's also worth noting that NPN transistors are generally faster and exhibit better performance in high-frequency applications due to lower saturation voltages. Nonetheless, both PNP and NPN transistors have their pros and cons, and it often comes down to specific application needs that would determine which is more suited. Despite your preference, considering NPN transistors in certain scenarios could offer substantial benefits.
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Answer: 1. Why would someone prefer using PNP transistors in DC applications over NPN transistors? - The preference for PNP transistors in DC applications may stem from the intuitive control of positive DC voltage instead of negative, especially when negative DC is grounded.
Answer: - Ensuring the correct components are used and avoiding NPN transistors is crucial in DC applications, particularly when negative DC is grounded, to prevent control problems.
Answer: - Using PNP transistors in DC applications can help avoid potential issues with control and grounding, similar to how neutral is never switched in AC voltage, thereby providing more stability in the circuit.
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