Episode 8 Column
Chapter 8 contains what we’d like to call the “final boss” of this comic book: “constant current.” For those of you reading this and thinking that we aren’t going deep enough; congratulations, you have a proficient understanding of constant current. However, there are many power supply users who, like Minami, who still feel a bit fuzzy about this concept. Why is that?
In standard programmable DC power supplies, there is usually a “constant voltage” and “constant current” mode where voltage is often prioritized, and the instrument operates in a constant voltage mode. At the beginning of our story, we introduced the early DC power supplies, where only constant voltage mode (voltage output settings) was available. You would set the voltage that your DUT (device under test) required, and flow as much current as your power supply could provide. Voltage is often compared to water pressure. You can comfortably compare high and low voltage (voltage behavior) to a water gun; squeeze the trigger tightly and water will blast out, but squeeze the trigger lightly and you will only get drips. In other words, the concept of voltage control (constant voltage), is relatively easy to grasp.
But what about “constant current”? Going back to the water example, the concept would be something like “maintaining a constant amount of water regardless of water pressure,” which is not something that we encounter often in our day-to-day. Of course, if you have a basic understanding of electronics, it’s not too difficult to draw a connection between voltage and current (resistance) with a circuit diagram and “Ohm’s Law,” and then realize why the load voltage drops when a power supply goes into constant current mode. But as you know, the use of any kind of circuit diagram (and equation for that matter) would go against the rules we initially set when making this comic. So how did we go about it? Rather than explaining “constant current” operational theory, we decided to focus instead on the background behind it. There are many things in this world that you can utilize effectively even if you don’t truly comprehend them, as long as you can appreciate why they were concepted and what their potential benefits are (as well as intentions and reasons for them). This also holds true with DC power supplies. This means that understanding why constant current control is necessary as well as the advantages of it will serve as an effective outline for using DC power supplies correctly.
In other words, please don’t worry if you don’t deeply understand the theories throughout this comic. It’s all about familiarity! Think of it as like learning how to back up your car. When you first get your license, you feel a disconnect between the direction you want to move (direction of the steering wheel) and the direction that the car actually turns. However, once you have some experience under your belt, it becomes easy. This same principle applies to DC power supply operation modes. As you gain experience using the instrument, you slowly begin to understand key points (such as conditions and settings that affect the voltage and current, etc.). We believe that the chart (Important Points When Operating in Constant Voltage – Constant Current) on page 15 will prove particularly useful. Please try and memorize these points!