Electronic devices are increasingly power-hungry. Consumers are demanding more functionality and features from everyday electronics. To meet this demand, engineers build devices that do more than ever before. These devices consume more power to fuel the new capabilities. Overvoltage (OV) and overcurrent (OC) are important security features in power supplies. Using these features lets you protect the device under test (DUT) from a higher voltage than the DUT’s design was meant to handle.
As the power capabilities of devices increase, the power required in test environments must also increase. You are likely to need a higher power in your DC power supplies for a wide variety of high-power test applications such as high-power DC-to-DC converters, batteries, uninterruptible power supplies, electric vehicles, and more.
Extra care is necessary when working with devices that use higher power, are reactive, or simply store energy. These devices are notorious for damaging themselves and the surrounding equipment. Fortunately, modern bench power supplies can protect against this damage.
Overvoltage and overcurrent protection
When working with high power, choosing a DC power supply that can protect the DUT when the voltage or current level exceeds a certain safety threshold is important. When the output exceeds a specific voltage or current level, the power supply must be able to recognize this event and properly disable the output. Overvoltage and overcurrent protection are two common features that can do this. It is critical to use these two features when working with high power. Overvoltage protects the device under test when the power supply exceeds the preset voltage limit. You can determine this preset voltage and program it on the front panel. When the power supply’s output exceeds the preset voltage limit, it disables the output, and an overvoltage indicator will appear. By default, overvoltage protection is typically always on unless specified otherwise. By default, most power supplies ship in that state from the factory. Make sure to set and turn on your overvoltage protection limit as a safety feature in your test setup.
Power supplies also have an overcurrent protection feature that works in a similar manner. Instead of monitoring voltage, overcurrent protection monitors the current that flows out of a power supply and disables the output if the current exceeds a certain present threshold. It does this in a slightly different way than that of overvoltage protection.
The preset over-current protection limit is the current limit setting itself. Once the current flowing through a power supply reaches the current limit setting, it enters into a constant current operating mode. The voltage usually goes down in constant current mode, and the current remains at the current limit setting. If
overcurrent protection is enabled; it will shut down the output to prevent too much current from flowing out. Typically, overcurrent protection is always off by default, and it is in that state when shipped from the factory. When necessary, use the overcurrent protection feature to safeguard your setup.
Protect Your Device Against Overpower
Overvoltage and overcurrent protection works well for protecting a device that has a single maximum voltage and current — some devices’ maximum current changes with the voltage. An example is a DC-to-DC converter, as its input can accept a range of voltages, and it provides a regulated voltage output. Every DC-to-DC converter has a maximum power rating. An increase in voltage will cause the max current to decrease. For example, take a 12 V to 19 V / 2 A converter that can handle a 9 V to 18 V input.
A power supply can test the input 9 V to 18 V, but the maximum current limit needs to be set independently for each voltage step, A current acceptable with a 9 V input would be damaging at 17 V, so the current limit needs to vary with the input voltage, as shown in Table 1. The max input power is set at 50 W to handle the inefficiencies and transient currents.
Table 1. Reducing the maximum current as voltage increases protects the converter from overpowering
Power supplies, like the Keysight E36200 Series autoranging power supply, support output LISTs. Output LISTs enable you to vary the output with a series of steps. Each step defines a voltage-current combination along with a dwell time and synchronizing triggers. A dwell time holds each step for the specified period before advancing to the next step.
With the power supply powering the converter in our example above, the output of the converter powers a 19 V, 2 A load.
Figure 2. An output LIST is a series of steps with an individual voltage, current, and dwell time
The power supply measures the actual voltage and current for each step and logs it. To characterize your device, multiply the actual voltage and current values and see how the power consumption changes. For this DC-to-DC converter, the input power is 44.8 W with an 8 V input, and 43.3 W with an 18 V input. We now have an accurate picture of our convertor’s performance.
LIST mode is useful for setting a series of voltage-current combinations and protecting a device from overpower.
Testing in a high-power environment introduces a set of new challenges. Overvoltage and overcurrent protection are important features for power supplies. It can protect your DUT from a voltage higher than the design was meant to handle. When it comes to power supplies, choose one with the necessary capabilities and safety features to meet your testing needs.