FAQ:
Why is there an initial inrush current spike when turning on the power supply that is connected to my N3300 series electronic load?
Source turn-on is defined as having a rapid change in input voltage from no current draw to some operating voltage which allows the load to draw the programmed current. During this sudden source turn-on, the load will draw more current than it is set for because of the following reasons.
1. There is an input snubber network that helps stabilize the load across all operating conditions and modes. This snubber network is an RC series network between the plus and minus input terminals. The values are different for different load modules.
2. The second reason for the current in rush is that you are going from an unregulated conditions which is zero volts to the output voltage setting. When you program the load to draw current and there is no voltage on the input, the load starts to turn on the FET’s to try and draw the programmed current but since there is no voltage you cannot draw any current. The load detects this unregulated condition and leaves just one of the FET’s turned. Once voltage is applied by the external source, that one FET being turned on allows current to start flowing - thus allowing the load to start regulating the current through it. If you turn on the voltage source very rapidly, this applies a large dV/dt to the input of the load. Since the snubber network is discharged when you first apply the voltage, the capacitor looks like a short and the only thing limiting current is the resistor in series with the capacitor.
After a few microseconds have passed, the current limiting circuits of the load module will limit the input current to its programed setting.
Applies to: N3300A, N3301A, N3302A, N3303A, N3304A, N3305A, N3306A, N3307A
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