Identifying Parasitic Inductance and AC Step Responses скачать в хорошем качестве

Identifying Parasitic Inductance and AC Step Responses

Side-effects of parasitic impedances can cause signal glitches Click to subscribe: http://bit.ly/Scopes_Sub Scope tips eBook ► http://bit.ly/2MG_eBook ◄ Parasitic elements - parasitic inductance and parasitic capacitance - can cause some confusing glitches in your signals. What is a parasitic element? A parasitic element is a naturally occurring capacitance, inductance, or resistance that appears in non-ideal circuit elements. In this episode, we look at the simple capacitive circuit from the last 2-Minute Guru video:    • What is capacitance? The 3 Effects of Capa...   The circuit we are looking at is simply a capacitor connected to a square wave from the oscilloscope's function generator (WaveGen). A commenter noticed that there was a weird signal spike at the signal edge transitions. After doing some debugging, we were able to identify that the spike was a result of parasitic inductance in a jumper wire. To fully understand what's happening, we first have to understand how a capacitor responds to an step function and how an inductor responds to a step function. This understanding is essential to basic circuit theory and basic electronics. ( 1:14 ) A capacitor responds to a step function as a short circuit. At the instant the step function encounters capacitance, it can be modeled as a short circuit. As the capacitor begins to charge up, it transitions from a short circuit to an open circuit. After an effectively long time (infinitely long), the capacitor will completely charge and act as an open circuit. The rate at which a capacitor charges and discharges depends on the size of the capacitor (in Farads). In a simple circuit like the one in this video, the square wave acts as a step impulse, and the capacitor will charge or discharge to match the source voltage. An inductor responds to a step function as an open circuit. At the instant the step function encounters inductance, it can be modeled as an open circuit. As the inductor begins to charge up, it transitions from an open circuit to a short circuit. After an effectively long time, the inductor will completely charge and act as a short circuit. The rate at which an inductor charges and discharges depends on the size of the inductor (in Henries). In a simple inductive circuit, the square wave acts as the step impulse, and the inductor will charge or discharge to become a short circuit. ( 3:29 ) We then model the effective circuit, which is more than just a capacitor. The breadboard and the jumper wires have significant parasitic inductance. The inductance of the jumper connecting the waveform generator's square wave and the capacitor is the main source of the glitch. ( 4:05 ) When we evaluate how the circuit will respond to a rising edge from the waveform generator ( 5:02 ) Then, we plot what the ideal signal would look like. When the rising edge hits the inductance of the jumper wire, the inductor acts as an open circuit, and the signal measured by the oscilloscope will be the same as the source voltage. Since the inductor is small, it will charge very quickly and the measured voltage will drop. Once the inductor is charged, it will act as a short and begin to charge the capacitor. As the capacitor charges, the voltage measured by the oscilloscope will begin to rise. ( 6:08 ) Then, we look at how our circuit responds to a falling edge - which is exactly the inverse of how it responds to a rising edge. ( 7:30 ) Back to the oscilloscope. By probing the resistor that was in parallel with the capacitor, we were able to effectively probe just the capacitor without the jumpers. When probing the resistor, no glitch was present. When adding the jumpers back in, the glitch appeared again. ( 8:38 ) By probing just the capacitor without the breadboard or the jumper wires we can see that the glitch disappears almost completely. ( 9:30 ) Why isn't the spike the full height of the voltage source? Because the waveform generator isn't an ideal source, and the oscilloscope and acquisition system are not ideal. With an ideal source and infinite bandwidth the spike would jump to the full height of the voltage source. ( 10:15 ) The glitch can be made bigger by adding in an inductor in series with the waveform generator. ( 10:38 ) Because of parasitic inductance and parasitic capacitance, engineers have to be very careful when making measurements and when probing sensitive circuits. Capacitive loading and inductive loading can cause engineers to make misleading measurements. ( 11:02 ) Using a short ground lead, like the spring clips provided with many passive probes, will give much better measurements. More about Keysight oscilloscopes: http://bit.ly/SCOPES The digital storage oscilloscope we used: http://www.keysight.com/en/pcx-275955... (The Keysight InfiniiVision 1000 X-Series Oscilloscope) #parasitic #inductance #inductor #oscilloscope #capacitance #capacitor #ground #test #testing #electronics #engineering