Why doesn't capacitor voltage and inductor current allow sudden changes?

We all know that capacitor voltages cannot change abruptly and inductor currents cannot change abruptly, what is the theoretical basis for this?

Take an example of an RC first-order low-pass filter.

Vin charges capacitor C1 through the R1 resistor, the potential of Vin is added to the two metal pole plates of capacitor C. The positive and negative charges are gathered towards the two-pole plates of the capacitor respectively under the effect of the potential difference and an electric field is formed, which is the charging process of the capacitor.

Charging of capacitors

The charge number, which measures the charge of a capacitor, is Q，Q = CV and C is a constant, so the charge number is proportional to the voltage.

C = Q/V, the capacity represents the ability of the capacitor to store charge and the differential expression is：

Current is the amount of change in the number of charges per unit of time：

Combining the two equations (1) and (2) yields：

It follows from the formula that： the amount of change in current and voltage across a capacitor is proportional, or the amount of change in voltage across a capacitor is proportional to the current.

It is assumed that the voltage of the capacitor can change abruptly, i.e. an infinite current is required. In practice there is no infinite current, i.e. the voltage cannot change abruptly.

Let's look at why inductor currents cannot change abruptly？

The sum of the fluxes in each turn of an inductor coil is called the chain Ψ and measures how much of the inductor coil is magnetized.

The magnetic chain is proportional to the current, the higher the current, the more the inductor coil is charged with the magnetic chain, i.e. Ψ = L*I, for a given inductor coil, L is a constant.

L = Ψ/I, the inductance represents the electromagnetic conversion capacity of the inductor coil and the differential expression is：

According to the principle of electromagnetic induction, a change in the magnetic chain produces an induced voltage, the greater the change in the chain the higher the induced voltage, i.e：

Combining the two equations (1) and (2) yields：

It can be seen from the formula: the rate of change of inductor voltage and current are proportional, or the rate of change of current and inductor voltage are proportional.

The assumption that the inductor current can change abruptly, i.e. that an infinite voltage is required, also does not exist in practice, i.e. the inductor current cannot change abruptly.

Comments

The biggest problem with the latest 56 semiconductor manufacturers suspend orders, price increased, and long lead time. How can you fix it?

Following the suspension of MCU orders by ELAN , Holtek Semiconductor issued a notice on 21st April suspending orders with immediate effect. The price of various semiconductors, especially MCUs, has risen as a result of factors such as the tightness of 8-inch wafer foundries. The demand for MCUs is so high that many major MCU manufacturers at home and abroad are operating at full capacity, but supply still exceeds demand. In its notice, Holtek Semiconductor stated that Suspension of orders for 2022 Subject: Orders with delivery dates in 2022 are suspended with immediate effect. Description: 1. The wafer fabs and packaging houses have advised that there will be another wave of price increases soon - price increases of 15%-30%. 2. The fabs are expected to provide 2022 production numbers by early May and will announce 2022 order acceptance rules when confirmed. 3. expected to resume accepting orders for 2022 by mid-May. 4. 2022 orders that have received deposits will be rescheduled

Understanding of DC-DC buck bootstrap circuit

In the peripheral circuit design of DC-DC BUCK chips, we usually add capacitors or a combination of capacitors + resistors between the BOOT and SW pins, this piece of circuit is called bootstrap circuit, the capacitors and resistors in the bootstrap circuit are called bootstrap capacitors and bootstrap resistors. What is a bootstrap capacitor? DCDC Buck chip has a pin called BOOT, and some are called BST. The following is an explanation of the BOOT pin of a DCDC chip. In the external circuit design, a capacitor, generally 0.1uF, is needed between the BOOT and SW pin, and is connected to the driver end of the high-end MOS tube of DCDC. How does a bootstrap capacitor work? The following is a block diagram of a DCDC BUCK chip, the top NMOS is called the high-side MOSFET and the bottom NMOS is called the low-side MOSFET. When the high side MOS tube is turned on, SW is VIN, SW charges and stores energy in the inductor, and the inductor current is rising; when the low side MOS

2022 global chip shortage continues: ST、NXP、ADI、XILINX、ONSEMI、DIODES... latest trends

Under the influence of the epidemic and various emergencies around the world, the global chip industry fell into a shortage of stock in 2021. Now it has been a year, and the shortage of chips seems to have not eased. Below, we have collated the latest market developments of the original chip manufacturers such as ST, Renesas, NXP, ADI, ON Semiconductor, Microchip, Qualcomm, etc., so that you can have a good idea of the market situation. ST: Large shortage of high-end products and automotive chips Most stockists have been selling off since the prices of ST products have fallen back, but this month has seen a small rebound. For example, STM8S003F3P6TR and STM32F103VCT6 , two pieces of material, have seen a small price increase. It is worth noting that the market price of ST's brake system chips has recently soared, and other automotive chips have also risen, and there is still a large shortage of high-end products and automotive chips, and delivery times are still long. In additi

Teach you 5 ways to identify and avoid counterfeit electronic components in a second

In the process of purchasing electronic components, the most worrying thing for buyers is not the price, but the quality of the product. There are a variety of IC chips on the market, of all kinds, and without paying attention to the distinction, it is sometimes difficult to see the difference between various materials, whether it is true or false, new or refurbished. The following is a compilation of some methods to identify genuine and fake chips, for your reference. Common chip counterfeiting methods Material A counterfeit material A Original manufacturer's tailor loose material: the original packaging has been disassembled or is no longer available, but product functionality and yield may be lower due to storage time or handling process, etc. Original manufacturer scrap or defective products: mainly products that have not passed factory inspection by the original manufacturer, such as scrap products after reliability testing, poor packaging quality, bad test products, etc. Orig

9 effective ways to improve your electronic components specification for approval

1. Let purchasers find manufacturers to provide specifications, safety information, environmental protection information, insurance information - E-document 2. Verify that the information is true and complete, such as the applicable period of the document, so as not to be fooled by the manufacturer. 3. Let the buyer find the manufacturer to provide samples, specifications, safety information, environmental information, insurance information - Paper files 4. Environmental test: send several samples to the environmental laboratory for ROSH halogen test. 5. Electrical specifications and high-temperature testing - e.g. electrolytic capacitors : A: measuring capacity and deviation withstand voltage, PIN foot tin is good B: go through the production line to see if the capacitors are deformed after the high temperature of the furnace and if the capacity and the deviation voltage are okay. 6. Body size check - e.g. electrolytic capacitors . Body height and diameter, PIN pin spacing, PIN pin d

Seektronics

Search This Blog