• Latest
  • Trending
  • All
  • Capacitors
  • Resistors
  • Inductors
  • Filters
  • Fuses
  • Non-linear Passives
  • Applications
  • Integrated Passives
  • Oscillators
  • Passive Sensors
  • New Technologies
  • Aerospace & Defence
  • Automotive
  • Industrial
  • Market & Supply Chain
  • Medical
  • RF & Microwave
  • Telecommunication

Capacitors Pre-charging in Drive Circuits Using Pulse-Withstanding Resistors

21.7.2022

Jianghai Launches Four New Stacked Polymer Capacitor Series

21.7.2022

High Voltage MLCC for EV Powertrain

21.7.2022

Filter Q Factor Explained

21.7.2022

Würth Elektronik Introduces Snap-In Supercapacitors

20.7.2022

Skeleton to Build the World’s Largest Supercapacitor Factory

20.7.2022

Vishay Releases High Current, High Temperature Edge-Wound Inductors

19.7.2022

Murata Introduces Low DCR Power Over Coax Metal Alloy Chip Inductor

18.7.2022

Film Capacitor Failures Deep Dive Case Study

18.7.2022
  • Home
  • Privacy Policy
  • EPCI Membership & Advertisement
  • About
No Result
View All Result
NEWSLETTER
Passive Components Blog
  • Home
  • NewsFilter
    • All
    • Aerospace & Defence
    • Antenna
    • Applications
    • Automotive
    • Capacitors
    • Filters
    • Fuses
    • Inductors
    • Industrial
    • Integrated Passives
    • Market & Supply Chain
    • Medical
    • New Materials & Supply
    • New Technologies
    • Non-linear Passives
    • Oscillators
    • Passive Sensors
    • Resistors
    • RF & Microwave
    • Telecommunication

    Jianghai Launches Four New Stacked Polymer Capacitor Series

    High Voltage MLCC for EV Powertrain

    Capacitors Pre-charging in Drive Circuits Using Pulse-Withstanding Resistors

    Filter Q Factor Explained

    Würth Elektronik Introduces Snap-In Supercapacitors

    Skeleton to Build the World’s Largest Supercapacitor Factory

    Vishay Releases High Current, High Temperature Edge-Wound Inductors

    Murata Introduces Low DCR Power Over Coax Metal Alloy Chip Inductor

    Film Capacitor Failures Deep Dive Case Study

    Trending Tags

    • Ripple Current
    • RF
    • Leakage Current
    • Tantalum vs Ceramic
    • Snubber
    • Low ESR
    • Feedthrough
    • Derating
    • Dielectric Constant
    • New Products
    • Market Reports
  • VideoFilter
    • All
    • Antenna videos
    • Capacitor videos
    • Filter videos
    • Fuse videos
    • Inductor videos
    • Non-linear passives videos
    • Oscillator videos
    • Passive sensors videos
    • Resistor videos
    • Sensors

    Film Capacitor Failures Deep Dive Case Study

    Analogue Temperature Controller and Thermistor LTSpice Simulation Video

    Calculating the Inductance of a DC Biased Inductor

    Diode RC Snubber Explained

    Basics of PCB production, Part 1; WE Webinar

    Effects of Harsh Environmental Conditions on Film Capacitors

    Common-mode Choke Parameters Explained; WE Webinar

    Ceramic Capacitors Loss Modelling under High DC Bias Voltage and High Current Stress

    MLCC Case Size Impact to Parameters

    Trending Tags

    • Capacitors explained
    • Inductors explained
    • Resistors explained
    • Filters explained
    • Application Video Guidelines
    • EMC
    • New Products
    • Ripple Current
    • Simulation
    • Tantalum vs Ceramic
  • Knowledge Blog
  • Suppliers
    • Preferred Suppliers
    • Who is Who
  • Events
  • Home
  • NewsFilter
    • All
    • Aerospace & Defence
    • Antenna
    • Applications
    • Automotive
    • Capacitors
    • Filters
    • Fuses
    • Inductors
    • Industrial
    • Integrated Passives
    • Market & Supply Chain
    • Medical
    • New Materials & Supply
    • New Technologies
    • Non-linear Passives
    • Oscillators
    • Passive Sensors
    • Resistors
    • RF & Microwave
    • Telecommunication

    Jianghai Launches Four New Stacked Polymer Capacitor Series

    High Voltage MLCC for EV Powertrain

    Capacitors Pre-charging in Drive Circuits Using Pulse-Withstanding Resistors

    Filter Q Factor Explained

    Würth Elektronik Introduces Snap-In Supercapacitors

    Skeleton to Build the World’s Largest Supercapacitor Factory

    Vishay Releases High Current, High Temperature Edge-Wound Inductors

    Murata Introduces Low DCR Power Over Coax Metal Alloy Chip Inductor

    Film Capacitor Failures Deep Dive Case Study

    Trending Tags

    • Ripple Current
    • RF
    • Leakage Current
    • Tantalum vs Ceramic
    • Snubber
    • Low ESR
    • Feedthrough
    • Derating
    • Dielectric Constant
    • New Products
    • Market Reports
  • VideoFilter
    • All
    • Antenna videos
    • Capacitor videos
    • Filter videos
    • Fuse videos
    • Inductor videos
    • Non-linear passives videos
    • Oscillator videos
    • Passive sensors videos
    • Resistor videos
    • Sensors

    Film Capacitor Failures Deep Dive Case Study

    Analogue Temperature Controller and Thermistor LTSpice Simulation Video

    Calculating the Inductance of a DC Biased Inductor

    Diode RC Snubber Explained

    Basics of PCB production, Part 1; WE Webinar

    Effects of Harsh Environmental Conditions on Film Capacitors

    Common-mode Choke Parameters Explained; WE Webinar

    Ceramic Capacitors Loss Modelling under High DC Bias Voltage and High Current Stress

    MLCC Case Size Impact to Parameters

    Trending Tags

    • Capacitors explained
    • Inductors explained
    • Resistors explained
    • Filters explained
    • Application Video Guidelines
    • EMC
    • New Products
    • Ripple Current
    • Simulation
    • Tantalum vs Ceramic
  • Knowledge Blog
  • Suppliers
    • Preferred Suppliers
    • Who is Who
  • Events
No Result
View All Result
Passive Components Blog
No Result
View All Result

Capacitors Pre-charging in Drive Circuits Using Pulse-Withstanding Resistors

21.7.2022
Reading Time: 5 mins read
0 0
0
SHARES
4
VIEWS

This article published by Rutronik discusses pre-charging of capacitors using pulse-withstanding resistors in drive circuits.

Electric motors are usually controlled using converters. Electrolytic capacitors are frequently used to stabilize and buffer the DC voltage in the DC link.

RelatedPosts

Jianghai Launches Four New Stacked Polymer Capacitor Series

High Voltage MLCC for EV Powertrain

Filter Q Factor Explained

There are a number of issues to consider with switching these capacitors in and out of the circuit.

When a capacitor is charged through a resistor, the increase in voltage follows a curve in the form of a natural exponential function (Figure 1, blue line). The relevant charging current of the capacitor (green) on the other hand takes the form of a decaying natural exponential function.

Figure 1. The voltage and charging current of a capacitor follow opposing natural exponential functions.

In an example of charging of 5000uF 100V capacitor through 50Ohm resistor (see Fig.2.) the maximum current flows right at the start of the charging process, at which point it is 100 V/50 Ω = 2 A. After around 1.5 seconds the capacitor reaches a voltage of close to 100 V, while the current is close to 0 A.

Figure 2. Charging a capacitor at 5,000 µF to a voltage of 100 V through a resistor of 50 Ω.

Let’s say this capacitor is charged without using a resistor, so that when the voltage is “hard switched,” there is only a very low specific resistance in the supply line—estimated to be 10 mΩ—in which case there is theoretically a current of up to 10,000 A at the first moment of charging!

However, in reality, in addition to the ohmic resistance of the connecting wire, there are other elements providing resistance:

  • the ohmic resistance of the capacitor estimated at around 25 mΩ
  • the internal resistance of the voltage source estimated at around 20 mΩ
  • the transfer resistance of the connecting terminals, switching contacts, etc. of max. 5  mΩ

This means that a realistic total resistance would be around 50 mΩ. With this, there is a still a peak current of over 2,000 A (100 V/0.05 Ω = 2,000 A).

While this very high current would only be flowing for a very brief moment, you can still imagine what impact these current surges can have on other components — certainly so, when you remember that DC voltages of 800 V are commonplace in DC link solutions for converters nowadays.

Switch-On Processes in Consideration of Wire Inductance

If we consider not only the capacitance but also any wire inductance as shown in Figure 3, we observe behavior such as that seen in Figure 4.

Figure 3. Charging a capacitor at 5,000 µF to a voltage of 100 V with a resistance of 7 mΩ and a wire inductance of 7 µH.
Figure 3. Behavior of a capacitor during charging, taking wire inductance into account.

Without going into detail, the graph shows clearly that the voltage (blue curve) is no longer a natural exponential function, instead oscillating towards a value of around 100 V. Briefly, it will reach a value of up to 170 V, around 70% higher than the externally applied output voltage!

The current (green curve) also peaks at around 2,100 A just after switch-on due to the additional inductance.

In other words, the current reaches very high values and overvoltages with voltage surges of up to double the externally applied voltage possibly occurring even if all ohmic resistors, inductors, and capacitors to be charged in the charging circuit are accounted for.

This is why hard-switching a capacitor should always be avoided. Pre-charging a capacitor allows the aforementioned behavior to be almost entirely prevented.

Similar behavior occurs when discharging a capacitor, which is why it is also recommended to provide a resistor for the discharging process.

Pulse-Withstanding Pre-Charge Resistors

A very simple and cost-effective approach is provided here by pulse-withstanding charge resistors, which can be connected in series with the capacitor for a certain time. All that is needed here is a pre-charge branch connected in parallel to the main switch. This branch needs to fulfill the following requirements:

Use of the current-limiting effect of the resistor

Two-step switch-on process:            

  1. The pulse-withstanding resistor is used to pre-charge the capacitor until it has almost entirely reached the externally applied voltage level
  2. The capacitor is directly connected by bridging the pre-charge branch connected in parallel with the main switch

A mechanical or electrical lock-out mechanism that prevents switch-on without a pre-charge.

A wide range of pre-charge resistors is offered by leading power resistor manufacturers. These include cement-coated wire resistors from 3 to 18 W and high-load resistors with aluminum housing from tenths to hundreds W. Customized solutions can be often ordered as well for special requirements. For example, increased voltage requirements, special geometric forms, and also enhanced cooling solutions can be implemented.

Source: Rutronik

Related Posts

Capacitors

Jianghai Launches Four New Stacked Polymer Capacitor Series

21.7.2022
6
Automotive

High Voltage MLCC for EV Powertrain

21.7.2022
7
Capacitors

Würth Elektronik Introduces Snap-In Supercapacitors

20.7.2022
11

Popular Posts

  • Understanding High-Precision Resistor Temperature Coefficient of Resistance

    0 shares
    Share 0 Tweet 0
  • Ripple Current and its Effects on the Performance of Capacitors

    3 shares
    Share 3 Tweet 0
  • Why Low ESR Matters in Capacitor Design

    0 shares
    Share 0 Tweet 0
  • What is a Dielectric Constant of Plastic Materials ?

    4 shares
    Share 4 Tweet 0
  • Coefficient of Linear Thermal Expansion on Polymers Explained

    0 shares
    Share 0 Tweet 0
  • Leakage Current Characteristics of Capacitors

    0 shares
    Share 0 Tweet 0
  • How to Choose the Right Inductor for DC-DC Buck Applications

    0 shares
    Share 0 Tweet 0
  • Capacitor Selection for Coupling and Decoupling Applications

    28 shares
    Share 28 Tweet 0

Newsletter Subscription

 

Archive

2022
2021
2020
2019
2018
2017

  • Home
  • Privacy Policy
  • EPCI Membership & Advertisement
  • About

© EPCI - Premium Passive Components Educational and Information Site

No Result
View All Result
  • Home
  • News
  • Video
  • Knowledge Blog
  • Preferred Suppliers
  • Events

© EPCI - Premium Passive Components Educational and Information Site

Welcome Back!

Login to your account below

Forgotten Password?

Retrieve your password

Please enter your username or email address to reset your password.

Log In
This website uses cookies. By continuing to use this website you are giving consent to cookies being used. Visit our Privacy and Cookie Policy.