• Get Listed
    • Get a FREE Quote for your Next Project
HardwareBee
  • Find ASIC Vendors
  • Browse Design Services Directory
    • FPGA Design Services
    • Electronic Design Services
    • Embedded Software Companies
    • Add a Vendor
  • Get 3 Quotes From
    • FPGA Design Companies
    • FPGA IP Core Vendors
    • Electronic Design Companies
    • Embedded Software Companies
    • Design & Manufacturing Vendors
  • WikiBee
  • Resources
    • FPGA Academy
    • Embedded Academy
    • FPGA vs ASIC Calculator
  • Calculators
    • Watt to dBm Converter
    • dBm to Watt Converter
  • Emerging ICs
    • SPARK Microsystems – SR1000
    • Cologne Chip – GateMate
  • Pricing
    • Get Your Company Listed
    • Get Monthly Outbound Leads
    • Get Free Consulting
HardwareBee
  • Browse Design Services Directory
    • FPGA Design Services
    • Electronic Design Services
    • Embedded Software Companies
    • Add a Vendor
  • Get 3 Quotes From
    • FPGA Design Companies
    • FPGA IP Core Vendors
    • Electronic Design Companies
    • Embedded Software Companies
    • Design & Manufacturing Vendors
  • WikiBee
  • Resources
    • FPGA Academy
    • Embedded Academy
    • FPGA vs ASIC Calculator
  • Calculators
    • Watt to dBm Converter
    • dBm to Watt Converter
  • Emerging ICs
    • SPARK Microsystems – SR1000
    • Cologne Chip – GateMate
  • Pricing
    • Get Your Company Listed
    • Get Monthly Outbound Leads
    • Get Free Consulting
3168 Views

Understanding DV/DT in Electronics

14/11/2022, hardwarebee

High-speed switching circuits, like SCR, MOSFETs, and BJTs, are sensitive to the rate of change (rise) of the voltage applied to the device. In switching circuits, dV/dt represents the instantaneous rate of change of voltage with respect to time (volts per second increase or decrease).

 

The dV/dt rating of any semiconductor device is an important parameter since it demonstrates the maximum rate of rise of applied voltage that does not bring the device into conduction or false turn-on. It must be less than the specified dV/dt limit of the device.

 

Turn-off snubber circuits are employed to overcome this problem. They help to prevent the sudden rise of dV/dt across the device. These circuits are not only used in the suppression of high-voltage transients but also offer many benefits:

 

  1. Reduce switching losses and transfer them to an external resistor.
  2. Reduce noise and EMI
  3. Prevent the second breakdown in BJT switches

 

DV/DT in BJT

 

In BJT switching circuits, it is the rate of rise of the collector to emitter voltage.

In these switching circuits, there are some delays associated with switching speed like delay time and storage time. Ignoring these two delays, BJT switching waveforms are like this.

 

Figure 1:  BJT switching waveforms

 

During turn-off time, dV/dt should be within limits. For a power BJT collector current, IC falls, and VCE should not rise immediately. Otherwise, a second breakdown may occur. To control the rate of rise of VCE, a simple RC snubber circuit is connected in parallel with BJT or in between collector and emitter junctions. It limits the rate of a sudden rise in VCE during turn-off time.

 

Figure 2: A BJT transistor with dV/dt protection

 

Have a look at the circuit diagram. DS, CS, and RS constitute a snubber circuit. During turn-off time, the equivalent circuit is given below.

 

Figure 3: Equivalent circuit during turn-off time

 

As the BJT turns off, the DS turns on.

 

The capacitor CS is charged by the load current IL (assume IL is freewheeling through diode Df). The load current flows through the capacitor and charges it linearly up to VS. Once the capacitor is charged, the resistor RS is there to provide the discharging path.

 

 

The above equation shows the dV/dt across the transistor during off time. By choosing suitable values of CS and RS, it is possible to limit the dV/dt across the transistor.

 

DV/DT in MOSFETS

 

In MOSFETs, it is used to specify the switching transient period. In other words, it is the rate of change of voltage Vds (drain-source voltage) caused by switching influence. Power MOSFETs are designed for switching purposes. When it operates in a linear region, it has large transconductance, parasitic capacitance, and stray inductances (between gate and source and other interconnections) that probably form a positive feedback path and stimulate undesirable or parasitic oscillations. This happens particularly during transient switching periods because of higher transconductance values. Interaction of high dV/dt with the circuit parasitic inductances and capacitances will result in overshoot and oscillations during the turn-off time.  Due to these oscillations, the transistor is off and on repeatedly. It will result in high power dissipation, which may lead to burnout.

 

 

Figure 4: Ringing and overshoot

 

Two key ways can cause this dV/dt-induced failure.

 

The first effect is associated with parasitic BJT.  If the applied voltage rises suddenly, it might turn on the MOSFET unintentionally when it is supposed to be off. There is a high voltage at the drain terminal, which may cause damage as well.

 

Let’s take a deep dive into this mechanism.

 

Figure 5: The parasitic BJT

 

  1. Consider the MOSFET in the off-state.
  2. Look at the capacitance CBD which is connected between the base of the NPN and the drain of the MOSFET. A rapid increase in voltage between the source and drain will generate a current I2.
  3. I2 will flow from RB. If the voltage drop across RB becomes greater than VBE then it will turn on parasitic BJT. It will drive the MOSFET into an avalanche, a destructive condition.

 

The dV/dt capability of this mechanism is given by:

 

 

There are several ways to avoid dV/dt:

  1. Reduce RB. It is a device parameter and a circuit designer can not control it.
  2. VBE and RB are temperature-dependent.
  3. It is better to control the switching speed of a MOSFET.

 

 

The second effect is active through the feedback action of internal capacitance between the gate and drain CGD.

 

Figure 6: The feedback path because internal gate and drain capacitance

 

  1. Assume the transistor is off.
  2. Apply ramp voltage across the drain and source terminal. A sudden increase in the voltage Vds will result in current I1 due to CGD
  3. I1 will flow from RG. RG is the gate resistance and II is the current flowing through it. Then voltage across the gate terminal is given by:

 

 

  1. If VGS becomes greater than the threshold voltage of the MOSFET (Vth), it will start conduction unintentionally. The dV/dt capability for this mechanism is given by:

 

 

There are several ways to avoid this condition:

  1. It is clear from the equation that low Vth devices are more likely to suffer from dV/DT.
  2. Vth is temperature-dependent.
  3. The Gate circuit is an important parameter, it is a device parameter. Higher gate oxide thickness reduces CGD and increases Vth. From the dV/dt relationship, decreased CGD will increase dV/dt capability.

 

DV/DT in Thyristors

 

In thyristors, dV/dt is the rate of change of applied anode to cathode voltage (VAK). It is also known as the rate of rise of OFF-state voltage. If dV/dt increases beyond the specific value stated in the datasheet, then it may cause a false triggering of SCR. The false triggering is caused by the internal junction capacitive current in the gate area.  Let’s suppose the internal junction capacitance of the device is C. When the rate of rise of voltage across the anode to cathode (dVAK/dt) is very high, a displacement current ‘i’ is generated because of the internal capacitance. Even in the absence of external current flowing through the gate terminal, this current is sufficient to activate the thyristor. The system will unintentionally enter forward conduction mode as a result.

 

To avoid this condition, snubber circuits are used. The foremost objective is to prevent spurious turn-on of a thyristor due to the high rate of rise of the applied voltage (VAK). It is a series RC network. It is connected in parallel with the thyristor.

 

Let’s connect a single capacitor of a suitable value that is connected in parallel with a thyristor.  When switch S1 is closed at t = 0, the voltage(VAK) is applied across the thyristor T. The dV/dt may be sufficient to turn on the device. The capacitor CS limits the rate of rise of applied voltage. The discharge current of the capacitor is limited by adding a resistor RS in series.

Figure 7: A snubber circuit without a discharging resistor.

 

Figure 8: Illustration of a snubber circuit with a discharging resistor.

 

The voltage across the thyristor rises exponentially. It is limited by choosing suitable values of capacitor and resistor. The dV/dt can be determined with the help of the following formula:

 

 

linked in icon
Sign up for HardwareBee
* = required field

Recent Stories

5+ Best UWB Chipset Providers Compared
5+ Best UWB Chipset Providers Compared
SPARK Microsystems Announces CDN$48 Million Financing Led by Idealist Capital
SPARK Microsystems Announces CDN$48 Million Financing Led by Idealist Capital
What is MicroLED? Overview, Benefits and Future
What is MicroLED? Overview, Benefits and Future
Auto processor market growing at 13% CAGR 22-28
Auto processor market growing at 13% CAGR 22-28
The Ultimate Guide: Current Mirror
The Ultimate Guide: Current Mirror
What is the Difference: GDDR5 VS. GDDR6
What is the Difference: GDDR5 VS. GDDR6
Watt to dBm (free) Converter
Watt to dBm (free) Converter
dBm to Watt (free) Converter
dBm to Watt (free) Converter
Get 3 Quotes from Electronic Design Companies
Get 3 Quotes from FPGA Design Companies
Get 3 Quotes from Embedded SW Services
Get 3 Quotes from EMS Companies

Find Design Services

Get Price Offers From
  • Electronic Design Services
  • FPGA Design Services
  • Embedded Software Companies
  • PCB Layout Services
  • Printed Circuit Board Manufacturers
  • Design & Manufacturing Services
Welcome New Vendors
  • Cologne Chip – GateMate
  • SPARK Microsystems – SR1000
  • TrigoPi
  • Fidus Systems
  • PCB Design
Answer a Question
  • Tips For Installing a PCB Prototype Board
  • Benefits of Working With a Reliable Flex Printed Circuit Board Manufacturer
  • FPGA company gross margin?
  • What is an FPGA used for?
  • When was FPGA invented
Recent WikiBee Items
  • Buck Boost Converter
  • Intel Quartus Prime
  • Transimpedance Amplifier
  • VHDL
  • Hardware vs. Software
Recent Posts
  • 5+ Best UWB Chipset Providers Compared
  • SPARK Microsystems Announces CDN$48 Million Financing Led by Idealist Capital
  • What is MicroLED? Overview, Benefits and Future
  • Auto processor market growing at 13% CAGR 22-28
  • The Ultimate Guide: Current Mirror
Most Popular Blog Posts
  • Promwad Accelerates Product Development with Vendor-Agnostic FPGA Design in Multiple Industries 
  • Understanding Knee Voltage
  • Understanding UPS Block Diagram
  • Understanding DV/DT in Electronics
  • Understanding Charge Pump

Never miss an update!

Follow us on LinkedIn

Do you need any price
information?

(Electronic design, FPGA design, Embedded SW services, PCB design, Turnkey)

Yes
No
HardwareBee

Copyright 2017-2023, HardwareBee. All rights reserved.

  • About Us
  • Contact
  • Subscribe
  • News
  • Get Free Support
  • Get listed
  • Send a wiki/article
  • Advertise

Follow Us

Be sure to follow our LinkedIn company page where we share our latest updates LinkedIn
Partner with us Partner with us

Design and Manufacturing Services

  • Engineering Design Services
  • Electronic Design and Manufacturing
  • Electronic Product Development
  • Electronic Product Design
  • Electronic Consulting Services
  • Electronic Engineering Companies
  • Electronic Engineering Services
  • Electronic Product Design and Development
  • Electronics Design Services
  • Electronics Design Company
  • Electronic Design Consultants
  • Electronic Design Company
  • FPGA Design Company
  • FPGA Consultant
  • FPGA Design Services UK
  • Electronics Manufacturing services
  • Electronics Manufacturing Companies
  • Electronic Contract Manufacturing Companies
  • Electronic Manufacturing Services Companies
  • EMS Companies Directory
  • Electronic Design Services
  • FPGA Design Services
  • Embedded Software Companies
  • PCB Layout Services
  • Printed Circuit Board Manufacturers
  • Design and Manufacturing Services