Snubber Circuit Design

Mosfet RCD Snubber Circuit Design

Design the MOSFET RCD snubber circuit

Push-Pull Snubber Circuit

Mosfet Snubber Circuit in Flyback Converter Circuit

Switch Protection Design - Fast-Recovery Diodes

Switch Protection Design - Fast-Recovery Diodes

Abstract
The number of fast recovery applications in high power systems
continues to grow leading to various dynamic constraints and
hence different diode designs and behaviours. Along with
conventional RC (“SCR-type”) and C (“GTO-type”) snubber
conditions, snubberless conditions in both IGBT and IGCT
applications are gaining ground at ever higher currents and
voltages (presently 6 kV). Within these two groups, the further
distinctions of “inductive” and “resistive” commutation di/dt must
be made for an optimal diode design. Diodes capable of high
reverse di/dt and dv/dt can today be realised thanks to controlled
life-time profiling which will be described here with both measured
and simulated results. As will also be explained, such “robust”
designs, though essential for snubberless operation, may be “less
robust” under snubbered conditions so that a clear understanding
of the application (Snubber, Free-Wheel, Clamp, Resistive or
Inductive di/dt) is required for the correct choice or design of a fast
recovery diode. The different diode commutation conditions will
be described and categorised and the optimal diode design
identified with supporting measurements and simulations.

Fig 2 “Inductive” commutation circuit fitted
with snubber and clamp

Traditionally the diode under consideration (in this case a
Free-Wheel Diode (FWD)) is fitted with a snubber and may also
be fitted with a clamp as shown in Fig. 2. Thus for the inductive
commutation circuit, we can define the additional sub-conditions
consisting of permutations of the snubbered/unsnubbered &
clamped/unclamped conditions whereby the snubber controls
the Duet’s dv/dt whereas the clamp controls its peak voltage.

More pdf

Mosfet Snubber Circuit in Flyback Converter Circuit

Mosfet Protection in flyback Circuit

PKC-136

PEAK CLAMP

CHARACTERISTICS
VBR 160Vdc
VDRM 700Vdc
P 1.5W

Feature
- Protection of the Mosfet in flyback power supply
- TRANSIL™ and blocking diode in a single
package

BENEFITS

- Accurate voltage clamping regardless load
- Reduced current loop
- Reduced EMI emission
- High integration
- Fast assembly
- Reduced losses in stand by mode

PKC-136 datasheet pdf


Mosfet Snubber Circuit in Flyback Converter

Fig. 1 Typical flyback convertor with drain clamping circuits

ZenBlock
Zener with integrated blocking diode
Philips Semiconductors' new ZenBlockTM replaces
double-diode-, RCD- or RC-snubbers in flyback convertors.
The new components offer circuit designers the important
benefits of lower component count and board usage, reduced
EMI, optimal clamping at all loads and higher efficiency.

Introducing

The new ZenBlock combines the double diode snubber in one
package. This leads to the following advantages:
-Fewer components.
-Reduced circuit board space
-Lower EMI by reducing the drain clamp circuit length and
area.
-Optimal clamp performance at all loads (compared with RCD
and RC snubber)
-Higher efficiency at low loads (compared with RCD and RC
snubber)

ZenBlock datasheet pdf

Push-Pull Snubber Circuit

Abstract
The DS3984, DS3988, DS3881, DS3882, DS3992, and DS3994
are cold-cathode fluorescent lamp (CCFL) controllers that use a
push-pull architecture to create the high-voltage AC waveforms
needed to drive the lamps. In a push-pull drive scheme, the
parasitic inductance of the step-up transformer, together with the
parasitic capacitance of the output of the n-channel power
MOSFETs, form a resonant circuit that can create unwanted
voltage spikes. High-voltage spikes can increase the stress on
the power MOSFETs and can also increase the electromagnetic
interference (EMI) created by the system. This application note
describes how to suppress the voltage spikes with a simple
resistor-capacitor (RC) network.

Push-pull drain snubber circuit.

more pdf

Mosfet RCD Snubber Circuit Design

Design Guidelines for RCD Snubber of Flyback Converters
Application Note AN-4147
Fairchild Semiconductor
Snubber design
The excessive voltage due to resonance between Llk1 and
COSS should be suppressed to an acceptable level by
an additional circuit to protect the main switch.

The RCD snubber
circuit and key waveforms are shown in Figures 2 and 3.
The RCD snubber circuit absorbs the current in the leakage
inductor by turning on the snubber diode (Dsn) when Vds
exceeds Vin+nVo. It is assumed that the snubber capacitance
is large enough that its voltage does not change during one
switching period.

When the MOSFET turns off and Vds is charged to Vin+nVo,
the primary current flows to Csn through the snubber diode
(Dsn). The secondary diode turns on at the same time.
Therefore, the voltage across Llk1 is Vsn-nVo. The slope of
isn is as follows:
more(pdf)

Snubber Circuits Suppress Voltage Transient Spikes in
Multiple Output DC-DC Flyback Converter Power Supplies
RCD Voltage Snubber
This snubber is applicable to rate-of-rise voltage control
and/or clamping. The presence of the diode in the
configuration makes this a polarized snubber. The two
possible configurations for this resistor-capacitor-diode
(RCD) snubber are shown in Figure 2. The configuration
shown in Figure 2A can only act as a voltage clamp.
The variation shown in Figure 2B is applicable to either
rate-of-rise control or clamping of the drain voltage of
the switch.

RCD Clamp
In the clamp mode the purpose of the snubber is to
clamp the voltage during turn-off at the drain of the
MOSFET. The parallel RC circuit may be returned to
ground or to a voltage other than ground (i.e., input voltage
if the drain can go above input voltage) since this will
reduce the power dissipation in the resistor. The MOSFET
switch itself will have to sustain the peak power dissipation
during turn-off. The value of the capacitor, CCLAMP,
and resistor, RCLAMP, is based on the energy stored in
the parasitic inductance, as this energy must be
discharged into the RC network during each cycle.
The voltage across the capacitor and resistor sets the
Clamp voltage, VCLAMP.

Rate-of-Rise Control RCD Snubber
When the RCD snubber is used to control the rate of
voltage rise at the MOSFET drain, the capacitor must be
completely charged and discharged during each cycle to
be able to control the rate-of-rise of the drain voltage.
The RC time constant of the snubber should, therefore,
be much smaller than the switching period (consider the
effect of duty cycle on pulse width). Typically, the time
constant should be about 1/10th the switching period.
When the switch turns off, the inductor current is diverted
through the snubber diode to charge the capacitor to
the rail. At that time, it is expected that the output rectifier
will turn on.

more(pdf)

MAGNETIC SNUBBER FOR 200W PFC
WITH UNIVERSAL MAINS
In high voltage continuous mode boost converters,
a significant part of the power mosfet switching
losses is related to the turn-on edge.
In fact, at turn on, the power mosfet has to sustain
both the boost diode reverse recovery and
the stray capacitances associated energies.
Moreover, the additional peak current due to the
recovery of the diode can be significantly high, in
particular at high temperature, thus increasing the
high frequency noise, the E.M.I. filter requirements
and reducing efficiency.
The turn on peak current, generating all the
above mentioned problems, has been dramatically
reduced by using the magnetic snubber we
propose at Fig. 1b.
The concept of this snubber is to reduce (and
control) the turn-on di/dt of the mosfet to the most
convenient value, considering the voltages and
switching frequency applied to the system.

Voltage Snubber

Magnetic snubber

more(pdf)

Design the MOSFET RCD snubber circuit