Snubber for flyback converter

Finally, figure 6c on the right shows the response with an RC snubber. The RC snubber dampens ringing, ensuring oscillations will not inadvertently turn the power switch back on. The LT has a minimum switch on time of ns so the ringing must not exceed this minimum limit. It is common to see either the Zener diode clamp or the RC snubber used in a flyback circuit; and it also is common to see both, as shown in figure 1 above.

A snubber circuit is generally recommended when using the high voltage LT to protect the switch node; however, there are special cases when a snubber circuit is not needed, resulting in an even more simplified schematic and a smaller solution footprint. It has robust switch protection and includes many circuits in the datasheet that do not include a snubber circuit as shown below in figure 8. This is well below the switch's V absolute maximum rating.

With the LT83xx family of monolithic, isolated flyback converters, designing a small, efficient, robust, isolated power supply is a fairly simple task.

The internal power switch, recommended off-the-shelf transformer and just a few external components all contribute to make the design process easy. A wide range of input voltage and output power combinations are available, which cover output power levels up to 24W.

In addition, LTspice files are readily available for circuit simulation, and demonstration circuits provide a convenient way to quickly exercise the solution.

He has been in the semiconductor industry for 26 years in applications, business management and marketing roles. He obtained a B. Optocoupler-Based Isolated Flyback Solutions The circuit below is a typical optocoupler-based isolated flyback solution. Part Number. Internal Power Switch. Input Voltage Range V.

Max Output Power W. Estimate the voltage in the capacitor with Equation 6 :. Note that if this equation is evaluated for t ON , it can be greatly simplified. Calculate the output voltage ripple with Equation 7 :. Next, choose a capacitor value to provide an optimal ripple voltage. The next design step involves the transformer. There are many design decisions involved in choosing a transformer, such as the core material and core shape. When choosing the core material and shape, each option has its own specific advantages.

For this example, the commonly used ferrite core in a double E shape was chosen see Figure 3. The method used to calculate the area of the transformer is called the A P method. Now the method and the design parameters have been defined, a quick set of calculations can be used to design the transformer. First, calculate the minimum transformer area using Equation 9 :. B MAX is typically a defined input parameter; for ferrite cores it is generally between 0.

Using the A P method, an EE13 core and a bobbin with a minimum 0. The maximum primary and secondary turns that can fit in the transformer are then calculated to maintain the turn ratio calculated in Equation 2.

Calculate the primary turn number with Equation 10 :. The last step of the design process is to find the snubber values.

Figure 5 shows a flyback converter with a snubber circuit. For the snubber, the design process is comprised of three stages. Then the values for the snubber components can be estimated. Calculate the maximum capacitor voltage with Equation 12 :. Estimate the power in the snubber resistor with Equation 13 :. Using the power as a limiting parameter, calculate the snubber resistor value with Equation 14 :.

Estimate the value of the snubbing capacitor with Equation 15 :. Lastly, calculate the maximum voltage across the snubber diode with Equation 16 :. Note that this circuit includes the components that have been previously mentioned, such as the primary inductor L P , the auxiliary inductor L P2 , the output capacitor which is made up of the parallel addition of C 2A , C 2B , and C 2C for improved frequency response , the rectifier diode D 1 , and the snubber circuit. The controller includes the MOSFET switch and all of its related circuitry, as well as some additional components for noise filtering.

This article used the MP from MPS to demonstrate how to design a flyback converter in eight simple steps. Though there are many more things to consider before a design is ready for implementation — such as passing EMC tests, control loop design, and component selection — it is important to establish a clear method for calculating and selecting components. Many design decisions will have significant effects on the overall behavior of the system, so establishing the input design parameters is a crucial first step.

These parameters set the constraints for the converter design, and the remaining steps involve selecting values in accordance with these specifications. Typical values of pF are often seen in commercial adapters and they also offer some snubbing advantage too. Your snubber is wrong - you simply can't use a regular diode to "snub" all the reflected voltage onto a uF capacitor from the secondary because that means you get very little secondary voltage at all.

The voltage produced by the secondary "reflects" to the primary and, when the MOSFET switching device turns off to release energy to the secondary, the secondary voltage raises the MOSFET drain, in many cases to more that twice the incoming DC voltage: -. You can use simple RCD snubbers without a zener but not with a value of capacitance of uF because it will accumulate all the energy and never get discharged by the parallel resistor between cycles. The idea about a snubber is that it extracts as little possible energy from what gets transferred and converts what can't get transferred to heat in the parallel resistor.

Your CR time 2k2 and uF is 1. If you are aiming to get a 3. This might mean a peak positive secondary voltage of 3. So, it boils down to how much energy is released by the primary leakage inductance - you have told us "k" but you haven't told us the value of the primary inductance or how much power is being transferred so it ends here almost If, the transformer were actually a step up type of the flyback management would be easier because the reflected voltage to the primary MOSFET instead of being 3.

However, it would be an inefficient design using a step up transformer to produce a secondary voltage so low. Your pictures show an output DC voltage of 5 volts and this will have to mean that the output secondary winding has more turns than the primary winding - unorthodox but doable but not with uF.

Note that the output voltage remains at 5 volts but the peak drain voltage is just about falling below 17 volts. Maybe this is what needs to be done? Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?

Learn more. Design R C snubber for flyback converter Ask Question. Asked 1 year, 7 months ago. Active 1 year, 7 months ago.