The RCD clamp does contain a diode that gets forward biased when the spike gets too high. Note that dissipating also impacts efficiency so the goal is to dissipate only as much as necessary to protect the switch.
Thats a good question. We will check if we can find an answer. You could also measure the voltage on the switch directly since N is just used to calculate it from the reflected secondary.
@@OMICRONLabTutorials last night I was using your method on my 12V-300V boost converter and I got great results on damping the ringing on the mosfet and reduced voltage to a very safe limit. Super happy. Next I'll test across the diode. Will this same trick work with an SCR? FYI I'm building a motorcycle capacitive discharge ignition system. Thanks for sharing your huge knowledge!
@@TYGAMatt thanks for your feedback, we will forward it to the presenter Dr. Ali Shirsavar. For detailed technical questions, please use support@omicron-lab.com. Thanks!
There is an error in APS_8. The formula says Vc_snub=Vin + N*Vout, but the calculations say Vc_snub=(Vin/N)+Vout. Which one of the two is right? As the turns ratio is 1:1, you did not notice the error cause the result was the same...
Dear David, thanks a lot for your message! We talked to Dr. Ali and he mentioned that the formula is for a primary snubber, so the secondary voltage is referred to primary. Next time he will also show the formula how to refer the primary voltage to secondary for completeness. We hope that helps!
Sorry to bother you again. My transformer is pri: 9T and sec:150T so a ratio of 0.06. I measured a primary leakage of 162nH by shorting the secondary and measuring with my LCR meter. For the diode snubber I need to refer this leakage to the secondary. Am I correct that it is 162nH / 0.06^2 = 45uH? I can then calculate the resistor as: 2*Pi*Fr*0.000045 = resistor value
If your snubber and switch are on the primary, then there is no need to refer the measured leakage to secondary. For further discussion, please send a message to support@omicron-lab.com.
@@OMICRONLabTutorials I have an RC snubber across the mosfet on the primary side. It works very well. Now I want to put a snubber on the diode but not exactly sure the leakage value to use for the resistor value.
A quick question if I may. What type of capacitor should one use in the snubber? I've been using a polyester cap. Is it possible to use a ceramic smd cap as this would be useful for saving some real estate on the PCB. Thanks. Matt
For Vout, is this your desired output voltage or the voltage determined by the turns ratio? I'm confused with this because I am charging a capacitor to 1kV over time, but using a 1:8 step-up transformer with a 28V supply voltage. To me, this value should be the 1kV. Thanks for your time.
Maybe a better way to consider this is that even with a blocking diode and charging a capacitor, since little to no current will be flowing through the diode, the secondary of the transformer is close to the node voltage of the capacitor. In this thought, I believe I would design around the higher voltage (1kV) as I want the diode of the RCD to turn on sooner rather than later when considering the additional voltage seen on the primary as reflected from the secondary.
Dear mpachol88, thanks a lot for your inquiry! Please be aware that Vout is the output voltage. If you have any further questions, please feel free to contact Dr. Ali Shirsavar via his website: www.biricha.com/contact-us.html best regards, your OMICRON Lab team
Dear Biricha. I dont understand a little part. You do a calculation of value of R by to get a Q=1, considering the capacitor value of the mosfet capacitor but you later said that you have to choose value of Csnubber to get a Q=1. It wasnt enough the calculation of R with the capacitance of transistor to get a Q=1 ?
Sometimes it might be enough to place a damping resistor but here Csnub is required otherwise the R would bypass the transistor. Unfortunately, the extra Csnub will also impact how the damping works. So there are to extra elements that need to be selected / calculated. R & Csnub
Thanks Biricha for your answer. I have another question. Why is not enough take a value of capacitance Csnubber of equal or greater than parasitic capacitance of mosfet to get a Q=1 ?
@@bolivarcoello236 not sure if I understand that correctly. You might want to post your questions at support@omicron-lab.com. Adding a capacitor only will not really add damping. You need a resistor to add damping. The snubber capacitor is preventing the switching frequency to pass thru the damping resistor but it lets the high ringing frequency thru so that the damping can be active at the high ringing frequency. It is basically a high-pass filter for the damping.
Thank you for sharing the excellent snubber design tips....Thank you for keeping it very simple and easy to understand...
Thanks sir for sharing the informative and valuable video . Very well and simply explained the concept it is is very useful for us
Dumb question. Why just not to put a single diode across inductor so the power just dissipated in it? Every single amateur scheme have it😅
The RCD clamp does contain a diode that gets forward biased when the spike gets too high. Note that dissipating also impacts efficiency so the goal is to dissipate only as much as necessary to protect the switch.
@@OMICRONLabTutorials thanks, i'm learning, your lectures are very helpful
Thanks for explanation
Hi sir,how to select the primary diode rating for RCD Snubber design..
Please contact Biricha directly for this question.
best snubber explanation! thanks. What if the flyback has multiple isolated output? what would be the N?
Thats a good question. We will check if we can find an answer. You could also measure the voltage on the switch directly since N is just used to calculate it from the reflected secondary.
Incredibly informative. Excellent teaching style.
Glad you think so!
@@OMICRONLabTutorials last night I was using your method on my 12V-300V boost converter and I got great results on damping the ringing on the mosfet and reduced voltage to a very safe limit. Super happy. Next I'll test across the diode.
Will this same trick work with an SCR?
FYI I'm building a motorcycle capacitive discharge ignition system.
Thanks for sharing your huge knowledge!
@@TYGAMatt thanks for your feedback, we will forward it to the presenter Dr. Ali Shirsavar. For detailed technical questions, please use support@omicron-lab.com. Thanks!
@@OMICRONLabTutorials many thanks for your reply. I am sure that you guys are super busy so I really appreciate it.
There is an error in APS_8. The formula says Vc_snub=Vin + N*Vout, but the calculations say Vc_snub=(Vin/N)+Vout. Which one of the two is right? As the turns ratio is 1:1, you did not notice the error cause the result was the same...
Dear David, thanks a lot for your message! We talked to Dr. Ali and he mentioned that the formula is for a primary snubber, so the secondary voltage is referred to primary. Next time he will also show the formula how to refer the primary voltage to secondary for completeness. We hope that helps!
Hi sir, would you clarify me that how you have considered the value 2.5 to 5 in C clamp calculation,is any reference for that ???
In the video, the reference points to Basso's book: Switch-Mode Power Supplies Spice Simulations and Practical Designs". Please check there. Thanks!
@@OMICRONLabTutorials Thank you so much sir..
Sorry to bother you again.
My transformer is pri: 9T and sec:150T so a ratio of 0.06.
I measured a primary leakage of 162nH by shorting the secondary and measuring with my LCR meter.
For the diode snubber I need to refer this leakage to the secondary. Am I correct that it is 162nH / 0.06^2 = 45uH?
I can then calculate the resistor as:
2*Pi*Fr*0.000045 = resistor value
If your snubber and switch are on the primary, then there is no need to refer the measured leakage to secondary. For further discussion, please send a message to support@omicron-lab.com.
@@OMICRONLabTutorials I have an RC snubber across the mosfet on the primary side. It works very well.
Now I want to put a snubber on the diode but not exactly sure the leakage value to use for the resistor value.
Could you tell me where I can find the spreadsheets please? Thanks.
Please have look here: www.biricha.com/snubber.html
A quick question if I may. What type of capacitor should one use in the snubber? I've been using a polyester cap.
Is it possible to use a ceramic smd cap as this would be useful for saving some real estate on the PCB.
Thanks.
Matt
Ceramic should be well suited since it normally has high ripple current capabilities.
@@OMICRONLabTutorials Thank you very much for your reply. Very helpful
For Vout, is this your desired output voltage or the voltage determined by the turns ratio? I'm confused with this because I am charging a capacitor to 1kV over time, but using a 1:8 step-up transformer with a 28V supply voltage. To me, this value should be the 1kV. Thanks for your time.
Maybe a better way to consider this is that even with a blocking diode and charging a capacitor, since little to no current will be flowing through the diode, the secondary of the transformer is close to the node voltage of the capacitor. In this thought, I believe I would design around the higher voltage (1kV) as I want the diode of the RCD to turn on sooner rather than later when considering the additional voltage seen on the primary as reflected from the secondary.
Dear mpachol88,
thanks a lot for your inquiry!
Please be aware that Vout is the output voltage.
If you have any further questions, please feel free to contact Dr. Ali Shirsavar via his website: www.biricha.com/contact-us.html
best regards,
your OMICRON Lab team
Dear Biricha. I dont understand a little part. You do a calculation of value of R by to get a Q=1, considering the capacitor value of the mosfet capacitor but you later said that you have to choose value of Csnubber to get a Q=1. It wasnt enough the calculation of R with the capacitance of transistor to get a Q=1 ?
Sometimes it might be enough to place a damping resistor but here Csnub is required otherwise the R would bypass the transistor. Unfortunately, the extra Csnub will also impact how the damping works. So there are to extra elements that need to be selected / calculated. R & Csnub
Thanks Biricha for your answer. I have another question. Why is not enough take a value of capacitance Csnubber of equal or greater than parasitic capacitance of mosfet to get a Q=1 ?
@@bolivarcoello236 not sure if I understand that correctly. You might want to post your questions at support@omicron-lab.com.
Adding a capacitor only will not really add damping. You need a resistor to add damping. The snubber capacitor is preventing the switching frequency to pass thru the damping resistor but it lets the high ringing frequency thru so that the damping can be active at the high ringing frequency. It is basically a high-pass filter for the damping.