@Born2BeWiredIt would be interesting to take a scope reading by running a twisted pair of wires from the output to the scope. One end of the twisted pair soldered to one of the output capacitors and the scope probe and ground connects on the far end.
I don't think it's the main inductor that is at fault here. The pulse is too fast (@100Mhz) for the 100uH sized coil. It is probably in the freewheeling diode and the lead inductance and the IC lead inductances. Remember the diode has to suddenly conduct 1-3Amps of current and while conducting current suddenly a reverse voltage is applied to it. You can see those pulses in a circuit simulator. For example the diode reverse recovery alone manifests as a huge pulse of current through the diode.
buck regulator ba to sir born?anu po yung switching frequency nyang ginawa mo po?
Born, can you publish the schematics here? I do not have much experience with SMPS but in my view radiated switching noise from the inductor is just the effect. It will not be that big if it is small at the source. The real cause is the device that is switching on and off, the circuit around it and the layout. In my short stint with a company that makes SMPS, meeting output noise specs and EMI specs was a real challenge. A lot of circuit modifications have to be made after the first few boards are made and tested to reduce output noise and EMI. One thing nice about switching spikes is that the source can usually be easily identified. Once identified, you can apply the appropriate method of suppression or you can search for a new method.
It would be interesting to take a scope reading by running a twisted pair of wires from the output to the scope. One end of the twisted pair soldered to one of the output capacitors and the scope probe and ground connects on the far end.
If my pldt dsl connection be kind enough to give me an internet access. (My pldt dsl do not work during peak hours. Parang yung dating mwss, you have to wait till the wee hours to get the service.)
Inductor usually contribute some "noise" magnetic field generator and hence, it is a good practice to shield the inductor.. take note also the brand of inductor.. the higher the current rating, the lower the noise generated ..I think the "ringing spikes" that occurs in the circuit .. i will coin the term "frequency noise at low-level" for clarity.. has something to do with the "magnetostriction" , "gibbs phenomenon" and "air gaps".. There are some IC's (or regulators specifically) available that emits "Low-EMI" noiseIn communication systems, noise voltage can be calculated and should be in the micro-volts level under normal circumstances..Therefore, if the noise voltage under SMPS is "under the micro-volts umbrella" then the noise level is acceptable ..
Bro baka maktulong din to. Kasi minsan ang twisted pair is not good enough. Please make sure the wires are as short as possible. We used this method in my old job.
pero sa tigin ko po mas ok po pag X1 lang po ng probe at AC coupled at 20Mhz BW is farily enough tapos lagyan din ng kahit low esr na cap across output(typical 0.1uF na ceramic ay ok but mas ok pag 1uF na tantalum type) pag nagmemeasure ng output ripple.saka masyadong atang malaki yung toroid kasi base dun sa mataas na switching frequency kailangang maliit lang yung toroid inductor kasi yun yung purpose ng high switching freq to maximize the power density at dapat maliit din yung area ng loop traces ng PCB kumbaga madami ng parasitics considerations pag masyadong malaki yung loop ng PCB traces.maingay po talaga smps nakikita lalo ng approaching MHz sa switching freq kaya minsan ginagawa nilang ishield yung switching devices using heatsink pero sa nakikita ko naman dun sa board na isa ok naman layout nya pero malaki ripple parin kulang pa ng cap sa output.liliit po yung ripple using low esr output caps,small loop area for pcb layout traces at syempre compensation para kahit anong noise na papasok,stable parin yung output but pag high freq switching freq better to use resonant type kasi pag PWM lang na hard switching malaki switching losses but disadvantages naman ng resonant,efficient lang po pag malapit na magfull load.
sample ng ripple measurement 5V @ 10A na nasukat ko po,yung set-up gaya po kay sir TinTopHack,wala na akong nilagay na cap across,16mVpp ang result.
with a toroid core shielding is not an issue, as feared by e.novacek, I feel..