you have to measer the DC current in which means you need to install a L-C filter.... a small inductor and a HUGE capacitor at the input pin of the buck converter. You have to get the input current to DC so the meter will read it correctly. Then calculate input power (volts times current). Measure output voltage and current, calculate power. Eff is ratio of output power to input power.I am going to build a 12 - 5V step down buck regulator based on the MC34063. Once I am done. Assuming I get it working. I would like ti measure it's efficiency. How would O go about doing that?
A non true-RMS meter (the usual inexpensive multimeter) will measure the average of any ripple current plus the DC component of the input current which is what you want. So all you should need is a capacitor on the input to provide acceptable accuracy. The input capacitor that is normally part of a proper design should be adequate.you have to measer the DC current in which means you need to install a L-C filter.... a small inductor and a HUGE capacitor at the input pin of the buck converter. You have to get the input current to DC so the meter will read it correctly. Then calculate input power (volts times current). Measure output voltage and current, calculate power. Eff is ratio of output power to input power.
Not usually true. Switchers these days are cranking above 100 kHz, some above 1 MHz. TRMS meters don't measure accurately that high.A non true-RMS meter (the usual inexpensive multimeter) will measure the average of any ripple current plus the DC component of the input current which is what you want. So all you should need is a capacitor on the input to provide acceptable accuracy. The input capacitor that is normally part of a proper design should be adequate.
Again, not usually true. Most app circuits recommended by the manufacturer spec the absolute min size cap for functionality, they don't care how much current ripple is going back up the line. The reason is marketing always insists that the "recommended design" component cost be as cheap as possible.The input capacitor that is normally part of a proper design should be adequate.
Make an L-C filter. You can wrap maybe 20 turns of wire around a pencil to make an inductor. Put a big cap near the input of the device. Insert the ammeter on the power source side of the inductor.OK so what do I need to do here? There seems to be difference of opinion.
I was referring to a non-TRMS meter while measuring in the DC current mode. It measures the average value of the current.Not usually true. Switchers these days are cranking above 100 kHz, some above 1 MHz. TRMS meters don't measure accurately that high.
Most of the time the meters lean more toward catching peaks which means it will give a false higher reading. The easy way to clean it up is with a small L-C filter into the input port and measure the current on the outboard side of the L. I have had to do this a few dozen times.
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YES. It's why we always made sure use a filter to get the input current to smooth DC.Have you actually tried to do measurements without the LC filter and gotten significant errors in the measured DC current?
Not really. It might measure the average of an AC sine wave, but the input ripple to a switcher is not sinusoidal and not purely AC. It looks more like a sawtooth with asymmetric teeth width riding on DC level. What meters read in that case is not usually accurate. In most cases, the meters get the DC level and then pick up the peak of the AC on top of it, so it reads a little high.I was referring to a non-TRMS meter while measuring in the DC current mode. It measures the average value of the current.
In Figure 7, the triangular waveform represents the input current of a converter operating in PFM mode without the additional input capacitor . The straight waveform represents the input current when a capacitor is added across the input. If no capacitor is added, then the input current meter cannot accurately determine the amperage of the input current, because the input current has a large sinusoidal component. In contrast, adding a large capacitance across the input produces a steady current waveform, allowing the input current meter to accurately sense the amperage of the input current.
I have some 220uh coils on hand. Will they do? What is a "big cap"? How many mfds?Make an L-C filter. You can wrap maybe 20 turns of wire around a pencil to make an inductor. Put a big cap near the input of the device. Insert the ammeter on the power source side of the inductor.
That coil will work. Big cap means bigger the better, at least a few thousand uF or however much is available.I have some 220uh coils on hand. Will they do? What is a "big cap"? How many mfds?
It will run about 80-85% efficiency, with a typical inductor. A nice hand wound iron toroid might get you 85-90% with that IC.I am going to build a 12 - 5V step down buck regulator based on the MC34063.
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How do you hand wind and inductor if you do not have an LC meter? Is there a formula? Where do you get the cores?It will run about 80-85% efficiency, with a typical inductor. A nice hand wound iron toroid might get you 85-90% with that IC.
Those figures are assuming you use a decent external switch. If you use the 34063 internal switch transistor in buck you will get more like 75-80%.
If you don't have an inductance meter you should probably just use off the shelf inductors.How do you hand wind and inductor if you do not have an LC meter? Is there a formula? Where do you get the cores?
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I meant another transistor that is used as the main switch, this will have better performance than thetransistor inside the 34063. Circuits are all shown in the IC datasheet.... What do yo mean by "decent" external switch"? Is there another transistor that can be added to the 34063 circuit?