Timeline for Energy of flyback with multiple outputs
Current License: CC BY-SA 4.0
21 events
| when toggle format | what | by | license | comment | |
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| Feb 9, 2021 at 14:15 | vote | accept | Jonathan | ||
| Feb 2, 2021 at 14:42 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Feb 2, 2021 at 14:31 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Feb 2, 2021 at 14:22 | comment | added | Andy aka | @MathKeepsMeBusy OK, you've convinced me - I shall make an amendment. | |
| Feb 2, 2021 at 14:21 | comment | added | Math Keeps Me Busy | @Andyaka The same principles apply. In DCM, the energy transfered in one cycle depends upon duty. But in CCM, the energy transfered in one cycle depends not only on duty, but on the residual current through the inductor from the previous cycles. | |
| Feb 2, 2021 at 14:21 | comment | added | Andy aka | @MathKeepsMeBusy it's a buck converter so it's not really relevant here though. Maybe you might be right for a flyback in CCM? | |
| Feb 2, 2021 at 14:14 | comment | added | Math Keeps Me Busy | Yes, if there is a sudden change in load, there will be a transient change in voltage. But it is not true that for a fixed frequency and duty cycle, there is a fixed output current or power, and the only way to increase it is to increase duty cycle. Not only does that contradict the well known formulae for the relationships between voltage and duty cycle, but we can empirically verify that for the same duty cycle we can have different output currents and output powers. Anyone can simulate the circuit provided in the answer linked to above. | |
| Feb 2, 2021 at 14:09 | comment | added | Andy aka | @MathKeepsMeBusy that's not true. I have thought about this. In CCM, if the load current is too high (a sudden transient) then we increase duty cycle (a little) and, in effect, we create a situation where the average current rises and things then stabilize back to the same duty cycle but with a higher average current to match energy per cycle to the power requirements of the load. For a buck converter, an increased load current naturally causes the average current in CCM to rise; it's a little less clear in a flyback converter because energy transfer is disconnected from energy charge. | |
| Feb 2, 2021 at 14:05 | comment | added | Math Keeps Me Busy | "And, you only get more energy per cycle by increasing the duty cycle." This is true when the SMPS is in discontinuous conduction mode, but is not true in continuous conduction mode. See my answer to a related question. | |
| Feb 2, 2021 at 13:38 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Feb 2, 2021 at 12:51 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Feb 2, 2021 at 12:44 | comment | added | Andy aka | @user253751 if the length of time that the green line is falling cannot sustain all the load currents then the output voltage must drop and then, the duty cycle needs to increase to allow a higher energy transfer per switching cycle. It's not the same current - it slopes downwards until it hits zero (DCM) or the switching cycle begins again (CCM). | |
| Feb 2, 2021 at 12:35 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Feb 2, 2021 at 12:33 | comment | added | Criticizing Israel not allowed | @Andyaka don't you draw the same current from the transformer no matter what the load is (but for more or less time, according to the chart)? But when you add more taps, you draw more current? | |
| Feb 2, 2021 at 12:29 | comment | added | Andy aka | @user253751 that's not really true except when dealing with load changes i.e. transients. Once the load has stabilized, the slope of the green line is related to the output voltage and the equivalent secondary inductance. | |
| Feb 2, 2021 at 12:27 | comment | added | Andy aka | @Jonathan that formula applies when the device is operated in CCM mode. On light loads, the flyback is highly likely to be in DCM mode. In CCM mode the load changes are dealt with by the overall current waveforms rising or falling and so power does increase to suit the load(s). | |
| Feb 2, 2021 at 11:58 | comment | added | Criticizing Israel not allowed | @Jonathan Higher output current from the transformer (note: not the PSU output current) affects the slope of the green line. If you draw more current in total, the line goes to 0 faster. | |
| Feb 2, 2021 at 11:55 | comment | added | Jonathan | But flyback transfer function is Vo/Vi = n*D/(1-D) (where D is the duty cycle, and n is the windings ratio), so if we keep Vo and Vi constant, we can derive the duty cycle. But you say that different loads change the Duty cycle, but the whole point is keeping constant Vo, Vi (and therefore constant Duty cycle), so how is it logical? | |
| Feb 2, 2021 at 11:54 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Feb 2, 2021 at 11:36 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Feb 2, 2021 at 11:23 | history | answered | Andy aka | CC BY-SA 4.0 |