Timeline for How Does a Buck Converter Maintain a Constant Voltage?
Current License: CC BY-SA 4.0
8 events
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| Jan 27, 2021 at 11:40 | comment | added | Verbal Kint | Well, in a perfect buck converter operated in CCM voltage-mode at a constant switching frequency, the duty ratio and the output voltage are theoretically independent of the load current: \$V_{out}=DV_{in}\$. However, if you account for the losses incurred to the inductor ohmic resistance \$r_L\$, the MOSFET \$r_{DS(on)}\$, the diode \$V_f\$ and so on then yes, the loop compensates these losses by adjusting the duty ratio. If you are interested to further dig, please see my article on the subject. | |
| Jan 27, 2021 at 10:30 | comment | added | Bimpelrekkie | Yes, you're getting it :-) | |
| Jan 27, 2021 at 10:30 | comment | added | RGB Engineer | Ok it's starting to make sense now. The duty cycle controls the average current through the inductor. The average current through the inductor is determined by the load. Thus, is we increased the load, we would increase the duty cycle. | |
| Jan 27, 2021 at 10:24 | comment | added | Bimpelrekkie | Yes/no, you're comparing 5V to 10 V. That's confusing as the DuCy is also related to the difference between input and output voltage. It is easier to state: A 1.0 Ampere load will require a different duty cycle than a 1.2 Ampere load (assuming everything else remains the same). | |
| Jan 27, 2021 at 10:19 | comment | added | RGB Engineer | I think I understand what you're saying. A 10V output voltage across a 10 ohm load will require a different duty cycle than a 5V output voltage across a 5 ohm load, is that correct? | |
| Jan 27, 2021 at 10:16 | comment | added | Bimpelrekkie | I thought that duty cycle directly controlled the output voltage though? When the load is constant then yes, the DuCy would directly influence the output voltage. But the opposite is more useful, we keep the output voltage constant by changing the DuCy. For a constant load, that DuCy would remain constant. However you don't know what DuCy you need for a specific output voltage as that depends on the load. That's why the feedback loop is needed, to generate "whatever PWM signal is needed" to keep the output voltage at a specific value. | |
| Jan 27, 2021 at 10:12 | comment | added | RGB Engineer | I thought that duty cycle directly controlled the output voltage though? Wouldn't a change in duty cycle thus change the output voltage? | |
| Jan 27, 2021 at 10:08 | history | answered | Bimpelrekkie | CC BY-SA 4.0 |