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Because that is NOT the role of the diode. You are thinking of a protection diode across a relay or solenoid coil. A switching regulator is something completely different.
When the switch is opened, the left side of the inductor tries to go very negative. When the voltage gets to one diode drop below ground, it is caught at by the diode when it starts to conduct. This holds the left side of the inductor firmly just below ground. The inductor's magnetic field still is collapsing, so since the left side can not go more negative, the right side goes positive, discharging the inductor into the capacitor.
In a block diagram of a buck converter, the input to the inductor is connected to two switches, one to the DC input (the upper switch) and one to GND (the lower switch). Whenever one switch is on the other is off. In practice, the upper switch always is an active device like a bipolar transistor or MOSFET. For low cost, the lower switch can be a diode. It needs no control circuitry because the actions of the upper switch and the inductor automatically bias the diode into on and off states at the correct times. For greater efficiency, the lower diode is replaced with another transistor that does required a properly times control signal. This is called a synchronous buck converter.
ak
When the switch is opened, the left side of the inductor tries to go very negative. When the voltage gets to one diode drop below ground, it is caught at by the diode when it starts to conduct. This holds the left side of the inductor firmly just below ground. The inductor's magnetic field still is collapsing, so since the left side can not go more negative, the right side goes positive, discharging the inductor into the capacitor.
In a block diagram of a buck converter, the input to the inductor is connected to two switches, one to the DC input (the upper switch) and one to GND (the lower switch). Whenever one switch is on the other is off. In practice, the upper switch always is an active device like a bipolar transistor or MOSFET. For low cost, the lower switch can be a diode. It needs no control circuitry because the actions of the upper switch and the inductor automatically bias the diode into on and off states at the correct times. For greater efficiency, the lower diode is replaced with another transistor that does required a properly times control signal. This is called a synchronous buck converter.
ak
Last edited:
Arouse1973
Adam
Another name for this diode is a free wheeling diode.
Thanks
Adam
Thanks
Adam
Ok so the diodes job is to hold the left side to ground because it becomes negatively charged, and if the diode was not there?
The left side would become neg charged but the right would still peak and the voltage would still pass through the diode, as the circuit emulator implies but the diode is purely to keep the negative spike grounded then? And this helps efficiency how?
(Thanks, and no i was not thinking of flyback diode to act as supression across an inductor)
The left side would become neg charged but the right would still peak and the voltage would still pass through the diode, as the circuit emulator implies but the diode is purely to keep the negative spike grounded then? And this helps efficiency how?
(Thanks, and no i was not thinking of flyback diode to act as supression across an inductor)
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Arouse1973
Adam
The inductor is the supplier of energy and the diode supplies the path for this energy to flow in a loop. It does also clamp the flyback voltage from the coil which could otherwise damage the switching device.
Adam
Adam
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