Technically all DC-DC converters at a minimum have an AC current in their input and output capacitances. Since we see a small ripple voltage across the capacitors, it must be true that the direction of the current flowing in the capacitors is alternating.
It is true that in most cases the inductor current isn't changing direction though.
The current is always positive except when it's turned off. It never reversed so it never passes through 0v to get to negative volts. Which is also the big advantage, since you're not spending part of the time at lower voltage.
Active rectifiers (ie. transistor based) are common in various high current applications. One quite weird example are line-interactive UPSes, which often use topology that allows same MOSFET bridge to be used as both rectifier when charging and frequency converter when discharging. Somewhat more representative application are various high current DC supplies, for example Vcore DC/DC converters on PC motherboards (12V DC -> <1V DC) almost invariably use active rectification.
> [1] Opposite is low voltage switching power supplies where the output voltage is low and currents are high. You see people use active diodes to avoid voltage drops despite the expense. Even then 90-95% efficiency is common.
Thanks, I din't know about this one at all. I should have paid more attention during the lectures, missed this part totally.
There isn't even any reactive current, it's just a non-sinusoidal load current because there is a rectifier and capacitors for smoothing the rectified voltage at the input.
The other place where I see a lot more linear regulators is inside ICs!
Working in Mixed Signal ICs and IP I see a lot of linear regulators.
Inductors are huge and (generally) off chip. If say your SOC has an AMS components, and PINs are a commodity, then you can't use anything but a Charge Pump and LDOs.
Well it does incorporate a voltage boost converter as part of it's operation but yeah, people have been doing that sort of thing since forever. Any time you have a requirement for a higher voltage than the supply and you are pulsing something this design will just fall out from that. Not an invention...
The Velodyne driver circuits are also entirely straightforward. The characteristics of inductors and capacitors are pretty well known by now. Apparently you can get a patent for using them in entirely obvious ways.
This article's explanation of a rectifier is incorrect. Most rectifiers used in real products are full bridge rectifiers which use both the positive and negative part of A/C.
Not sinusoidal: Boost and buck converters use PWM square waves. Because the power transistors are almost always fully on or fully off the I2R losses in the transistors are quite low.
If there's no inductor (and inductors are dangerous: see my other comment), then nothing on that PCB is pushing any current. Its all illusions created by "pulling" current.
> but you can of course design a circuit that will adjust voltage to keep current constant
So there's two designs and they're different in important ways. But first: the common part of _both_ designs is that the transistor is working as a "controlled resistor". The question is where you place this special resistor. The other commonality is that "negative-feedback" can configure this transistor to reach the appropriate resistance very easily.
So with the common stuff out of the way: we have two designs. "Series Regulator" and "Shunt Regulators" (traditionally voltage-regulators, but they could be current in practice. I'll discuss as if they're current regulators).
1. Series Regulator -- The transistor is treated as an adjustable resistor "in series" with the rest of the circuit. This "pinches down" the voltage/current to the level deemed acceptable to the engineer. Ex: If "downstream", you sense a 100-Ohm load and you have a target-current of 10mA, and your source voltage is 5V, you set the transistor so that its equivalent to 400-Ohms (total a 500-ohm system, so 10mA goes through).
But if the downstream circuit changes (a button was pressed and a motor is now being driven), and the downstream circuit now looks like a 10-Ohm load, to keep the constant 10mA current your Series-Regulator will automatically set the transistor to act like a 490-Ohm resistor (keeping the 500-ohm system, so 10mA remains constant).
2. Shunt Regulator -- The transistor is treated as an adjustable resistor "in parallel" with the rest of the circuit. This "diverts" excess energy to ground, causing the rest of the circuit to effectively function within its specifications. Ex: If "downstream", you sense a 100-Ohm load and you have a target-current of 10mA and your source current is 50mA, you set the transistor so that it is equivalent to 25-Ohms. This shunts 40mA to ground, and the remaining 10mA goes to the 100-Ohm load.
But if the downstream circuit changes (a button was pressed and a motor is now driven), and the downstream circuit now looks like a 10-Ohm load... to keep the constant 10mA current your Shunt-regulator will automatically set the transistor to act like a 2.5-Ohm load. This shunts 40mA to ground and the remaining 10mA goes to the 100-Ohm load.
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Traditionally, series and shunt regulators sense voltage (not current), but its not very difficult to turn a voltage-regulator into a current-regulator instead.
Series regulators are your typical 7905 or whatever. They are more efficient (as you can tell by their obvious operation) and simpler to use.
Shunt regulators are traditionally Zener Diodes, or other circuits that are based "like" a Zener Diode. They can generate constant voltage offsets reliably (ex: if you have a 9V line from a series regulator, and you need a 7V reference, you can use a shunt-regulator to very accurately create -2V).
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As you can see, its all "pulling tricks".
Of course, the switching regulator (Ex: MC34063. Don't use, this is an old chip lol. But maybe TI's Simple Switcher series, or similar), truly "push" current thanks to an externally supplied inductor... and as a result lead to far superior efficiency specs.
Another "pushing" trick is a charge-pump. You can turn on capacitors in such a way that they double the voltage. That's the thing about "pushing", you need an ability to increase voltage until the "downstream" circuit acts the way you like.
Inductors (and capacitors, to a lesser extent) _can_ push. But its dangerous and somewhat difficult to design well. (Fortunately, we have pre-made modules like TI's Simple Switcher or Microchip's MCP1640, etc. etc. that do the job for us automatically... as well as pre-made power supplies).
Fair enough, but as I mentioned these devices have both positive and negative slope in their V-I curves.
That said, where have you seen non-linearity in ordinary resistors? Just for grins a I pulled one out my parts drawer and threw it on the sweep generator on my bench. I could not identify any non-linearity in the sweep, it was simply a straight line between 0 to 10mA. Where are you seeing nonlinearity in your resistors?
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