Now that we have the energy per pulse, we can calculate the inductance using the input current and the energy: So if the output of our converter is 30 Watts, then we can say that the output energy is thirty Joules every second. Since it is easier to talk about inductors in terms of energy, we can assume now that the output power is simply the output energy per second. Now divide the output power by the selected switching frequency in order to get the power transferred per pulse. This is also the input power, by the law of conservation of energy (though not exactly so – nothing is a hundred percent efficient!). The duty cycle of the converter is given by:ĭetermine the output power, that is, the product of the output voltage and current. These two steps keep repeating many thousands of times a second, resulting in continuous output.ĭetermine the input voltage and the output voltage and current. This voltage is allowed to charge the capacitor and power the load through the diode when the switch is turned off, maintaining current output current throughout the switching cycle. Since the current in an inductor cannot change suddenly, the inductor creates a voltage across it. Since the voltage across the capacitor cannot rise instantly, and since the inductor limits the charging current, the voltage across the cap during the switching cycle is not the full voltage of the power source. The switch turns on and lets current flow to the output capacitor, charging it up. The working of a buck converter can be broken down into a few steps. The inductor resists changes in current and the capacitor resists changes in voltage, which results in the output being smooth DC.Īnd now we have a converter that is capable of stepping down DC voltages and doing it efficiently! To fix this problem, we turn to another type of voltage filter, the LC filter, which does the same job as the RC filter but replaces the R with an L, in other words the resistor with an inductor. We could now simply use this as a buck converter, but there’s one major drawback –the resistor in the RC filter limits the current and wastes energy in the form of heat, which is no better than the linear voltage regulator example. The below graph shows the raw PWM signal in blue color and the filtered outputs in red and violet color. The voltage level of the filter depends on the duty cycle of the PWM signal – the higher the duty cycle the higher the output voltage. Of course, connecting an RC filter to a square wave source renders the output clean. A small duty cycle means that the average voltage seen by the load is small and when the duty cycle is high the average voltage is high too.īut average voltage is not what we need – a raw PWN signal oscillates between high voltage level and ground, something no delicate load (like the microcontroller) would like. We’ve all heard of lights being dimmed by a PWM signal. The working of Buck converter is slightly similar to that of PWM ‘dimming’. The switch will be switched (turned on and off) by using a PWM signal. The switch shown in the above circuit will normally be a power electronics switch like MOSFET, IGBT or BJT. It’s quite similar to a boost converter, but the placement of the inductor and transistor are switched. A typical buck converter circuit is shown in the above image. It’s a type of DC-DC converter, so it accomplishes the task using a few transistor switches and an inductor. Luckily such a device already exists, and it’s called a buck converter or step down voltage regulators. Now we feel the pressing need to find something that can step DC voltages down and do it efficiently! Normally Linear voltage regulators has very low efficiency compared with switching regulators. If we calculate the efficiency, which is just output power divided by the input power, it comes out to be a pathetic 38%!. The power dissipated comes out to be around 8.7 Watts! Now this is a LOT of power for a little linear regulator to dissipate. If we calculate the power dissipated by the regulator: LEDs easily consume around 20mA each, so a long strip would easily eat up an amp or so. Now, suppose we have to power an LED strip from the same 3.3V rail. We have already learnt the working of Voltage regulators in our previous article. The solution is simple, we just add a 3.3V linear regulator IC like LD1117 with the 12V rail and it regulates the voltage down to 3.3V. For example we may need to power a 3.3V microcontroller from a 12V supply rail. Many a times in the electronics world we find the need to reduce one DC voltage to a lower one.
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