![]() ![]() ![]() The ripple picked by the oscilloscope is 0.8 volts. The average value indicated by the voltmeter is 5.58 volts. Here it is again on a smaller time scale: Wave shape in Q 1's drain - the rising edge, the falling edge dropping below zero, the storage interval and transition intervalĪfter the low-pass filtering stage a smoother signal is produced. The aforementioned is time given by the sum of the storage and transition intervals. This is known as reverse recovery time and it is specific to diodes. Instead, on the falling edge the signal drops below the zero level, remains at a constant level for a moment and then slowly gets back to zero. The output of this stage should have been the amplified version of the PWM signal generated by the MCU. Probing the MOSFET's drain yields a new imperfect wave shape. Wave shape in Q 1's drain - a distorted 3.125% duty cycle PWM signal, attenuated by a 1/11 factor To counteract them, one should minimize stray capacitances and inductance and that in itself is another long story. The only explanation, at this stage, is that the parasitic impedances around the switching circuit are opposing the ideal propagation of the signal through the system. The MOSFET's gate charges just as fast as it discharges but it is the sudden closing of the Q 1 that creates a small voltage overshot. Wave shape in Q 1's gate - a closer look at the distorted 96.875% duty cycle PWM signal, attenuated by a 1/11 factor Changing the R 1 to match the R 2 doesn't change the shape of the signal. That could be explained by the fact that R 2 is twice the value of the R 1 and that the Q 2 has a non-negligible ON resistance. It appears that the Q 1 is not opened as fast as it gets closed. Wave shape in Q 1's gate - a distorted 96.875% duty cycle PWM signal, attenuated by a 1/11 factor Expectedly, it should have the same shape. Let's now take a look at the signal in the Q 2's gate. The signal in Q 2's collector is the inverted version of the one generated by the Arduino. have port 3 generate a 8/256 = 3.125% duty cycle PWM signalĪnd the effect in Q 2's collector: Wave shape in Q 2's collector - a 96.875% = 1 - 3.125% duty cycle PWM signal, attenuated by a 1/11 factor The Atmega164's pin 3 was chosen for providing the signal and here's the code behind it: The schematics above omits the 15 volt input power source, the 8 Ohms consumer and the Arduino board generating the PWM signal. C 1 capacitor acts as a near-by energy buffer that charges from the power source when the main switching transistor Q 1 is off and discharges onto the RLC branch when Q 1 is on. The device uses a flyback diode D 1 that creates a path for the induced current to flow when the switch, Q 1, is off. Last but not least, the L 1 inductor and the C 2 capacitor are forming with the consumer a RLC low-pass filter which attenuates the voltage ripple generated by the first function. The first is done by the Q 1 MOSFET which is power-opened by the Q 2 bipolar transistor and passively closed by the R 1 resistor. Proposed here fulfills two main functions: chopping the input voltage and smoothing out the result. This article lays out a quick application of the principle using a P-Channel MOSFET and an Arduino board. The function is detailed on Wikipedia but concisely, the converter uses a PWM signal to chop the input voltage and the result is fed to the consumer through a LC low-pass filter. Try a search in this forums and you may find the details.The Buck or Step-Down converter is an electric circuit that takes a higher input voltage and gives a lower voltage at the output, with minimal power loss. There was a very good Arduino based MPPT charger around some years ago by Tim Nolan, which shows the basics of how to build one. The aim of the exercise is to continuously monitor the input power to keep it as high as possible, and there are various algorithms that do this. To do this, you need part of the circuitry of a buck converter, but not all of it, and some additional circuitry to measure input power to the controller, usually a current sensor of some kind and voltage sensor. Normal buck converters are designed to provide a stable output voltage regardless of what the input voltage is, and to do this they provide a tight feedback loop between the output voltage and the comparator in the switcher.Ī MPPT type controller isnt designed to provide a stable output voltage, but is designed to provide a variable load to match the peak power point of a solar panel as its shifts around with varying levels of illumination. If you are trying to make an MPPT type controller, a conventional buck converter is not what you want. ![]()
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