Download: DC Current PWM-Controller. Circuit Engineering
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DC Current PWM-Controller. Circuit Engineering. Pulse-width modulation is a method of voltage control that today is used quite extensively. PWM-signals are for the most part used to control motors and pulse power supply units. This purpose is served by a number of control circuits: transistors, special microcircuitry, digital signal processors. As a rule, a transistor, often a FET, is used to control the generated PWM-signal. Widely popular are the width-pulse circuits that control powerful field-effect transistors - MOSFETs. These transistors are capable of switching high current of up to 100A and above at the gate voltage of 12-15V. The on-state transistor resistance is very low, which decreases the dissipated power. Control circuits are supposed to provide for at least 12V-15V difference between the gate and the source. In some cases, PWM-controllers employ microchips with output voltage build-up of up to 25-30V at 8-14V supply voltage, which facilitates connection of the transistor in the circuit with the common drain. For the majority of loads with current consumption of below 10A the circuits do not have an additional voltage build-up unit. Let's look at an example of PWM-controller using a simple circuit based on the logical CMOS microchip inverters. The device is a square-wave generator based on two logical components, where the diodes separately change the electric charge time constant and the electric discharge time constant of the capacitor that sets the frequency. It is this property that enables changing the output pulse ratio and the value of the output voltage on the load. The circuit uses an inverting CMOS component K561LN2, a field-effect transistor that should better be applied with peak current, since it has a lower on-state resistance. This helps decrease the dissipated power and use a cooler with a smaller footnote. The main benefit of this circuit is the simplicity of the structure and reliability of operation.