The divided voltage is called a feedback voltage (VFB). Feedback ResistorĪ feedback resistor (RFB) is named after its role of dividing the output voltage with two resistors (R1 and R2) and returning the divided voltage to an error amplifier.
#Power transistor voltage regulator driver#
Linear regulators maintain a fixed output voltage by regulating the resistance of the driver transistor with a controlling circuit (shown in Figure 1) composed of a feedback resistor, a reference voltage unit, and an error amplifier. This transistor is equivalent to the variable resistor shown in Figure 1.Īs is shown in Figure 2, where the load and input currents are equal at 100 mA, the VIN pin supplies all the current flowing through the driver transistor and the VOUT pin to the load. Output Driver Transistorįigure 3 is an example of a linear regulator constructed with a MOS transistor. The roles of each components are as follows: 1. For example, in the case of load current at 100 mA, a 5 V input and 2 V output regulator consumes 0.3 W of 0.5 W input electric power inside as heat.įigure 3. The current flowing inside the load resistor goes on to flow to the variable resistor, where the electricity is consumed with some heat generated.įigure 2 illustrates these relationships. The difference between the higher input voltage and lower output voltage will generate heat which is called waste heat. The input voltage is divided by the two resistors, so linear regulators generate a lower output voltage than their input voltage. For instance, if the input voltage (VIN) is fixed, a linear regulator can maintain a stable output voltage by keeping the ratio between the variable resistance value and the load resistance value fixed according to the changing rate of the load resistance value. The figure illustrates that the controlling circuit supervises the output voltage and regulates the resistance value of the variable resistor so that the IC can output the set fixed voltage. Simplified Internal Structure of Linear Regulator The controlling circuit monitors Vout and adjusts resistance value of the variable resistor so that the linear regulator can generate a fixed output voltage.įigure 1.
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