WHAT IS RICOH DRIVER
The mechanism can be explained from the perspectives of the output driver On-resistance and the output load resistance ratio. Then, how do linear regulators control the resistance of the driver transistor to output a stable voltage, even when the load current (load resistance) or the input voltage fluctuates? As resistors are fabricated and located in a considerably small area inside a semiconductor chip, the resistance ratio becomes highly accurate. It represents that the output voltage is determined simply by the reference voltage and the resistance ratio of the feedback voltage at a normal state.Īccording to this equation, too, it can be said that the voltage reference (VREF) is the key component which determines the characteristics of a linear regulator.Īlso, the variability of the resistance values does not matter, because the output voltage is determined by the resistance ratio of R1 and R2. This equation does not consider the input voltage nor the load current (load resistance). Thanks to the reference voltage unit keeping a certain level of a reference voltage, linear regulators can output a fixed voltage.
Reference voltage units can maintain a certain voltage level despite the fluctuations in the input voltage or the changes in the ambient temperature. It is depicted in Figure 3 with a battery symbol. Its output voltage level is from about 0.6 to 1.0 V. It features a small circuit size and an extremely low supply current. A CMOS-based reference unit uses the difference between the threshold voltage of two MOS transistors as a reference voltage. Instead of BGRs, more electronic equipment utilizes a CMOS-based voltage reference unit. 1.25V is a commonly used output voltage level for a BGR. Although this method has good characteristics, its supply current and circuit structure tend to be larger, for it utilizes the voltage between the base and the emitter of a bipolar transistor. There are some methods to construct a reference voltage unit, and most of them provide an output voltage level of around 1 V.Ī conventional method used for a reference voltage unit is called a band gap reference (BGR). 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. 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.
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