This page partially uses JavaScript. This page may not operate normally when these functions are not supported by your browser or the setting is disabled.
Please look for the information you need from the following pages:

Asia-Pacific - English

Asia-Pacific - 简体中文

Asia-Pacific - 繁體中文

Asia-Pacific - 한국어

Asia-Pacific - 日本語

Americas - English

Europe (EMEA) - English

1-9. Differences between a three-terminal voltage regulator and an LDO regulator

Classic three-terminal voltage regulators (also known as standard voltage regulators) use an NPN-type transistor or an N-channel MOSFET as an output transistor.
For these regulators to work, an input-output voltage differential called a dropout voltage (V_DO) is necessary as shown below. In the case of NPN-type voltage regulators, the minimum value of V_DO must satisfy V_IN - V_OUT > R_IN x I_IN + 2 × V_BE.

Figure 1.9.1 circuitry diagram( VDO = VIN - VOUT = RIN x IIN + 2 x VBE )

In the case of MOSFET-based voltage regulators, the minimum value of V_DO must satisfy V_IN - V_OUT > R_IN × I_IN + V_GS. Suppose R_IN = 1 kΩ, I_IN = 1 mA, V_BE = 0.7 V, and V_GS = 1 V. Then, the minimum input voltage required to generate a 5-V output is calculated to be 7.4 V in the case of NPN-type voltage regulators and 7 V in the case of MOSFET-based voltage regulators.

Figure 1.9.2 circuitry diagram( VDO = VIN - VOUT = RIN x IIN + VGS )

Figure 1.9.3 circuitry diagram( VDO = VIN - VOUT = VCE(sat) and VDO = VIN - VOUT = VDS )

In contrast to these regulators, LDO regulators mainly use a PNP transistor or a P-channel MOSFET as an output transistor. The minimum dropout voltage of such LDO regulators is determined by the collector-emitter voltage (V_CE(sat)) and the drain-source voltage (V_DS = R_DS(ON) × I_D). Therefore, LDO regulators can operate with a smaller dropout voltage than three-terminal voltage regulators.

Figure 1.9.4 a new type of LDO regulator that provides an even smaller dropout voltage

There is also a new type of LDO regulator that provides an even smaller dropout voltage, which uses an N-channel MOSFET with a smaller on-resistance than a P-channel MOSFET as an output transistor and has a power supply pin dedicated to the control circuit (including the MOSFET drive circuit).