Difference between LDO and Switching Regulator

LDO

  • LDO is Low dropout regulators which is used for low voltage and ampere rating operations. For example – In laptop motherboard there are various sections which have different low voltage requirements like 1 V, 2 V, 3.3 V, 5 V, 6 V etc. These low voltage requirements can be easily fulfilled with the help of LDO regulator.
  • LDO are used for current ratings upto 100 mA, it implies if the load current requirement is increased then for maintaining current in the load there is voltage drop and increase in power dissipation in the LDO regulators which causes instability and power loss in the system.
  • Basic structure and diagram of an LDO internal circuit is shown in the diagram shown below.

Switching Regulator

  • Switching Regulators are used for high as well as low voltages and ampere rating operations. For example – In electronics system like laptop’s motherboard you require voltages of higher values like 15 V, 19 V, 24 V etc. These power supplies are not directly connected to the load. 
  • Switching regulators can be used for all the current ratings starting from 1 mA (1.05 V regulator in PCH section) upto 30 A (V Core voltage used for the VRM section of the motherboard) for electronics circuits. It is independent of the variation in the load. For any load voltage is maintained at constant value.
  • The diagram below shows the working method of a Switching regulator.
LDO
LDO
Voltage regulator
Voltage regulator

WORKING OF LDO

  • The  working principle of LDO is very simple. It’s input voltage is just slightly greater than the required output voltage. It can be seen from the above diagram of LDO (Low dropout), as the load is increased i.e the current flowing through the LDO is increased with the extra load demand then the variable resistance of the linear regulator gets decreased and hence maintaining the same voltage drop ( V=I*R ohms law) across it. So, the voltage at the terminal is maintained at a constant value upto a certain load demand after the load demand is increased above the rated value then the LDO will not be able to maintain the required output voltage.
  • Below is the commonly used LDO in the IC package.

WORKING OF REGULATOR

  • The working principle of switching regulator is a very interesting and requires some technical knowledge. Unlike LDO voltage regulators require PWM switching for maintaining constant voltage at the output terminal. The input voltage of these regulators are much greater than that of an LDO e.g for maintaining an output voltage of 3.3 V input supply required is 19 v. In case of a regulator as the load is increased (i.e current is high) then to maintain the same output voltage the regulator ic will trigger the PWM switching module who’s “duty cycle” can be manipulated to maintain the required output voltage and meet the load requirement.
  • The image below shows the Voltage regulator in IC package.
LDO IC
Voltage regulator
Regulator IC
  • In LDO no PWM switching is required Is has simple architecture and working philosophy. No external components (Switching MOSFETs, capacitors etc) are required for generating the desired value of the output voltage. 
  • In case of faulty LDO it can be checked with simple multimeter, whether the required inputs ( i.e Input voltage and Enable signal) are available in it’s proper form or not.
  • Voltage regulators are basically a “BUCK REGULATOR” that converts higher voltage into lower level. Voltage regulators are interchangeably also known as the “SWITCHING REGULATORS” because they require PWM switching signals at the GATE of the Switching MOSFETs as shown in the diagram to generate the desired value of the output. The output voltage decides the “DUTY CYCLE” of the PWM signal for the MOSFETs. Watch the video below to understand the duty cycle.
  • In case of faults in regulators they require multimeter as well as CRO/DSO oscilloscope for the testing of the PWM triggering signal.

VIDEO OF DUTY CYCLE