Types of Power Supply ICs

What is a power supply?

Personal computers, AV equipment, and other common electronic devices incorporate a number of electronic components in order to realize the functions of those devices. "Power supply" is the name given to the functional block that supplies the voltage or current required to operate the electronic components.



Broadly speaking, the power supply block performs the following two functions.

- Converts alternating current to direct current
- Converts direct current to direct current

These functions are explained below.

1. Conversion of alternating current to direct current

[Why conversion is necessary]
The electricity supplied to this power supply block is the electricity that is supplied from the power station to the power outlets of the office or house where the electronic device is being used. This electricity is 100 V AC in Japan. On the other hand, most of the components in an electronic device operate on direct current and a low voltage (such as 3.3 V or 1.8 V). In other words, the alternating current from the power outlets must be converted into direct current in order for the electronic device to operate.

For more information on alternating and direct current, see "Please explain the meanings of the units used to measure electricity" in the Electricity section of the Basic Knowledge FAQ.

[Role]
The role of the power supply block is to convert the alternate current from the power outlets into the direct current required by the electronic components.
The power supply IC in this power supply block is used to convert the rectifying circuit output to the required stabilized DC voltage.



2. Conversion of direct current to direct current

[Why conversion is necessary]
These days, consumers are demanding smaller and more power efficient electronic devices. This means that the power supply block must also be more compact and reduce power consumption and heat. Switching power supplies have been developed to satisfy these demands.
The electricity supplied from another source such as a battery is limited to a specific DC voltage (for example 12 V) and such supply situation is unstable. On the other hand, the various electronic components incorporated in electronic devices require different voltages (for example, 3.3 V and 1.8 V), accuracies, and capacity of currents, and abovementioned power source does not satisfy these power supply specifications of electronic components. Therefore, here too, conversion is required.
For more information on switching regulators, see "System Differences" in the Types of Power Supply ICs section under Power Supply IC in the Linear IC FAQ.




[Role]
The power supply block also has the function of converting the unstable voltage supplied from the battery to the stable voltage required by electronic components. A switching regulator, which is one type of power supply IC, can reduce heat generated by the conversion.
In the DC-DC conversion diagram shown in the next figure, the power supply IC has the function of converting the unstable DC voltage including ripples into the required stable DC voltage.

(2006/04)

How many types of voltage conversion are there?

There are 3 types of voltage conversion.

Related FAQ items
System Differences
Basic Configuration Example
Basics

(2006/07)

How do power ICs differ depending on the type?

Power supplies are classified according to their voltage regulation method as follows, and ICs for various applications are available.

Linear regulator

Function:To continuously control the voltage between the input and output so that an unstable input voltage is lowered and converted into a stable voltage output.



Type:Series regulators (such as 3-terminal regulators) and shunt regulators are available.
A series regulator that operates even if the difference between the input voltage and output voltage is approximately 1 V is called low-dropout type (LDO type).
Features:Simple because it's almost integrated into one chip as a power supply.

Switching regulator

Function:Controls ON/OFF of input and outputs a constant voltage by using a smoothing circuit.


Type:Insulated type (AC-DC converter) and non-insulated type (DC-DC converter) are available.
Application:Used as an AC-DC converter for stepping up, stepping down, or inverting the voltage, or as a DC-DC converter.
Features:Little heat emission and high efficiency. Suitable for a large power supply.

What are the major differences between series regulators and shunt regulators?

The major difference is in how the regulator is connected with the load in order to control the output voltage.
A series regulator is connected in series with the load to stabilize the regulator's output voltage. A shunt regulator, on the other hand, is connected in parallel to the load to stabilize the device's output voltage.

(2006/04)

What is a 3-terminal regulator?

This is the basic form of a series regulator and consists of three pins: input, GND, and output, hence its name.

What is a 3-terminal low dropout regulator?

In a general 3-terminal regulator (uPC78L00 Series, etc.), an NPN-type transistor is Darlington-connected in the output stage. The I/O voltage differential required for operation therefore cannot be lower than the voltage between the base and emitter of the Darlington-connected output stage transistor (0.7 V × 2 = 1.4 V).
In a 3-terminal low dropout regulator, a PNP transistor is used as the output stage transistor, so the device can be used with a small I/O voltage differential.



The power dissipation (Pd) in a 3-terminal regulator is expressed as follows.
P_d= (V_IN-V_O) ·I_O+V_IN·(I_bias+ΔI_bias1)
(V_IN-V_O) : I/O voltage differential
I_O: Output current
I_bias: Quiescent current
ΔI_bias1: Quiescent current change
The smaller the I/O voltage differential (V_IN-V_O), the smaller the power dissipation (heat generation).

Caution A large-capacity capacitor (at least 47 uF) is required at the output of a 3-terminal low dropout regulator to prevent abnormal oscillation.
Consequently, a comparatively large circuit operating current flows when the input is low, such as at startup. This peak current appears when the output voltage rises, so we do not recommend using this kind of regulator in applications in which a resistor is inserted at GND to shift up the output voltage.

(2006/12)

What is a variable-output 3-terminal regulator?

This is a regulator whose output voltage can be changed according to the value of an externally attached resistor. A variable-output 3-terminal regulator is used when a voltage is required that cannot be obtained from a fixed-output 3-terminal regulator. The output voltage of a variable-output 3-terminal regulator can be very finely adjusted, making this regulator very useful when a precise voltage is required.

What is a series regulator with ON/OFF function?

This is a series regulator that is a 3-terminal regulator with a control signal added to enable voltage to be output and stopped via an external logic signal.

What is a series regulator with 2 output functions?

This is a series regulator that outputs two different output voltages from an input voltage (in single package).

Example: The UPC37Mxx Series consists of regulators that have two output functions, OUTPUT1 (3.3 V or 2.5 V): 1 A and OUTPUT2 (1.8 V or 2.5 V): 0.5 A.

(2006/10)

The part numbers of some series regulators have a letter in the middle, such as "uPC78L05". How do these products differ?

This letter indicates the approximate output current characteristics of the series regulator (click here for details).

L: 0.1 A
N: 0.3 A
M: 0.5 A
(No symbol): 1.0 A

(2006/03)