Simple Multiple Voltage Regulator

 Simple Multiple Voltage Regulator

Five years ago when I first started with the Arduino and Raspberry Pi I did not think too much about power supply, at this time the power adapter from the raspberry Pi and the USB supply of Arduino was more than enough.

But after some time my curiosity pushed me to consider other power supply methods, and after creating more projects I was forced to make considerations about different and if possible adjustable DC power sources.

Especially when you finish your design you will definitely want to build a more permanent version of your project, and for that you will need to consider how to go about providing power to it.

In this Tutorial I will explain how you can create your own linear power supply with widely used and affordable voltage regulators IC (LM78XX, LM3XX, PSM-165 etc.). You will learn about their functionality and implementation for your own projects

Design considerations

Common Voltage Levels

There are several standard voltage levels that your design might require:

3.3 Volts DC – This is a common voltage used by Raspberry PI and low-powered digital devices.

5 Volts DC – This is the standard TTL (Transistor Logic) voltage used by digital devices.

12 Volts DC – used for DC, servo and stepper motors.

24/48 Volts DC – widely used in CNC and 3D Print projects.

You should consider in your design that logic level voltages need to be regulated very precisely. For example for devices with TTL voltage the supply voltage needs to be between 4.75 and 5.25 volts, otherwise any voltage deviation will cause the logic components to stop working correctly or even destroy your components.

In contrast to the logic level devices the power supply for the motors, LEDs and other electronic components can deviate in a wide range. Additionally you must consider current requirements of the project. Especially motors can cause the current draw to fluctuate and you need to design your power supply to accommodate the “worst case” situation where every motor is operated at full capacity.

You have to use different approaches for the voltage regulation for the line powered and battery powered designs, because the battery voltage levels will fluctuate as the battery discharges.

Another important aspect of the voltage regulator design is the efficiency – especially in battery powered projects you must reduce power losses to the minimum.

ATTENTION: In most of the countries a person cannot legally work with voltages above 50V AC without a license. Any mistake made by any person working with lethal voltage can lead to their own death, or that of another person. For this reason I will only explain DC power supply build with voltage level under 60 V DC.

Types of Voltage Regulators

There are two main types of voltage regulators:

 linear voltage regulators which are most affordable and simple to use

switching voltage regulators which are more efficient than linear voltage regulators, but more expensive and they require a more complex circuit design.

In this tutorial we will work with linear voltage regulators.

Electrical characteristics of the linear voltage regulators

The voltage drop in the linear regulator is proportional to the dissipated power of the IC, or in other words power loses because of the heating effect.

For the power dissipation in the linear regulators following equation can be used:

Power = (VInput – VOutput) x I

The L7805 linear regulator has to dissipate at least 2 watts if it would deliver a 1 A load (2 V voltage drop times 1 A).

With the increase of the voltage difference between the input and output voltage - the power dissipation also increases. Meaning, for example, while a 7 volts source regulated to 5 volts delivering 1 amp would dissipate 2 watts through the linear regulator, a 12 V DC source regulated to 5 volts delivering the same current would dissipate 5 watts, making the regulator only 50% efficient.

The next important parameter is the “Thermal Resistance” in units of °C/W (°C per Watt).

This parameter indicates the number of degrees the chip will heat up above the ambient air temperature, per each watt of power it must dissipate. Simply multiply the calculated power dissipation by Thermal Resistance and that will tell you how much that linear regulator will heat up under that amount of power:

Power x Thermal Resistance = Temperature Above Ambient

For example a 7805 regulator has a Thermal Resistance of 50°C / Watt. This means if your regulator is dissipating:

1 watt, it will heat up 50°C

.2 watts it will heat up 100°C.

NOTE: During project planning phase try to estimate required current and reduce the voltage difference to a minimum. For example 78XX linear voltage regulator has 2 V voltage drop (min. input voltage is Vin = 5 + 2 = 7 V DC), as a result you can use 7,5 or 9 V DC power supply.

Efficiency calculation

Under consideration that the output current is equal to the input current for a linear regulator then we will get simplified tion:

Efficiency = Vout / Vin

For example, let’s say you have 12 V on the input and need to output 5 V at 1 A of load current, then the efficiency for a linear regulator would only be (5 V / 12 V) x 100% = 41 %. This means that only 41% of the power from the input is transferred to the output, and the remaining power will be lost as heat!

The 78XX voltage regulators are 3-pin devices available in a number of different packages, from large power transistor packages (T220) to tiny surface mount devices it is a positive voltage regulators. The 79XX series are the equivalent negative voltage regulators.

The 78XX series of regulators provide fixed regulated voltages from 5 to 24 V. The last two digits of the IC part number denote the output voltage of the device. This means, for example, a 7805 is a positive 5 volt regulator, a 7812 is a positive 12 volt regulator.

These voltage regulators are straight forward – connect L8705 and a couple of electrolytic capacitors across the input and output, and you build a simple voltage regulator for 5 V Arduino projects.

The important step is to check the data sheets for the pin-outs and manufacturer recommendations.

The 78XX (positive) regulators use the following pinouts:

INPUT—unregulated DC input Vin

REFERENCE (GROUND)

OUTPUT -regulated DC output Vout

One thing to note about the TO-220 case version of these voltage regulators is that the case is electrically connected to the center pin (pin 2). On the 78XX series that means the case is grounded.

This type of linear regulator has a 2 V dropout voltage, as a result with a 5V output at 1A, you need to have at least 2.5 V DC head voltage (i.e., 5V + 2.5V = 7.5V DC input).

The manufacturer recommendations for the smoothing capacitors is CInput = 0.33 µF and COutput = 0.1 µF, but general practice is 100 µF capacitor on the input and the output It is a good solution for the worst-case scenario, and the capacitors help to cope with sudden fluctuations and transients in the supply.

In the case that the supply falls below the threshold of 2 V- the capacitors will stabilize the supply to ensure that this does not happen. If your project does not have such transients, then you can run with the manufacturer's recommendations.

Simple linear voltage regulator circuit is just L7805 voltage regulator and two capacitors, but we can upgrade this circuit to create some more advanced power supply with some level of protection and visual indication.

If you would like to distribute your project then I will definitely suggest to add those few additional components in order to prevent future inconvenience with customers.

First you can use the switch to power the circuit on or off.

Additionally you can place a diode (D1), wired in reverse bias between the output and input of the regulator. If there are inductors in the load, or even capacitors, a loss of input can cause a reverse voltage, which can destroy the regulator. The diode bypasses any such currents.

Additional capacitors act as a kind of final filter. They must be voltage rated for the output voltage, but should be high enough to suit the input for a little margin of safety (e.g., 16 25 V). They really depend on the type of load you expect, and can be left out for a pure DC load, but 100uF for C1 and C2, and 1uF for C4 (and C3) would be a good start.

Additionally you can add the LED and appropriate current-limiting resistor to provide an indicator light which is very useful for power supply failure detection; When the circuit is powered LED lights are ON otherwise look for some failures in your circuit.

Most voltage regulators have protection circuitry that protects chips from overheating and if it gets too hot, it drops the output voltage and therefore limits the output current so that the device is not destroyed by the heat. Voltage regulators in TO-220 packages also have a mounting hole for the heatsink attachment, and I will suggest that you should definitely use it to attach a good industrial heatsink.

Most of the 78XX regulators are limited to an output current of 1 - 1.5 A. If the output current of an IC regulator exceeds its maximum allowable limit, its internal pass transistor will dissipate an amount of energy more than it can tolerate, which will lead to the shutdown.

For applications that require more than the maximum allowable current limit of a regulator, an external pass transistor can be used to increase the output current. Figure from FAIRCHILD Semiconductor illustrates such a configuration. This circuit has the capability of producing higher current (up to 10 A) to the load but still preserving the thermal shutdown and short-circuit protection of the IC regulator.

 Simple Multiple Voltage Regulator

Five years ago when I first started with the Arduino and Raspberry Pi I did not think too much about power supply, at this time the power adapter from the raspberry Pi and the USB supply of Arduino was more than enough.

But after some time my curiosity pushed me to consider other power supply methods, and after creating more projects I was forced to make considerations about different and if possible adjustable DC power sources.

Especially when you finish your design you will definitely want to build a more permanent version of your project, and for that you will need to consider how to go about providing power to it.

In this Tutorial I will explain how you can create your own linear power supply with widely used and affordable voltage regulators IC (LM78XX, LM3XX, PSM-165 etc.). You will learn about their functionality and implementation for your own projects

Design considerations

Common Voltage Levels

There are several standard voltage levels that your design might require:

3.3 Volts DC – This is a common voltage used by Raspberry PI and low-powered digital devices.

5 Volts DC – This is the standard TTL (Transistor Logic) voltage used by digital devices.

12 Volts DC – used for DC, servo and stepper motors.

24/48 Volts DC – widely used in CNC and 3D Print projects.

You should consider in your design that logic level voltages need to be regulated very precisely. For example for devices with TTL voltage the supply voltage needs to be between 4.75 and 5.25 volts, otherwise any voltage deviation will cause the logic components to stop working correctly or even destroy your components.

In contrast to the logic level devices the power supply for the motors, LEDs and other electronic components can deviate in a wide range. Additionally you must consider current requirements of the project. Especially motors can cause the current draw to fluctuate and you need to design your power supply to accommodate the “worst case” situation where every motor is operated at full capacity.

You have to use different approaches for the voltage regulation for the line powered and battery powered designs, because the battery voltage levels will fluctuate as the battery discharges.

Another important aspect of the voltage regulator design is the efficiency – especially in battery powered projects you must reduce power losses to the minimum.

ATTENTION: In most of the countries a person cannot legally work with voltages above 50V AC without a license. Any mistake made by any person working with lethal voltage can lead to their own death, or that of another person. For this reason I will only explain DC power supply build with voltage level under 60 V DC.

Types of Voltage Regulators

There are two main types of voltage regulators:

 linear voltage regulators which are most affordable and simple to use

switching voltage regulators which are more efficient than linear voltage regulators, but more expensive and they require a more complex circuit design.

In this tutorial we will work with linear voltage regulators.

Electrical characteristics of the linear voltage regulators

The voltage drop in the linear regulator is proportional to the dissipated power of the IC, or in other words power loses because of the heating effect.

For the power dissipation in the linear regulators following equation can be used:

Power = (VInput – VOutput) x I

The L7805 linear regulator has to dissipate at least 2 watts if it would deliver a 1 A load (2 V voltage drop times 1 A).

With the increase of the voltage difference between the input and output voltage - the power dissipation also increases. Meaning, for example, while a 7 volts source regulated to 5 volts delivering 1 amp would dissipate 2 watts through the linear regulator, a 12 V DC source regulated to 5 volts delivering the same current would dissipate 5 watts, making the regulator only 50% efficient.

The next important parameter is the “Thermal Resistance” in units of °C/W (°C per Watt).

This parameter indicates the number of degrees the chip will heat up above the ambient air temperature, per each watt of power it must dissipate. Simply multiply the calculated power dissipation by Thermal Resistance and that will tell you how much that linear regulator will heat up under that amount of power:

Power x Thermal Resistance = Temperature Above Ambient

For example a 7805 regulator has a Thermal Resistance of 50°C / Watt. This means if your regulator is dissipating:

1 watt, it will heat up 50°C

.2 watts it will heat up 100°C.

NOTE: During project planning phase try to estimate required current and reduce the voltage difference to a minimum. For example 78XX linear voltage regulator has 2 V voltage drop (min. input voltage is Vin = 5 + 2 = 7 V DC), as a result you can use 7,5 or 9 V DC power supply.

Efficiency calculation

Under consideration that the output current is equal to the input current for a linear regulator then we will get simplified tion:

Efficiency = Vout / Vin

For example, let’s say you have 12 V on the input and need to output 5 V at 1 A of load current, then the efficiency for a linear regulator would only be (5 V / 12 V) x 100% = 41 %. This means that only 41% of the power from the input is transferred to the output, and the remaining power will be lost as heat!

The 78XX voltage regulators are 3-pin devices available in a number of different packages, from large power transistor packages (T220) to tiny surface mount devices it is a positive voltage regulators. The 79XX series are the equivalent negative voltage regulators.

The 78XX series of regulators provide fixed regulated voltages from 5 to 24 V. The last two digits of the IC part number denote the output voltage of the device. This means, for example, a 7805 is a positive 5 volt regulator, a 7812 is a positive 12 volt regulator.

These voltage regulators are straight forward – connect L8705 and a couple of electrolytic capacitors across the input and output, and you build a simple voltage regulator for 5 V Arduino projects.

The important step is to check the data sheets for the pin-outs and manufacturer recommendations.

The 78XX (positive) regulators use the following pinouts:

INPUT—unregulated DC input Vin

REFERENCE (GROUND)

OUTPUT -regulated DC output Vout

One thing to note about the TO-220 case version of these voltage regulators is that the case is electrically connected to the center pin (pin 2). On the 78XX series that means the case is grounded.

This type of linear regulator has a 2 V dropout voltage, as a result with a 5V output at 1A, you need to have at least 2.5 V DC head voltage (i.e., 5V + 2.5V = 7.5V DC input).

The manufacturer recommendations for the smoothing capacitors is CInput = 0.33 µF and COutput = 0.1 µF, but general practice is 100 µF capacitor on the input and the output It is a good solution for the worst-case scenario, and the capacitors help to cope with sudden fluctuations and transients in the supply.

In the case that the supply falls below the threshold of 2 V- the capacitors will stabilize the supply to ensure that this does not happen. If your project does not have such transients, then you can run with the manufacturer's recommendations.

Simple linear voltage regulator circuit is just L7805 voltage regulator and two capacitors, but we can upgrade this circuit to create some more advanced power supply with some level of protection and visual indication.

If you would like to distribute your project then I will definitely suggest to add those few additional components in order to prevent future inconvenience with customers.

First you can use the switch to power the circuit on or off.

Additionally you can place a diode (D1), wired in reverse bias between the output and input of the regulator. If there are inductors in the load, or even capacitors, a loss of input can cause a reverse voltage, which can destroy the regulator. The diode bypasses any such currents.

Additional capacitors act as a kind of final filter. They must be voltage rated for the output voltage, but should be high enough to suit the input for a little margin of safety (e.g., 16 25 V). They really depend on the type of load you expect, and can be left out for a pure DC load, but 100uF for C1 and C2, and 1uF for C4 (and C3) would be a good start.

Additionally you can add the LED and appropriate current-limiting resistor to provide an indicator light which is very useful for power supply failure detection; When the circuit is powered LED lights are ON otherwise look for some failures in your circuit.

Most voltage regulators have protection circuitry that protects chips from overheating and if it gets too hot, it drops the output voltage and therefore limits the output current so that the device is not destroyed by the heat. Voltage regulators in TO-220 packages also have a mounting hole for the heatsink attachment, and I will suggest that you should definitely use it to attach a good industrial heatsink.

Most of the 78XX regulators are limited to an output current of 1 - 1.5 A. If the output current of an IC regulator exceeds its maximum allowable limit, its internal pass transistor will dissipate an amount of energy more than it can tolerate, which will lead to the shutdown.

For applications that require more than the maximum allowable current limit of a regulator, an external pass transistor can be used to increase the output current. Figure from FAIRCHILD Semiconductor illustrates such a configuration. This circuit has the capability of producing higher current (up to 10 A) to the load but still preserving the thermal shutdown and short-circuit protection of the IC regulator.