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How Do I Find a Proper Voltage Regulator?

Author: Apogeeweb
Date: 1 Apr 2021
 1121
electronic voltage regulator

Introduction

A voltage regulator is a circuit that generates a fixed output voltage of a preset magnitude that remains constant regardless of changes to its input voltage or load conditions. It converts an unstable dc voltage into a stable dc voltage. Its power supply composed of discrete components has the advantages of large output power and wide adaptability. In recent years, integrated regulated power supplies have been widely used. Among them, three-terminal series regulators are the most common for low-power regulated power supplies. The commonly used integrated voltage regulators in the circuit mainly include 78xx series, 79xx series, adjustable integrated voltage regulator, precision voltage reference integrated voltage regulator, etc.

What is a Voltage Regulator and How Does It Work?

Catalog

Introduction

Ⅰ Voltage Regulator Classification

Ⅱ Main Parameters

Ⅲ Applying Notes

Ⅳ Typical Examples: LM317 & LM7805


Ⅰ Voltage Regulator Classification

Voltage regulators are generally divided into linear voltage regulator and switching voltage regulator. Linear voltage regulator is a circuit used to maintain a steady voltage, which is divided into low dropout type and general dropout type. Switching voltage regulator is a type of switch mode power supply circuit that is designed to efficiently reduce dc voltage from a higher voltage to a lower one, which is divided into step-down type, step-up type and integrated type with opposite input and output polarity.
According to the number of outlet terminals and usage of the voltage regulator, it can be roughly divided into three-terminal fixed type, three-terminal adjustable type, multi-terminal adjustable type and single-chip switch type.
The three-terminal fixed type voltage regulator integrates sampling resistors, compensation capacitors, protection circuits, high-power adjustment tubes, etc. on a chip. So that the entire integrated circuit block has only 3 terminals: input, output and public. It is very convenient to use. Its disadvantage is that the output voltage is fixed, so a series of products with various output voltages and current specifications must be produced to match.
The three-terminal adjustable integrated voltage regulator only needs two external resistors to obtain various output voltages.
The multi-terminal adjustable type is an early integrated voltage regulator. With small output power and many pins, it is not convenient to use, but the precision is high and the price is cheap.
The monolithic switch type integrated regulated power supply develops in recent years, and its efficiency is particularly high. Its working principle is different from the above three types. It is a converter that converts DC to AC (high frequency) and then DC. Usually there are two types of pulse width modulation and pulse frequency modulation, and the output voltage is adjustable.

monolithic 3-terminal positive voltage regulator LM7808

Ⅱ Main Parameters

1) Voltage Regulation Rate
It is an important indicator that characterizes the voltage regulation performance of the integrated voltage regulator, also known as the voltage regulation coefficient or stability. It represents how stable the output voltage V0 of the regulator is when the input voltage V1 changes.

2) Current Regulation Rate
It is also known as current stability coefficient, and shows the ability of the regulator to suppress output voltage fluctuations caused by changes in load current (output current) when the input voltage remains unchanged.

3) Ripple Rejection Ratio
It reflects the ability of the regulator to suppress the mains ripple voltage introduced at the input.

4) Output Voltage Temperature Coefficient
It is also known as the output voltage temperature change rate, and refers to when the input voltage and output current (load current) remain unchanged, the output voltage of the regulator changes with temperature.

5) Long-term Stability of the Output Voltage
It refers to the magnitude of the change in the output voltage value over time (when the output current, input voltage and ambient temperature remain unchanged). It is usually the maximum amount of change in the output voltage of the regulator within a specified time.

6) Output Noise Voltage
Its absolute value represents the noise performance of the regulator directly. There is also a percentage value of the output noise voltage Vn and the output voltage V0 of the regulator to characterize the noise performance.

7) Thermal Stability
It refers to the thermal stability of the voltage regulator. It is usually the percentage value of the relative change in the output voltage caused by its unit power consumption.

8) Temperature Stability
It is the percentage value of the relative change of the regulator's output voltage within the specified maximum change range of operating temperature.

 

Ⅲ Applying Notes

① There are many types of integrated voltage regulator. According to the adjustment method there are linear and switch type. Based on the output method, there are fixed and adjustable types. Because of the obvious advantages of the three-terminal voltage regulator, it is more convenient to use and operate.
② Before connecting to the circuit, it is necessary to distinguish the pins and their functions to avoid damage to the integrated block. The input and output ends of the three-terminal integrated voltage regulator with an output voltage greater than 6v need to be connected with protective diodes to prevent the rapid discharge of the output capacitor, which will cause damage to the three-terminal integrated voltage regulator when the input voltage drops suddenly.
③ In order to ensure the stability of the output voltage, the minimum input voltage difference should be guaranteed. For example, the minimum pressure difference of the three-terminal integrated voltage regulator is about 2v, and it should be kept above 3v during general use. At the same time, it should be noted that the maximum voltage difference of input and output does not exceed the specified range.
④ In order to expand the output current, the three-terminal integrated voltage regulator is allowed to be used in parallel.
⑤ When using, the welding should be firm and reliable. If a heat dissipation device is required, it should meet the required size.
If you have a bad regulator, it may cause many components such as the fuel pump, ignition system, or other parts which require a minimum amount of voltage to not function correctly. You may experience the engine sputtering, a rough idle, or simply a lack of acceleration when you need it.

 

Ⅳ Typical Examples: LM317 & LM7805

The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25V to 37V. It serves a wide variety of applications including local, on card regulation. This device can also be used to make a programmable output regulator, or by connecting a fixed resistor between the adjustment and output, the LM317 can be used as a precision current regulator.

LM317 Specifications

 LM317 voltage regulator

Adjustable output voltage as low as 1.2V

Output voltage: 1.25-37V DC

Guaranteed 1.5A output current

Output current: 5mA-1.5A

Typical linear adjustment rate: 0.01%

Max input-output voltage difference: 40V DC

Typical load regulation rate: 0.1%

Min input-output voltage difference: 3V DC

Ripple rejection ratio: 80dB

Operating temperature: -10± 85℃

Output short circuit protection

Storage temperature: -65± 150℃

Over-current, overheat protection

Output voltage: 1.25-37V DC

Adjusting tube safe working area protection

Output current: 5mA-1.5A


 

The linear voltage regulator LM7805 has over-voltage protection, over-current protection, and over-heat protection functions, which makes its performance very stable. It is a 5V regulator, and is able to achieve output current above 1A, and has a good temperature coefficient. So the product has a wide range of applications. Have a look to get more specific info by the following video:

Why is the LM7805 is a very Popular Voltage Regulator?

As a member of 78xx series of fixed linear voltage regulators, the following is a very good summary of the basics on linear voltage regulator 7805:

7805 typical circuit

Parameter

Symbol

Conditions

Min

Typical

Max

Unit

Output Voltage

Vo

Tj=25℃

4.8

5.0

5.2

V

5.0mA<Io<1.0A

Po<15W

Vi=7v to 20v

4.75

5.0

5.25

V

Linear Adjustment rate

△Vline

Tj=25℃, Vi=7V to 25V

 

3.0

100

mV

Tj=25℃

Vi=8V to 12V

 

1.0

50

mV

Load Adjustment Rate

△Vload

Tj=25℃,lo=5.0mA to 1.5A

 

 

100

mV

Tj=25℃

lo=250mA to 750mA

 

 

50

mV

Static Current

Iq

Tj=25℃

 

 

8

mA

Static Current Rate

△Iq

lo=5mA to 1.0A

 

 

0.5

mA

Vi=7V to 25V

 

 

0.8

mA

Output Voltage Drift

△Vo/△T

lo=5mA

 

-1.1

 

mV/℃

Output Noise Voltage

EN

f=10Hz to 100KHz

Tj=25℃

 

 

40

μV/Vo

Ripple Rejection Ratio

SVR

f=120Hz,Vi=8V to 18V

62

 

 

dB

Voltage Differential

Vd

lo=1.0A

Tj=25℃

 

2.0

 

V

Output Impedance

Ro

f=1KHz

 

17

 

Short-circuit Current

Isc

Vi=35V

Tj=25℃

 

750

 

mA

Peak Current

Iscp

Tj=25℃

 

2.2

 

A


If you want to make a 5V power supply with a 7805, output currents up to 1A can be drawn from the IC provided that there is a proper heat sink. A 9V transformer steps down the main voltage, 1A bridge rectifies it and capacitor C1 filters it and 7805 regulates it to produce a steady 5V DC. Then you can test it, turn on the DC power supply and adjust the output voltage of about 8V or slightly larger. Or alternatively you can use a battery 9V-12V as voltage source. Look at the voltmeter panel when you set the voltage. Prepare a DC voltmeter readings on voltage range 50V to measure the output voltage of the IC 7805.

 

Frequently Asked Questions about Voltage Regulator

1. What is voltage regulator and how it works?
A voltage regulator generates a fixed output voltage of a preset magnitude that remains constant regardless of changes to its input voltage or load conditions. ... A switching regulator converts the dc input voltage to a switched voltage applied to a power MOSFET or BJT switch.

 

2. What is a voltage regulator used for?
Voltage regulator, any electrical or electronic device that maintains the voltage of a power source within acceptable limits. The voltage regulator is needed to keep voltages within the prescribed range that can be tolerated by the electrical equipment using that voltage.

 

3. What are the three 3 basic types of voltage regulators?
There are three types of Switching voltage regulators: Step up, Step down, and Inverter voltage regulators.

 

4. What happens when voltage regulator goes bad?
If you have a bad regulator, it may cause many components such as the fuel pump, ignition system, or other parts which require a minimum amount of voltage to not function correctly. You may experience the engine sputtering, a rough idle, or simply a lack of acceleration when you need it.

 

5. Where are voltage regulators used?
Electronic voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant.

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Related Articles

pinglun 5 comments

    • pingluntus
    • RachelYe on 2021/6/7 15:47:20

    Hi, I have a 1978 FJ40 and the charging system stopped working last night on the ride home. The headlights flicked bright then dim a few times and finally stayed dim. I just checked the charging output and my volt meter said 11.4 VDC. How do I tell if I need the $35 voltage regulator or the $200 alternator?

      • pingluntu
      • author on 2021/6/11 10:01:21
        author

      Re:

      Hooking up with and oscilloscope would be the best method to determine the condition of your alternator and your regulator.🙂

    • pingluntus
    • Jackson on 2021/6/11 10:23:43

    Hello, I am building a field power supply that incorporates a lead acid car battery. When fully charged the battery shows a voltage of more than 13 volts. It is a 35Ah battery. I am using this battery to power 12 volt devices such as telescope tracking mount and a Surface Pro 4 computer/tablet that I use to drive the mount. I am not yet sure what amperage I may be needing but so far about 5 amp being available may be adequate. The tracking mount voltage is specified as 11 to 16 volt DC and its hunger level is at 4Amps. The computer, on the other hand, does not provide a range of DC input. We are just going by the fact that its AC power supply claims it is producing 12 volts DC. Henceforth I want to make sure to regulate the power output to the computer to 12 volt DC. I don’t imagine I need to limit how much amperage it would take in because that is really a function of the computer itself. But it does take something like 2.58 Amp. Can you point me to a product you have that I can easily incorporate into my design?

      • pingluntu
      • author on 2021/6/15 10:45:04
        author

      Re:

      In response to your question, any voltage regulator is going to have a limit on how much current it can handle. I’m sure there are regulators that meet your current draw requirements, but we do not have any step-up/step-down regulators that can handle more than about 2.5 A. We do have step-down regulators that can handle significantly more current, but I don’t think that would be a good idea for your application since a step-down regulator’s output voltage would drop along with the battery voltage once it falls below 12 V, and your computer might be sensitive to an undervoltage condition like that.

      I’ve always used my DIY power supply box for my cgem, dew heater, etc and never had a problem.  The DIY power supply box uses a 12v deep cycle marine battery attached directly to some 12v power sockets.
      my concern now is I just purchased a new Losmandy G11-g and I want to make sure I don’t damage it by not having the voltage regulator.  I also power my Atik Titan and dew heater with it.
      I think that you will need to check the manuals for the things that you want to attach to see if they can handle the full voltage of the nominally 12V battery which is more like 13.8V.
      Because most equipment designed to work with 12V power is expected to be hooked to a car battery, most of it will be rated up to 13.8 or even 15V, but you can't know until you check the manufacturer's information.

    • pingluntus
    • Gerrifessy Perthy on 2021/6/17 10:13:54

    Hi, I have an external hard drive that I hook up to my car stereo that runs off of 12V, rather than using a 12VDC to 120VAC inverter and then the supplied AC->DC converter like I have in the past, could I use a simple Zener Diode circuit to regulate the voltage down to 12V. Only use a Zener Diode with a forward current of 12V (example)? I'd have to size the resistor accordingly, the HDD states it consumes ~15 watts of power. I'd use a voltage regulator like the 7812, but they wouldn't work if the car was off and running close to 12V, they drop out around 13.7V or so.

      • pingluntu
      • author on 2021/6/18 10:33:22
        author

      Re:

      While a 7812 will not work, as you've stated... I have used LM317 variable regulators @ 12 volt in car with success. Even with the car off, a healthy battery should be approx 12.6v
      I used these to prevent dimming of LED lighting in vehicles with high draw stereo systems. (Example, LED license plate lights dimming durring a bass note.)
      To power a hard drive however, you might need something larger like an LM150? Having never tried one @ 12v out on a car circuit... I can't say what the working minimum input voltage would need to be...

    • pingluntus
    • Kelven on 2021/7/2 17:33:05

    I'm looking for recommendations for a 12 volt regulator that will work with out a battery. I added hand warmers and upgraded my alternator coil and now have 36 vac. About 40 volts DC after my bridge rectifier and 3 1000u capacitors. I tried a buck converter and it work for 10 minutes and died. Have you ever try using a regulator for and older snowmobile that would not be equipped with a starting battery? I would prefer to be right around 14 volts DC, hand warmers get nice and toasty.

      • pingluntu
      • author on 2021/7/3 14:54:00
        author

      Re:

      Usually if you have 36 VAC, you will only have half of that in DC, it would be more like 18 VDC or less, more down around 14.8 VDC the way most stator coils are wound.
      A lot of regulators rely on sensing battery voltage to give them a base point or something to first sense the voltage so they can use that to regulate the output.
      Years ago Honda did make special voltage regulators for the older XR Off-Road series motorcycle that had the headlight rated at 6VAC. The regulator was used to install a 12VDC light bulb.
      It was a very small regulator rectifier unit.
      I remember putting one on a '84 XR250R model. It was a Hondaline accessory. I don't know if they are available anymore due to the age. They were used to power both the headlight and tail light. That motorcycle did not use a battery. 🤔

    • pingluntus
    • Kinsley on 2021/7/28 14:25:25

    Hi, Something related to it, I am trying to select a DC/DC non-isolated converter that will work with 12V or 24V DC input voltage. The Vout should be 19V DC and the output current 0.5A I guess that a buck/boost converter could maintain the output voltage in both cases, 12V or 24V of input voltage. My concern is when the input voltage is 12V because it is 7V below the required 19V of output. Is a buck/boost converter a suitable component for this application?

      • pingluntu
      • author on 2021/7/29 11:59:15
        author

      Re:

      A buck/boost can either buck or boost as required, depending on the duty cycle of the switch, so it is the obvious choice for this application.
      One thing to note about the buck/boost is that the output is either inverted or referenced to the positive rail. Most applications require a positive voltage referenced to the negative rail, and for this reason, a flyback is often used instead of a buck boost, with the extra winding on the magnetic providing inversion. 
      TI devices such as the UCC28c42 or UCC28c43 can be easily configured to drive such a circuit.

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