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You are here: Home / Power Supply Circuits / Making 3.3V, 5V Voltage Regulator Circuit with Diodes and Transistors

Making 3.3V, 5V Voltage Regulator Circuit with Diodes and Transistors

Last Updated on May 2, 2020 by Swagatam 33 Comments

In this post we learn to make 3.3V, 5V voltage regulator circuits from higher voltage sources, such as 12V or a 24V source without ICs.

Linear ICs

Normally a step down voltage from a higher voltage source is obtained by using a linear IC such as a 78XX series voltage regulator IC or a buck converter.

Both the above options can be costly and/or complex options for getting a particular desired voltage quickly for a particular application.

Zener Diodes

Zener diodes also become useful when it comes to achieving a lower voltage from a higher source, however you cannot get sufficient current from a zener diode voltage clamp. This happens because zener diodes normally involve a high value resistor for protecting itself from high currents, which restricts the passage of higher current to the output to just milliamps, which mostly becomes insufficient for an associated load.

A quick and a clean way to derive a 3.3V or 5V regulation or any other desired value from a given higher voltage source is to use series diodes as shown in the following diagram.

Using Rectifier Diodes for Dropping Voltage

In the above diagram we can see about 10 diodes being used for acquiring a 3V output at the extreme end, while other corresponding values can also be seen in the form of 4.2v, 5v and 6V levels across the relevant dropping diodes.

We know that typically a rectifier diode is characterized to drop around 0.6V across itself, meaning any potential fed at a diode's anode will generate an output at its cathode which would be normally approximately 0.6V less than the input at its anode.

We take the advantage of the above feature in order to achieve the indicated lower voltage potentials from a given higher supply.

Using 1N4007 Diode for 1 Amp Current

In the diagram 1N4007 diodes are shown which might yield not more than 100mA, although 1N4007 diodes are rated to handle upto 1amp, it needs to be ensured that the diodes do not begin warming up, otherwise that would result in higher voltages being allowed to pass.

Because as the diode heats up the rated drop across it begins receding towards zero, that's why not more than a 100mA max  should be expected from the above design for preventing over heating and enabling an optimal response from the design.

For higher currents one may opt for higher rated diodes such as 1N5408 (0.5amp max) or 6A4(2amp max) etc.

The drawback of the above design is that it does not produce accurate potential values at the output and therefore might not be suitable for applications where customized voltage references may be needed or for applications where the load parameter could be crucial in terms of its voltage specs.

For such applications the following configuration could become very desirable and useful:

Using an Emitter Follower BJT

The diagram above shows a simple emitter follower configuration using a BJT and a few resistors.

The idea is self explanatory, here the pot is used for adjusting the output to any desired level right from 3V or lower to the maximum fed input level, although the maximum available output would be always less than 0.6V than the applied input voltage.

The advantage of incorporating a BJT for making 3.3V or 5V regulator circuit is that it enables you to achieve any desired voltage using minimum number of components.

It also allows higher current loads to be used at the outputs, moreover the input voltage has no restrictions and may be increased as per the BJT's handling capacity and by some minor tweaks in the resistor values.

In the given example, an input of 12V to 24V can be seen, which can be tailored to any desired level such as to 3.3V, 6V, 9V, 12V, 15V, 18V, 20V or to any other intermediate value simply by flicking the knob of the included potentiometer.

SHARING IS CARING!



Previous: Adjustabe CDI Spark Advance/Retard Circuit
Next: SMPS Voltage Stabilizer Circuit

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

You'll also like:

  • 1.  Low-Dropout 5V, 12V Regulator Circuits using Transistors
  • 2.  1.5V to 12V DC Converter Circuit for LEDs
  • 3.  IC 723 Voltage Regulator – Working, Application Circuit
  • 4.  Designing Simple Power Supply Circuits
  • 5.  Variable Voltage, Current Power Supply Circuit Using Transistor 2N3055
  • 6.  DC to DC Converter Circuits using SG3524 [Buck, Boost Designs]

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  1. Search Related Posts for Commenting

  2. Raj says

    Hi Swagatam,
    For this circuit, my input is tapped from secondary transformer of 20-0 AC.
    If I use rectifying it will produce some 28Vdc. How can I modify to suit this voltage please.
    I need to drive a 5vdc relay in delay mode.

    Thank you

    Reply
    • Swagatam says

      Hi Raj, no need of using a full bridge rectifier at the transformer output. You can use a single diode 1N4007, and use the output for feeding the transistor emitter follower circuit. At the emitter side of the transistor you can connect the relay, and connect a 1000uF/25V parallel to the relay coil.
      You can replace the 10K preset with a 7V zener diode.

      Reply
  3. nitin chaudhari says

    Sir, If I use 7805 and diodes to drop Voltage from 9v to 3v , what about heating problem and power consumption ?

    Reply
    • Swag says

      Nitin, Heating of 7805 cannot be avoided, otherwise you may have to make a buck converter circuit.

      Reply
  4. nitin chaudhari says

    Hi sir, I want to run small 3v motor . Can I use Voltage divider with 150ohm and 100ohm resistor to drop voltage upt 3.6v with 70mA current?
    Or please suggest another good way to do it.
    Thanks in advance.

    Reply
    • Swag says

      Hi Nitin, what is the input voltage? Is it 12V?

      Anyway you can drop the voltage by using the last concept explained above, or you can also use an LM338 IC variable voltage regulator to adjust the output to 3V.

      Resistor divider will not work, because resistors will waste a lot of power and also will not be able to provide sufficient current to the motor.

      Another simple idea would be to use a 7805 IC and 3 series diodes in series with its positive output

      Reply
  5. Adams says

    Sir, i wanted to use the voltage drop across a rectify diode to regulate my 12v source to about 10.6 or 10.8v at 3A current, but you just explain the drawback to this configuration, please which other configuration will be suitable for me, because my resultant voltage must be stable because of the sensitivity or my load.

    Reply
    • Swag says

      Adams, you can try the transistorized circuit, and feed the supply from a 7812 IC, the output will be fairly accurate.

      Reply
      • Adams says

        Yes sir, the Transistorize circuit will work better, but the current will be an issue. i am looking at a 3A current source but as explained, the transistor can handle 0.5A. What can i do, sir

        Reply
        • Swag says

          Adams, TIP122 is actually rated to handle upto 5 amps, so you can expect it to work easily with 3 amp current just make sure to mount it on a good heatsink

          Reply
          • Adams says

            Thank you sir.

            Reply
  6. jindro says

    gud am Sir! I’m I really love your projects, I pray that u will continue in experimenting and discovering new circuits that is really really helpful for many of your follower like me 🙂 Sir is heat sink necessary for the second circuit? for tip122 or tip142?

    Reply
    • Swag says

      Thank you jindro, yes heatsink will be required if the load current rating is above 500mA

      Reply
  7. kokoilie says

    Can I use this schematic to step down from 24V (truck battery) to 19V at about 5A(the high current is needed to charge the laptop battery) or do I need to replace some components?
    -hobby/newbie at electronics here

    Reply
    • Swagatam says

      yes you can… try the transistor option, replace the TIP122 with a TIP142 for 5 amp limit

      Reply
    • kokoilie says

      Thank you for the quick reply, I'll try it as soon as I get the components.

      Reply
  8. Malware Zero says

    Sir do you have a 12v to 5v buck conv using 555 timer ckts, using my inverter to 12v SLA-battery consume a 10w of power even in no load situation. 🙁

    Reply
    • Swagatam says

      You can try the second circuit from the following link:

      https://homemade-circuits.com/2015/10/calculating-inductor-value-in-smps.html

      Reply
  9. kanta says

    Hi Swagatam,
    What are the wattage of the resistor on the collector and base respectively Thanks
    Regards
    Kanta

    Reply
    • Swagatam says

      Hi Kanta,

      when wattage is not mentioned it's always 1/4 watt

      Reply
  10. Manoharan Chinnaiyan says

    Hi Sir,

    I feel this may be a silly question to you. But I am new and just wanted to know the purpose of 1k & 10k resistors at the output in both the circuits?
    Can you pl explain?

    Reply
    • Swagatam says

      Hi Manoharan.

      the 1K resistor is for biasing (triggering) the transistor into conduction, while the 10K resistor is just to tie-up the emitter of the transistor to a ground reference which actually is not essential and may be avoided.

      Reply
    • Manoharan Chinnaiyan says

      Thanks much sir.

      Reply
  11. MUJAHID SHAH says

    sir what is outboard transistor? and what is the current capacity of lm196

    Reply
    • Swagatam says

      Mujahid,

      please refer to the following article, the first diagram shows T1 connected as an outboard transistor while the second diagram shows how to use an LM196 transistor.

      https://homemade-circuits.com/2012/05/make-this-voltage-stabilizer-circuit.html

      LM196 will provide you with 10amp current

      Reply
  12. MUJAHID SHAH says

    sir i want to handle 10 amp load with voltage regulator. so I want to know can I use two or three lm338 parallel controlling with single variable? is it possible? or any other solution. thank you

    Reply
    • Swagatam says

      you can replace LM338 with a LM196, or you can use an outboard transistor with LM338 for increasing its current capacity.

      Reply
  13. MUJAHID SHAH says

    can I replace tip122 with to-3 package transistor like the one 2n3055 or any for higher current

    Reply
    • Swagatam says

      yes you can do it, but for optimal current you may have to reduce the base resistors value accordingly ( wattage may increase significantly)

      Reply
  14. MUJAHID SHAH says

    I made a transformerless timer circuit with ic555. I used 0.1uf cap to drop voltage including 12v zener diode to get 12v supply. I did not use a resistor in series with zener diode. the circuit worked well for a few days but then zener got damaged. is it because that I did not use a resistor in series with zener or I used zener diode that was unable to support load.
    as you have stated above we cannot get sufficient current from zener diode

    Reply
    • Swagatam says

      I think you have used 1uF and not 0.1uF….anyway, yes it's because you did not use a limiting resistor in the circuit…but the resistor must be in series with the input supply not in series with the zener. use a 1watt zener diode, and if possible connect a 1N4007 in parallel to the zener diode.

      Reply
  15. MUJAHID SHAH says

    sir I tried the second circuit and its very nice regulating voltage. sir what about the circuit with ic lm338

    Reply
    • Swagatam says

      Mujahid, LM338 circuit is the standard, traditional way of regulating voltage, but it's much complex and expensive than the above concepts

      Reply



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