1.5V to 5V boost converter circuit for microcomputer

Here is a 1.5V to 5V boost converter circuit. Why it is interesting. Now, small electrical appliances have a microcomputer that requires the 5V power supply and low current less than 10mA.

The 1.5V AA battery is cheap and popular. How we can use it as a power supply of that tiny microcomputer.

Sure, we have many ways to step-up voltage. Using ICs may be a good idea. But If we are beginners or who love experiment basic circuits.

In this circuit, we use only small transistors.

1.5V to 5V boost converter circuit using transistors for microcomputer
1.5V to 5V boost converter circuit using transistors for microcomputer


This circuit is one of 5 DC converters using small transistors. All circuits  are so easy to learn and having fun.

  1. DC to DC Buck converter working principle
  2. Switch mode LED driver circuit (Save energy)
  3. USB 5V to 12V DC-DC Step-Up Converter circuit
  4. Simple 12V transistor switching power supply
  5. 1.5V to 5V boost converter circuit for microcomputer
  6. 5V to +/- 12V boost converter circuit or higher using transistor

You should read all for more understanding.

How it works

Also, we can use the nickel-cadmium/nickel-metal hydride battery of 1.2V, alkaline battery to these appliances.

The microcomputer requires a low current power supply. This 1.5V to 5V boost converter circuit is small.

So, it can be in the game players, MP3 portable, DVD players.

This 1.5V to 5V boost converter circuit as above is applied from this boost converter into a new circuit.

The basic circuit of DC to DC boost converter

Learn how this works

If you got it, Read next

Single output version

step up converter 12V 5V

See in the circuit below. It is the single output (5V 10mA) version.

1.5V to 5V Boost DC Converter circuit using 2 transistors
1.5V to 5V Boost DC Converter circuit using 2 transistors

The important is Q1, L1, and D1 like the previous circuit. But additional the Zener diode ZD1 is regulation to makes the stable output.

This circuit converts the 1.2V or 1.5V input voltage up to the 5V.  While it can apply the current of 10 mA. This current level is sufficient for the general microcomputer.

Small LCD display Supply(Dual Voltage)

However, some appliances may have an LCD display inside. For example, game players, MP3 players, etc. 

They require the -5V power supply.

We can do it easily. It becomes 5V Dual power supply, +5V at 10mA, and -5V at 0.5mA (approximately).

Look at the circuit below.

1.5V to +/-5V DC Converter circuit using 2 transistors for LCD display
1.5V to +/-5V DC Converter circuit using 2 transistors for LCD display

We add C4, D2, and D3. They are the simple charge pump converter, to make a negative voltage, -5V. The current of this section is about 0.5 mA.

How the circuit works

First of all, apply the current(1.5V battery) to the circuit. The current cannot flow through L1. Because Q1 does not get the bias current.

Then, Q2 starts working with the current from 1.5V. And, the current flows from the emitter to the base of Q2 through R5 to be the full circuit.

The Q2 provides the current out of the collector to be a biased current to Q1. The Q1 is conducting.

You may like to see these too.

Now, the L1 connects to the ground like a normal boost converter. But the working of Q1 makes the voltage across collector-emitter is lower. They work looks like a switch.

So, It will add quality conducting of Q2, with R3 and C2. Make this system is high performance. Also, Q1 is good working.

And, the L1 passes the high current until the maximum in linear form. After that, the polarity of the voltage across L1 changes.

The performance of this circuit is about 60%.  The advantage of this circuit.  The voltage drop across it is low.

While the transistor switch on the voltage across between collector-emitter is only 0.2V. But it can supply the high current.

Parts you will need

0.25W Resistors, tolerance: 5%
R1, R4: 470K
R2, R3: 100Ω
R4: 2.2K

Ceramic Capacitors
C2: 10nF (0.01µF) 50V
C4: 0.1µF 50V

Electrolytic Capacitors
C1,C5: 10µF 25V
C3: 1µF 25V

Semiconductors and others:
Q1: BC547 or BC550, 45V 0.1A, NPN TO-92 Transistor
Q2: BC557 or BC560, 45V 0.1A, PNP TO-92 Transistor
D1,D2,D3: 30V 200mA, Schottky Diode
ZD1: 5.1V 0.5W Zener Diode
L1: 270uH coil, 200mA See cheap coil

This circuit we can use many transistor like: BC546/BC547/BC548/BC549/BC550 for NPN type.
BC556/BC557/BC558/BC559/BC560 for PNP type.

This concept optimizes the performance of the power supply circuit.

Keep reading:

Credit: LCD display photo

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I always try to make Electronics Learning Easy.

Apichet Garaipoom

I love the electronic circuits. I will collect a lot of circuit electronics to teach my son and are useful for everyone.
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