# How to amplify 5V to 15V using a Base Common Amplifier

#### zarabotkalesna

Joined Nov 22, 2015
18
Hi guys! I want to amplify 5V to 15V using a Base Common Amplifier (because it has a high voltage gain), but I'm not succeeding... Cah you please help me? Thanks in advance.

#### Papabravo

Joined Feb 24, 2006
21,225
Doesn't look like a Common Base configuration to me. am I missing something?

#### zarabotkalesna

Joined Nov 22, 2015
18
I think it's it. Feel free to change anything and give me some suggestions!

Please note that the input signal is DC (USB 5V source), not AC.

Last edited:

#### bertus

Joined Apr 5, 2008
22,277
Hello,

The circuit is a common base circuit.
The Base is AC grounded by the 1 uF capacitor.
I assume the 5 Volts source on the right is the signal input.
It will NOT amplify the DC voltage as shown.
It also will never reach 15 Volts on the output as the powesupply shown on the lefty is only 5 Volts.

Bertus

#### ScottWang

Joined Aug 23, 2012
7,400
Ib1 = 1.36 mA - 1.34 mA = 0.02mA
I_2.46K = 1.57 mA
I_728Ω = 1.56 mA
Ib2 = 0.01 mA
So why the Ib1(0.02 mA) ≠ Ib2 (0.01 mA)?

#### Alec_t

Joined Sep 17, 2013
14,316
The cap on the emitter of the transistor will block your 5VDC 'input signal'.
You can't get 15V out of that amplifier, since its supply voltage is only 5V.

#### Papabravo

Joined Feb 24, 2006
21,225
I think it's it. Feel free to change anything and give me some suggestions!

Please note that the input signal is DC (USB 5V source), not AC.
I guess that's because all the grounded base circuits I've worked with had the base connected to GND or Vcc. I thought that blocking the supply on the right didn't make much sense as well.

#### zarabotkalesna

Joined Nov 22, 2015
18
Hello,

The circuit is a common base circuit.
The Base is AC grounded by the 1 uF capacitor.
I assume the 5 Volts source on the right is the signal input.
It will NOT amplify the DC voltage as shown.
It also will never reach 15 Volts on the output as the powesupply shown on the lefty is only 5 Volts.

Bertus
So, is there a way that I can use my USB port as an input (which is DC), and how much voltage should I apply as Vcc (on the left in my circuit)?

#### bertus

Joined Apr 5, 2008
22,277
Hello,

What kind of signal do you expect from the USB to amplify?
It will not be an AC signal, like audio.

Bertus

#### Alec_t

Joined Sep 17, 2013
14,316
So, is there a way that I can use my USB port as an input (which is DC)
In a word, no: unless you are prepared to build a switch-mode inverter?

#### zarabotkalesna

Joined Nov 22, 2015
18
Hello,

What kind of signal do you expect from the USB to amplify?
It will not be an AC signal, like audio.

Bertus
I want a DC signal in both input and output.

#### bertus

Joined Apr 5, 2008
22,277
Hello,

Then you would need a boost regulator as Alec_t also mentioned.
Keep in mind that the power output will NEVER be more than the input power.
There will ALWAYS be losses in such a circuit.

Bertus

#### zarabotkalesna

Joined Nov 22, 2015
18
And will I achieve the same goal if I use an Op-Amp instead of Common Base Amp?

#### bertus

Joined Apr 5, 2008
22,277
Hello,

For what do you want to use the created 15 Volts?
You can amplify 5 volts to 15 volts using an opamp, but you will need a powersupply to feed the opamp.

Bertus

#### zarabotkalesna

Joined Nov 22, 2015
18
Hello,

For what do you want to use the created 15 Volts?
You can amplify 5 volts to 15 volts using an opamp, but you will need a powersupply to feed the opamp.

Bertus
I have a bunch of CPU fans and I want to play with them

#### bertus

Joined Apr 5, 2008
22,277
Hello,

The power output of USB will be only 300 mA and 1 A when there is a request done.
This will likely be not enough to power the fans.

Bertus

#### zarabotkalesna

Joined Nov 22, 2015
18
I understand. Thank you all guys!!

#### ian field

Joined Oct 27, 2012
6,536
Doesn't look like a Common Base configuration to me. am I missing something?
Yes - the decoupling capacitor on the bottom of the base bias divider.