# I'm a noob trying to grasp the transistor concept - 2 questions

#### ClydeF

Joined Jun 10, 2018
8
Hey there,
I've just done some research into electronics for the first time because I want to create a circuit to make something.
I understand how transistors work but my question relates to how they turn on/off. I know that a voltage applied needs to be higher than a certain level for the switch to turn on (and if not it will be off), but I want to know..
'If you have a battery in a circuit with a transistor, how does the battery modulate the power output? (I assumed that it would always provide the same voltage to the transistor and not fluctuate)'
My second question is..
'When transistors are lined up in a H-bridge formation to convert DC current to AC, how can a single battery modulate which specific gates open? (So to ensure not to short circuit the circuit design)'

Thank you in advance to anyone that can answer my question. I really want to understand the concept.

-Clyde

#### HW-nut

Joined May 12, 2016
97

The battery output is constant. The circuit would be designed to produce the required modulation.

An H-bridge must be driven with the correct timing. Another circuit.

Take a look at the 555 ic for some ideas on timing.

Joined Mar 10, 2018
4,057

#### BR-549

Joined Sep 22, 2013
4,938
If you don't like textbooks and math.....I would suggest some power supplies, meters, signal generators, scope, breadboard and components. It's hard for a human to notice and clearly see fast things or events. Let alone the invisible electric and magnetic. Being able to see these changes in real time greatly helps understanding. One can adjust or vary circuit parameters while observing the effect. Think of it as animated math.

The internet is your most valuable tool. Hundreds of circuit, study and explanation examples for almost any application.

Then again.....are you asking how to turn a transistor on and off with a battery that is powering the transistor?

#### ebp

Joined Feb 8, 2018
2,332
What kind of transistors are you referring to - bipolar transistors or MOSFETs (Metal Oxide Semiconductor Field Effect Transistor)?

I don't really understand your first question. There are different ways to configure even a simple single transistor circuit. Can you post a schematic of the circuit you are wondering about? Something drawn by hand on paper and photographed is OK as long as we can see the necessary details.

#### ClydeF

Joined Jun 10, 2018
8
Thanks guys for the help!

What I'm trying to achieve is converting DC current from a battery to AC current which would power a 3V EL wire. I need AC power for this application but I don't want the lights to flash on/off; I want the lights to stay on consistently.
Would I be better off going down the path of a 'crystal oscillator', or the path of a 'H bridge circuit with a 555 ic timer'? I just need to know what to research next.

Cheers!

-Clyde

#### ClydeF

Joined Jun 10, 2018
8
@ebp basically I tried to draw my own circuit on paper but without enough appropriate knowledge.
It's basically 2x 3V coin batteries connected to some form of oscillator to convert Voltage from DC to AC. Then after that will be a small transformer that converts the 6V from the coin batteries into the 3V required for the EL wire.

#### AnalogKid

Joined Aug 1, 2013
9,479
Do you have a datasheet or link to other information about the EL wire?

ak

#### WBahn

Joined Mar 31, 2012
26,398
I doubt you are going to power those EL wires for very long with just two coin cells.

What you are looking for is basically an inverter. There are lots of them available off-the-shelf, though it might be hard finding one that isn't intended to output normal line voltage and power tens or hundreds of watts. Ones that are intended for your scale application probably exist, but they will likely tend to get lost in the power inverter noise.

How much current (RMS) does you EL wire require? What frequency? Can it be a squarewave instead of a sine wave?

#### ClydeF

Joined Jun 10, 2018
8
I doubt you are going to power those EL wires for very long with just two coin cells.

What you are looking for is basically an inverter. There are lots of them available off-the-shelf, though it might be hard finding one that isn't intended to output normal line voltage and power tens or hundreds of watts. Ones that are intended for your scale application probably exist, but they will likely tend to get lost in the power inverter noise.

How much current (RMS) does you EL wire require? What frequency? Can it be a squarewave instead of a sine wave?
Thanks for the reply. ^_^ It can be a square wave as far as I am aware and I'm looking to make the EL wire itself about 50cm long whilst being 1-2mm thick. It should draw around 5mA for the length of wire I want to power.
I want to make sure it is an AC current (I just need to know how to convert DC to AC with as small components as possible) and I want the light to be continuously 'ON' instead of flicking 'ON/OFF'.

Do you have a datasheet or link to other information about the EL wire?
There are many EL wires that are similar but ideally I am looking at one of the 3V options.

#### WBahn

Joined Mar 31, 2012
26,398
At that current, two logic gates should be able to drive it, particularly if it can tolerate 3.3 V. You just put the signal from a 555 astable multivibrator into two cascaded inverters (using a family that can both source and sink enough current) and put the EL wire between the two outputs.

#### BobTPH

Joined Jun 5, 2013
4,030
Please post a link to the 3V EL wire you have found. As far as I know, EL wire works at about 100 VAC.

Bob

#### ClydeF

Joined Jun 10, 2018
8
Sorry for skipping topics, I should probably start a new thread for the questions I want answered.
I’m slowly learning more basic things regarding what I’m wanting to do but I happened upon this link:
http://www.talkingelectronics.com/projects/Electroluminescence/LitELine04.html
It basically describes how to get flashing and continuous illumination but I only want continuous.
I have created a circuit on paper that I want reviewed because I still don’t really know some of the inner workings of how circuits operate. I assume the piece connected to the resistors on the left hand side of the circuit is a 555 ic. Here is a diagram below:

1. If the circuit would work as is?
2. If I need a transformer for any reason at all (e.g. voltage surge), while using a 3V coin battery for a 3V EL wire?
3. If I need a fly back diode for any reason at all? (Very small current flowing in this circuit)
4. Why these particular Resistors are used.

Thanks again in advance to anyone who can grant me a little more insight.

-Clyde

#### HW-nut

Joined May 12, 2016
97
No, the circuit will not work.
Yes, you need a transformer. The transformer provides the energy transfer/ voltage step up needed for the EL wire.
Yes, a diode (or snubber) is needed to prevent excessive voltage.
Need to finalize the circuit before doing the math.

#### Sensacell

Joined Jun 19, 2012
2,917
This circuit will not work, this circuit has no DC path.

Looking at the link you posted, the circuit drawn looks like an erroneous version, missing key parts.
The circuits on that page all show inductive components intended to boost voltage.

Electro-luminescent devices require high voltage AC to operate.
Standard "EL Wire" looks like a lossy capacitor electrically.
If your wire works on 3V, then it's not electro-luminescent, it's something else.

#### WBahn

Joined Mar 31, 2012
26,398
As has already been asked by others, please post a link to the information about the wire you are planning to use. At the very least, a manufacturer and part number.

#### ClydeF

Joined Jun 10, 2018
8
As has already been asked by others, please post a link to the information about the wire you are planning to use. At the very least, a manufacturer and part number.
Here’s one I have considered using ^_^:
https://www.littlebirdelectronics.com.au/high-brightness-blue-electroluminescent-el-wire-2

This circuit will not work, this circuit has no DC path.

Looking at the link you posted, the circuit drawn looks like an erroneous version, missing key parts.
The circuits on that page all show inductive components intended to boost voltage.

Electro-luminescent devices require high voltage AC to operate.
Standard "EL Wire" looks like a lossy capacitor electrically.
If your wire works on 3V, then it's not electro-luminescent, it's something else.
Ohk, I just assumed 3V would be the running power of the wire itself.

#### absf

Joined Dec 29, 2010
1,963

#### WBahn

Joined Mar 31, 2012
26,398

#### ClydeF

Joined Jun 10, 2018
8
No, the circuit will not work.
Yes, you need a transformer. The transformer provides the energy transfer/ voltage step up needed for the EL wire.
Yes, a diode (or snubber) is needed to prevent excessive voltage.
Need to finalize the circuit before doing the math.
So the circuit I drew is only missing the transformer which would change the battery voltage to the voltage required for the EL wire, as well as the flyback diode?

-Clyde