# increasing voltage or current

#### kourosh daryaee

May 12, 2016
38
hello there
i have a little circuit with a mono input jack and power input.it gets the sound from from audio jack and according to level of it sound the LED's (10 LED ) on the board will switch on.
now i wanted to increase number of LED's from 10 to 60, so i packed the LED's in groups of 6 paralleled LED to connect each of these pack to one of the LED's on the board , but the limit of voltage or current wont let LED's to work.
i have time and a little of passion on electronic so there's no problem if solution will be complicated.
now i have some question :
1 : since i paralleled these LED's ,should i increase current or voltage?how much?
2 : how can i do that in a way that every time one of the LED's on the board turns on one of my LED packs (6 LED's) turns on?

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#### Alec_t

Jul 7, 2015
3,356
Welcome to EP!
Connecting six LEDs in series would be preferable to connecting them in parallel.
What is the supply voltage of your circuit?
Do you have any other supplies available?
What colour are the LEDs?

#### kourosh daryaee

May 12, 2016
38
i already soldered them parallel, so if you can see it that way
the circuit works in 6 to 12 volts
yea i can add other supplies to it
the 60 led are on different colors for example blue, red,green,white,orange
it would be great if it can work with something like car battery (12v)

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#### Alec_t

Jul 7, 2015
3,356
LEDs have a forward voltage (Vf) which depends on the colour. Typical Vf voltages are e.g. 1.8V for a red LED, 2.1V for a green, 3.1V for a white. By connecting different colours in parallel the lowest Vf will dominate and effectively 'short out' the other colours. So you would expect significant brightness from the red LEDs only. You may be lucky and the other colours may light dimly.

#### Herschel Peeler

Feb 21, 2016
401
hello there
i have a little circuit with a mono input jack and power input.it gets the sound from from audio jack and according to level of it sound the LED's (10 LED ) on the board will switch on.
now i wanted to increase number of LED's from 10 to 60, so i packed the LED's in groups of 6 paralleled LED to connect each of these pack to one of the LED's on the board , but the limit of voltage or current wont let LED's to work.
i have time and a little of passion on electronic so there's no problem if solution will be complicated.
now i have some question :
1 : since i paralleled these LED's ,should i increase current or voltage?how much?
2 : how can i do that in a way that every time one of the LED's on the board turns on one of my LED packs (6 LED's) turns on?

6 LEDs in parallel means 6 times the current.

#### kourosh daryaee

May 12, 2016
38
thanks for your information and instruction ,it was great.
i tested them with 2 batteries serried and their light wasn't that bad.
but what about how to connect them to the led on the board?
since the board have 10 LED's and i want to connect each pack of six LED to one of them

#### Gryd3

Jun 25, 2014
4,098
i already soldered them parallel, so if you can see it that way
the circuit works in 6 to 12 volts
yea i can add other supplies to it
the 60 led are on different colors for example blue, red,green,white,orange
it would be great if it can work with something like car battery (12v)
Time to break out the soldering iron again.
LEDs in parallel are almost always a bad idea.
If this is the way you really want it to be parallel, you should put a resistor on each one *before* you connect them in parallel.
In any case, you end up with a collection of LEDs that won't work properly, or that waste excessive power.

Do yourself a huge favour and make a few 'groups' by soldering 3-4 in series with a resistor. You can then join the groups together in parallel. This would be ideal, will ensure consistent light, be more effecient, and protect the LEDs.

#### kourosh daryaee

May 12, 2016
38
thanks again , sounds like i did a big mistake.since i glued them to platform its not possible to change it.
but take look at this picture please ,i already soldered and glued them parallel to the platform ,so if you can help me with the problem i have with syncing and powering these LED's in the same time that would be great for now.

#### Gryd3

Jun 25, 2014
4,098
thanks again , sounds like i did a big mistake.since i glued them to platform its not possible to change it.
but take look at this picture please ,i already soldered and glued them parallel to the platform ,so if you can help me with the problem i have with syncing and powering these LED's in the same time that would be great for now.
Unfortunately, there is no method you can currently employ with that circuit...
If you have two different types of LEDs in parallel, the lower Vf rated LED with light first. The higher one may not light at all, or may be very dim. Increasing the applied voltage will merely increase the current through the lower Vf LEDs resulting in damage to the LED... once it fails, the higher Vf LED will then light up
You may be able to salvage it by carefully removing the glue from some of the wires/contacts. Considering what was done... you may have to settle for one resistor on each LED... (or at least one resistor for each 'color' of LED). If you can manage to separate one terminal or the other of the LED, you can insert a resistor inbetween.
This will draw a lot of current and is not *ideal* but is still very functional and will protect and power each LED properly.

#### kourosh daryaee

May 12, 2016
38
Unfortunately, there is no method you can currently employ with that circuit...
If you have two different types of LEDs in parallel, the lower Vf rated LED with light first. The higher one may not light at all, or may be very dim. Increasing the applied voltage will merely increase the current through the lower Vf LEDs resulting in damage to the LED... once it fails, the higher Vf LED will then light up
You may be able to salvage it by carefully removing the glue from some of the wires/contacts. Considering what was done... you may have to settle for one resistor on each LED... (or at least one resistor for each 'color' of LED). If you can manage to separate one terminal or the other of the LED, you can insert a resistor inbetween.
This will draw a lot of current and is not *ideal* but is still very functional and will protect and power each LED properly.

Thank you , that was a great help
when i done that ,how can i sync these LED's with the one on the board?

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#### Gryd3

Jun 25, 2014
4,098
Thank you , that was a great help
Good luck..
If I recall.. you wanted it to work on 12V .
Remember that the colours will drop a varying voltage from 1.8 to 3.1V (depending on colour of course)
This means that your resistor will need to drop 8.9V - 10.2V .. at most likely 20mA.
You will need 470Ω and 510Ω resistors... but the concern we had with efficiency means that these resistors will need to handle up to 1/4W and will get quite warm. 1/2W will be safer, but also much larger.
You cannot use surface mount resistors, even though their tiny size would make this repair much easier.

The only solution here is to use a lower voltage to power the LEDs.
Any method you use will need to supply at least 1.2Amps . Keep us posted and we can help along the way.

#### BobK

Jan 5, 2010
7,682
There are two issues here.

First is how to connect 6 LEDs efficiently. This is done with series and parallel as Gryd3 suggested.

There there is the issue of driving them from the board.

Let's assume you end up with two strings of 3 LEDs to put in parallel with each for each of the 10 separate LEDs on the board. This will be an additional 40mA needed to drive them. The chip on the board might be able to do this, or it might not. Most probably not. So you need a transistor switch connected to each of the 10 positions on the board that will then drive the 2 strings of 3 LEDs.

Bob

#### kourosh daryaee

May 12, 2016
38
There are two issues here.

First is how to connect 6 LEDs efficiently. This is done with series and parallel as Gryd3 suggested.

There there is the issue of driving them from the board.

Let's assume you end up with two strings of 3 LEDs to put in parallel with each for each of the 10 separate LEDs on the board. This will be an additional 40mA needed to drive them. The chip on the board might be able to do this, or it might not. Most probably not. So you need a transistor switch connected to each of the 10 positions on the board that will then drive the 2 strings of 3 LEDs.

Bob
Thank you Bob
Can you be a bit more specific about what transistor to use ?
and is it possible to use additional 90mA for each group of 6 so i can keep the form of platform?

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Moderator
Nov 17, 2011
13,194

May 12, 2016
38

#### kourosh daryaee

May 12, 2016
38

There's a new problem . the switch current in the circuit that i have is the current on the red diode
and from what i learned from this article its something like 15ma but the hfe (minimum gain they need to switch on?) of the transistors i found on the article that bob send is 50(ma?) on datasheet.
so am i right about the hfe(as the minimum gain)? and where i can find a transistor that has a minimum gain of 15ma ,Iload of 200ma and V of 1.8v and it need to be able to handle a voltage and current of car battery which is 12v and i don't know the current of it.
If i have a transistor for load of 300ma and 4v for example and i give it 12v as the load what happens?will it blow ? or it will pass the 4v?
sound like i am asking for the whole of electronic circuit knowledge here. thanks for you patience.

Thank you
Kourosh

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#### Gryd3

Jun 25, 2014
4,098
There's a new problem . the switch current in the circuit that i have is the current on the red diode
and from what i learned from this article its something like 15ma but the hfe (minimum gain they need to switch on?) of the transistors i found on the article that bob send is 50(ma?) on datasheet.
so am i right about the hfe(as the minimum gain)? and where i can find a transistor that has a minimum gain of 15ma ,Iload of 200ma and V of 1.8v and it need to be able to handle a voltage and current of car battery which is 12v and i don't know the current of it.
If i have a transistor for load of 300ma and 4v for example and i give it 12v as the load what happens?will it blow ? or it will pass the 4v?
sound like i am asking for the whole of electronic circuit knowledge here. thanks for you patience.

Thanks you
Kourosh
I can't answer the transistor question right away, but I encourage you to stop thinking about the 'capabilities' of the car battery as something you need to control.
Have you ever replaced a 120W light bulb with a 60W, fluorescent or LED bulb in your home?
In a car battery and in your home. The *source* provides voltage. The device connected to the source will *pull* whatever current is required to run itself. (As long as it's operating on the proper voltage)
So although a car battery can put our over 100A, you can still hook up a transistor and a string of LEDs that only takes 20mA-50mA. The components you use only need to handle 12V, and a little more than what you're device *draws*.
In one of my past posts, I stated that your parallel LEDs may draw at least 1.2Amps if they are ALL wired in parallel. If this is the case, you need a transistor to either handle all the LEDs at the same time... or multiple smaller transistors that handle sections of LEDs instead.

#### BobK

Jan 5, 2010
7,682
There's a new problem . the switch current in the circuit that i have is the current on the red diode
and from what i learned from this article its something like 15ma but the hfe (minimum gain they need to switch on?) of the transistors i found on the article that bob send is 50(ma?) on datasheet.
so am i right about the hfe(as the minimum gain)? and where i can find a transistor that has a minimum gain of 15ma ,Iload of 200ma and V of 1.8v and it need to be able to handle a voltage and current of car battery which is 12v and i don't know the current of it.
If i have a transistor for load of 300ma and 4v for example and i give it 12v as the load what happens?will it blow ? or it will pass the 4v?
sound like i am asking for the whole of electronic circuit knowledge here. thanks for you patience.

Thank you
Kourosh
You are very confused about the meaning of Hfe. First of all, it is a pure number, not something measured in mA.

The gain of a transistor is the ratio of the collector current to the base current under certain conditions. And it changes under other conditions.

If you need 15mA of collector current and the gain of the transistor is 50, you will need 15/50 = 0.3mA of base current.

In relation to your problem, the board you are using has LEDs on it and a chip driving them. That chip is able to provide the current for the LED on board, but probably not for the 6 more LEDs that you want to energize. This where the transistor comes in. If the transistor has a gain of 100, you need to draw only 1/100th of the current needed for the LEDs from your board and run it into the base of the transistor. Then, the full current comes through the collector.

The other reason for using the transistor is that you can use a higher voltage, and put more LEDs in series. The voltage across the LEDs on the board will be something lilke 2V. But this 2V can be applied to the base of the transistor, through a resistor to limit the current, and switch on 12V to run your strings of LEDs.

Bob

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