Passing High Voltage/Amperage Through Tri-State Buffer (car LED project)

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Discussion Overview

The discussion revolves around designing a circuit for controlling high-power LED applications using tri-state buffers and transistors. Participants explore the requirements for handling high voltage and current, the necessity of tri-state functionality, and the appropriate components for the task.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • Some participants inquire about the application context, specifically the need for high power (12V and up to 15A) and the role of tri-state buffers in the circuit.
  • One participant mentions using PWM current sink circuits to control LEDs efficiently, suggesting that logic operations should precede the final drive circuit.
  • Another participant expresses uncertainty about the required switching speeds and bandwidth, indicating a lack of experience in circuit design.
  • Several participants question the necessity of 12V for LEDs, suggesting that LEDs typically operate at lower voltages and asking for clarification on how the LEDs will be controlled (e.g., all at once, in groups, or with variable brightness).
  • Links to resources and selection guides for transistors and semiconductor components are shared to assist in the design process.
  • Participants emphasize the importance of providing detailed information and sketches to facilitate meaningful assistance in the design inquiry.

Areas of Agreement / Disagreement

There is no consensus on the best approach to control the LEDs, as participants express differing views on the voltage requirements and control methods. The discussion remains unresolved regarding the optimal components and strategies for the circuit design.

Contextual Notes

Participants note limitations in the initial queries, such as the lack of specific details about the control strategy for the LEDs and the necessity of high current ratings for the transistors. The discussion also reflects varying levels of experience among participants, which may influence the depth of technical understanding.

Who May Find This Useful

This discussion may be useful for electronics enthusiasts, particularly those interested in automotive LED applications, circuit design involving tri-state buffers and transistors, and those seeking guidance on handling high power in electronic circuits.

Hebrew Hammer
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Hi guys,

I'm a total greenhorn so please bear with me. I'm designing a circuit in which I use a lot of tri-state buffers. All ICs in the circuit will be powered with 5V, but I need to pass 12V (and up to 15A) from the input to the output of the tri-state buffers when the buffer is enabled. Are there buffers I can use that can handle this type of power?
 
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Hebrew Hammer said:
Hi guys,

I'm a total greenhorn so please bear with me. I'm designing a circuit in which I use a lot of tri-state buffers. All ICs in the circuit will be powered with 5V, but I need to pass 12V (and up to 15A) from the input to the output of the tri-state buffers when the buffer is enabled. Are there buffers I can use that can handle this type of power?

Welcome to the PF.

Can you tell us a bit about the application? Why so much power? And why the need for the Tri-State feature? What switching speeds for the propagation delay through the buffers as the state changes Low-High-Low? What bandwidth are the digital signals you are sending through the buffers?

In the end it may be best to use Analog Switches, but we'll need to know more first...
 
berkeman said:
Welcome to the PF.

Can you tell us a bit about the application? Why so much power? And why the need for the Tri-State feature? What switching speeds for the propagation delay through the buffers as the state changes Low-High-Low? What bandwidth are the digital signals you are sending through the buffers?

In the end it may be best to use Analog Switches, but we'll need to know more first...

Basically what I'm making is a controller for LED's (in an automotive application) and it has to be able to power a lot of them! I selected tri-state buffers as a way to connect multiple inputs to the same output and select which input is used based on input to the device. I'm really not sure what I need for switching speeds, I probably don't need anything particularly fast. I've never designed anything like this before and a lot of this is completely new to me. I'm learning as I go. In terms of signal bandwidth, only one bit will be passing through any buffer at any given time. That is what you mean by bandwidth, correct? I hope I answered your questions adequately, I appreciate the help!
 
Hebrew Hammer said:
Basically what I'm making is a controller for LED's (in an automotive application) and it has to be able to power a lot of them! I selected tri-state buffers as a way to connect multiple inputs to the same output and select which input is used based on input to the device. I'm really not sure what I need for switching speeds, I probably don't need anything particularly fast. I've never designed anything like this before and a lot of this is completely new to me. I'm learning as I go. In terms of signal bandwidth, only one bit will be passing through any buffer at any given time. That is what you mean by bandwidth, correct? I hope I answered your questions adequately, I appreciate the help!

Thanks, that helps. So you have an LED drive application that will involve moderate power. Have you done much reading yet about LED lighting and controllers? To save power, you would control the LEDs typically with PWM current sink circuits. You would do your logic stuff before the final drive circuit, and control the PWM signal for each string of LEDs using the final logic information.

Can you say how many LEDs you want to control, and in what kind of groups?
 
I basically need to control four distinct groups of LEDs. I'm including a link to the spec sheet for the LEDs I'm using. I'd like to control between 600 and 900 LEDs. I honestly don't know anything about PWM current sink circuits so I will begin researching!
http://www.oraclelights.com/Images/Interior/specsheets/oracle_lighting_flex_5050_spec_sheet.jpg
 
I'm building a digital device for controlling LEDs. I need some help figuring out the correct transistor for switching use. The control circuit will run on 5V (and that will be the voltage applied at the transistor base when current is to flow through) and the transistor will have to be able to pass 12V and up to 15 or 20A from the collector to the emitter. I haven't worked with transistors before (I'm an electronics greenhorn) so any and all help is appreciated!
 
Hebrew Hammer said:
I'm building a digital device for controlling LEDs. I need some help figuring out the correct transistor for switching use. The control circuit will run on 5V (and that will be the voltage applied at the transistor base when current is to flow through) and the transistor will have to be able to pass 12V and up to 15 or 20A from the collector to the emitter. I haven't worked with transistors before (I'm an electronics greenhorn) so any and all help is appreciated!
How many LEDs are you controlling that you would need 15 to 20 amps ? And why 12V? LEDs activate on much lower voltages.
 
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That is the typical first response! Ideally I want to be able to control about 1,000 LEDs. This control unit will be used for automotive applications and so the LEDs being used (having also been set up for automotive use) are run at 12V.
 
  • #10
It's meaningless to say "I want to control 1000 12v LED's and need a transistor".

You want to control them how? Turn them all on at once? Turn 1 at a time? Groups of 100? Flash? Variable brightness with PWM?

Also, Post a link to the LED spec sheet. Why do people think we are telepathic?

If you really want meaningful help, post a sketch of what you are trying to do. Show you have thought about it a bit.
 
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  • #11
Hebrew Hammer said:
That is the typical first response! Ideally I want to be able to control about 1,000 LEDs. This control unit will be used for automotive applications and so the LEDs being used (having also been set up for automotive use) are run at 12V.
OK, makes sense on both counts although your statement that the LEDS "run on 12V" does NOT sound correct ... what you mean, I assume, is that the LEDS have to operate in a circuit with a 12v source.

I second BigGuy's suggestion that you think we are telepathic.
 
  • #12
Hebrew Hammer said:
That is the typical first response!

i trust that wasn't condescension..

anyhow - all semiconductor manufacturers provide selection guides

search on "parametric transistor selection guide"

my first two hits:
http://www.onsemi.com/PowerSolutions/taxonomy.do?id=797
http://www.ti.com/analog/docs/analogtechdoc_hh.tsp?viewType=mostrecent&rootFamilyId=64&familyId=1941&docCategoryId=10
 
  • #13
<< Two threads on same subject merged... >>[/color]
 
  • #14
jim hardy said:
i trust that wasn't condescension..

anyhow - all semiconductor manufacturers provide selection guides

search on "parametric transistor selection guide"

my first two hits:
http://www.onsemi.com/PowerSolutions/taxonomy.do?id=797
http://www.ti.com/analog/docs/analogtechdoc_hh.tsp?viewType=mostrecent&rootFamilyId=64&familyId=1941&docCategoryId=10

You trust correctly, phinds asked the logical first question. Thank you for the links, the first one looks particularly helpful. I'm going to spend some time going through it.

meBigGuy said:
It's meaningless to say "I want to control 1000 12v LED's and need a transistor".

You want to control them how? Turn them all on at once? Turn 1 at a time? Groups of 100? Flash? Variable brightness with PWM?

Also, Post a link to the LED spec sheet. Why do people think we are telepathic?

If you really want meaningful help, post a sketch of what you are trying to do. Show you have thought about it a bit.

This is a link to the data sheet for the LEDs: http://www.oraclelights.com/Images/Interior/specsheets/oracle_lighting_flex_5050_spec_sheet.jpg

What I said, although it wasn't particularly specific, was that it will be used for switching. Basically I just need it to turn all of them on and off.

phinds said:
OK, makes sense on both counts although your statement that the LEDS "run on 12V" does NOT sound correct ... what you mean, I assume, is that the LEDS have to operate in a circuit with a 12v source.

I second BigGuy's suggestion that you think we are telepathic.

You are correct about the voltage.

I appreciate the help and patience, I've taken on a bit of an ambitious first electronics project!
 
  • #15
Hebrew Hammer said:
You trust correctly, phinds asked the logical first question.
Yeah, I took it as being something like "yeah, that's what everyone says 'til I explain it more"
I appreciate the help and patience, I've taken on a bit of an ambitious first electronics project!
Shouldn't be too hard ... big thing is to find the right power transistor and in case you are not aware of them, might want to read up on transistor heat sinks.
 
  • #16
The spec sheet tells very little about what is actually on the strips. There are "bridgelux 5050 RGB" LEDs used in the RGB strips, but there are no specs for a 5050 RGB at bridgelux, and there are many different possible varieties other than RGB listed at the bottom of the sheet.

As for bridgelux, there is no spec for a 5050RGB, no results for 5050, and no pertinent results for RGB.
http://www.bridgelux.com/products/led-chips/
They are sold binned for voltage, so I expect they are parallel on the strip?, and there is no resistor?. But, I am not at all sure.
I looked at 1 Blue power chip and it was rated for brightness at 350ma (3.4V forward voltage)
http://www.bridgelux.com/wp-content/uploads/2013/10/BXCD4545-45mil-x-45mil-or-1.14mm-x-1.14mm-Datasheet-DS-C15.pdf

300 LED's per strip on the spec sheet at the link provided.
 
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  • #17
phinds said:
Yeah, I took it as being something like "yeah, that's what everyone says 'til I explain it more"

Shouldn't be too hard ... big thing is to find the right power transistor and in case you are not aware of them, might want to read up on transistor heat sinks.

I apologize, one of the downsides of typed communications unfortunately. I'll look into heat sinks. Once I think I've found the right transistor I will post it up!

meBigGuy said:
The spec sheet tells very little about what is actually on the strips. There are "bridgelux 5050 RGB" LEDs used in the RGB strips, but there are no specs for a 5050 RGB at bridgelux, and there are many different possible varieties other than RGB listed at the bottom of the sheet.

As for bridgelux, there is no spec for a 5050RGB, no results for 5050, and no pertinent results for RGB.
http://www.bridgelux.com/products/led-chips/
They are sold binned for voltage, so I expect they are parallel on the strip?, and there is no resistor?. But, I am not at all sure.
I looked at 1 Blue power chip and it was rated for brightness at 350ma (3.4V forward voltage)
http://www.bridgelux.com/wp-content/uploads/2013/10/BXCD4545-45mil-x-45mil-or-1.14mm-x-1.14mm-Datasheet-DS-C15.pdf

300 LED's per strip on the spec sheet at the link provided.

I agree that the spec sheet isn't very informative. I believe that the LEDs are parallel in groups of three on the strip (which seems to make sense given the forward voltage on that Blue chip). I also don't think there is any resistor in the strip.
 
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  • #18
Hebrew Hammer said:
I also don't think there is any resistor in the strip.

since they tell us to connect to a 12V 10% 'class 2' supply, it's a fairly safe bet there's something on the strip to set current. Could be an active current controller or a simple resistor... Will they sample you one to examine ?

i looked up 'class 2 supply' and it means, per US NEC, current limited to lesser of 100VA or 5 amps...

interesting project.

old jim
 
  • #19
jim hardy said:
since they tell us to connect to a 12V 10% 'class 2' supply, it's a fairly safe bet there's something on the strip to set current. Could be an active current controller or a simple resistor... Will they sample you one to examine ?

i looked up 'class 2 supply' and it means, per US NEC, current limited to lesser of 100VA or 5 amps...

interesting project.

old jim

If there is something on the strip it has to be a resistor. I am supposed to be getting a sample in the mail some time soon.

Does anyone have a good resource where I can read up and really get a good grasp on transistors, (types, selection, etc.)?

What I have right now is this:

My control signal to the base of the transistor will be 5V and 5mA. The load will be 12V and up to (ideally) 20A. It is my current impression that I should use an NPN transistor, but I'm struggling to find the correct transistors for my project. I have never worked with transistors so I thought finding a good educational resource might be a good move.
 

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