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ATtiny85: 5.5V max but what about overall power dissipation?
Posted on 5/1/20 at 12:16 pm
Posted on 5/1/20 at 12:16 pm
I have been using an LM555 chip and RC circuit, but an ATtiny85 can accomplish the same. However, it’s limited to 5.5V.
I’ve been running the 555 chip on a 7.5VDC 1A source (or 9V .5A) without issues.
I can easily find a 5-6VDC source, just wondering on power dissipation at the voltage to run my project.
I’ve been running the 555 chip on a 7.5VDC 1A source (or 9V .5A) without issues.
I can easily find a 5-6VDC source, just wondering on power dissipation at the voltage to run my project.
1
Posted on 5/1/20 at 2:14 pm to LSUAlum2001
So I am not sure I am following exactly. But you want to run a ATtiny85 micro for your project, but it's VCC input range is max 5.5V.
Obviously you do not want to supply with any VCC over 5.5V, more than likely you want to use 3.3V or 5V. I'm sure it will probably work if you bread board it straight to a DC wall wart, but that is not ideal.
Current requirements will be based on what you need to drive. I would select something that supplies twice the current you need. So if you expect peak current consumption to be 100mA then I would select something that is outputs either 3.3V or 5V with a minimum of 200mA.
Obviously you do not want to supply with any VCC over 5.5V, more than likely you want to use 3.3V or 5V. I'm sure it will probably work if you bread board it straight to a DC wall wart, but that is not ideal.
Current requirements will be based on what you need to drive. I would select something that supplies twice the current you need. So if you expect peak current consumption to be 100mA then I would select something that is outputs either 3.3V or 5V with a minimum of 200mA.
Posted on 5/1/20 at 2:45 pm to UltimaParadox
quote:
Obviously you do not want to supply with any VCC over 5.5V,
I know that.
Before I fry my output assembly (I've done it already
) I’d like to know how much the can ATt85 can be driven since everything is internal to it vs the 555 chip which needs the external components to make it work. .5A? Less? More?
Like I said previously, the current design can handle 7.5V at 1A or 9V at .5A.
At 5V, I have some 1A options, and I'm wondering if that can be used before frying components again. I guess I'll just have to purchase an arduino uno and some ATt85s to test out.
This post was edited on 5/1/20 at 3:52 pm
Posted on 5/1/20 at 4:49 pm to LSUAlum2001
quote:
I’d like to know how much the can ATt85 can be driven since everything is internal to it vs the 555 chip which needs the external components to make it work.
.5A? Less? More?
Your micro is only going to pull as much current as it needs. The current requirement will be based on your entire design. In simple terms, Frying components happens when you apply over voltage.
I would imagine a 5VDC power supply capable of supplying 1A would be perfectly fine. The ATt85 by itself is going to pull very little current. I mean sleep mode in the sub mA range and depending on the frequency maybe up to 20mA if you are not driving any external circuitry.
The external circuitry is what will drive your current requirements. Do you have a rough schematic?
This post was edited on 5/1/20 at 4:50 pm
Posted on 5/1/20 at 4:51 pm to LSUAlum2001
I’m not following What you’re asking.
What you need to do is grab the data sheet to understand what the chip will pull.
According to the datasheet, the chip pulls in the low ma range at 5v. Depends on the frequency. Know if you add loads on the outputs, it will pull even more. You don’t want more than 200ma powering the chip.
The outputs can’t drive more than 40ma, so If you need to drive more, you’ll need external components (which you’ll probably need anyway. If you want real help, y have to provide more information on what you are trying to accomplish.
What you need to do is grab the data sheet to understand what the chip will pull.
According to the datasheet, the chip pulls in the low ma range at 5v. Depends on the frequency. Know if you add loads on the outputs, it will pull even more. You don’t want more than 200ma powering the chip.
The outputs can’t drive more than 40ma, so If you need to drive more, you’ll need external components (which you’ll probably need anyway. If you want real help, y have to provide more information on what you are trying to accomplish.
Posted on 5/1/20 at 10:53 pm to UltimaParadox
quote:
The current requirement will be based on your entire design
It's driving a bank of LEDs through an LM555 chip. Initially I had it running on a 9V battery which can supply at least 200mA.
I decided to switch to an AC/DC adapter. I didn't realize (until after I purchased it) that I bought one with a 3A output. It was able to supply various voltages. It was putting out some serious heat. My device needs anywhere from 6-8V forward voltage to operate, depending on the LED configuration. Each leg was drawing 600mA using the 3A source and that was too much for the LEDs. A couple of configurations are drawing .2A and .1A per leg safely, depending upon the DC avail max current.
Since I'm limited to 5.5V with the ATt85 it may not work in some configurations, so I may look for other options.
This post was edited on 5/2/20 at 7:46 am
Posted on 5/2/20 at 7:57 am to LSUAlum2001
quote:
Each leg was drawing 600mA using the 3A source and that was too much for the LEDs
Maybe I am misunderstanding, but I think you are kind of approaching this backwards from the normal way.
You need to provide a resistor in series to limit the current drawn by the LED. The data sheet for the LED should provide you with current specs.
Sparkfun LED Current Limiting
Posted on 5/2/20 at 9:44 am to UltimaParadox
I did not want to add more components, especially one to limit radiance of the LEDs. I’m working on LED therapy devices and my goal was to find the maximum power dissipation it could handle. Higher output will penetrate deeper and be more effective.
I’ve found a good combination of 7.5V/1A and 9V/.5A that will maximize output while not over-driving the LEDs with 3x5 and 4x5 LED assemblies.
Back to the ATt85, the limitation of 5,5V is a problem, but I did buy a couple of them to test out and program using the uno.
Here is a sketch of the original design on the H&F Board and discussions on Red/Near IR LED therapy to reduce joint pain and inflammation.
LINK
I’ve found a good combination of 7.5V/1A and 9V/.5A that will maximize output while not over-driving the LEDs with 3x5 and 4x5 LED assemblies.
Back to the ATt85, the limitation of 5,5V is a problem, but I did buy a couple of them to test out and program using the uno.
Here is a sketch of the original design on the H&F Board and discussions on Red/Near IR LED therapy to reduce joint pain and inflammation.
LINK
This post was edited on 5/2/20 at 9:51 am
Posted on 5/2/20 at 1:20 pm to LSUAlum2001
Obviously I am not familiar with the application of the circuit so I do not understand the desired result..
That being said not having a current limit on your LED is not a good idea. LEDs are diodes and will not pull as much current as they need, and in simplistic terms will draw as much current as it can. This is bad will cause the LED to fail prematurely.
Your previous design was using an LM555 timer so probably cycling it on and off helped with limiting the amount of heat it had to dissipate.
Without knowing the part numbers of the LEDs you bought, this is my simplistic view of it. Some LEDs have built in resistors.
The best way to approach LEDs is to control the current instead of the voltage, that way you can maintain proper and constant brightness. Plus take a look at how forward voltage works in relative to forward current. Typically you will see that once a certain level of forward voltage is reached the current consumption goes up exponentially. This ramps up the heat for basically very little gain in the brightness.
That being said not having a current limit on your LED is not a good idea. LEDs are diodes and will not pull as much current as they need, and in simplistic terms will draw as much current as it can. This is bad will cause the LED to fail prematurely.
Your previous design was using an LM555 timer so probably cycling it on and off helped with limiting the amount of heat it had to dissipate.
Without knowing the part numbers of the LEDs you bought, this is my simplistic view of it. Some LEDs have built in resistors.
The best way to approach LEDs is to control the current instead of the voltage, that way you can maintain proper and constant brightness. Plus take a look at how forward voltage works in relative to forward current. Typically you will see that once a certain level of forward voltage is reached the current consumption goes up exponentially. This ramps up the heat for basically very little gain in the brightness.
Posted on 5/2/20 at 2:44 pm to UltimaParadox
Thanks for the help.
I have three or four different designs completed that are currently running and have been for several weeks. They put off almost no heat themselves to the skin, where it is directly applied. The only time I actually felt heat was during the 3A fiasco.
I should just pull out the oscope and check current levels. It’s hidden in a closet.
I’ll go back and look at my orders and check the spec sheets and data on the LEDs.
I have three or four different designs completed that are currently running and have been for several weeks. They put off almost no heat themselves to the skin, where it is directly applied. The only time I actually felt heat was during the 3A fiasco.
I should just pull out the oscope and check current levels. It’s hidden in a closet.
I’ll go back and look at my orders and check the spec sheets and data on the LEDs.
This post was edited on 5/2/20 at 2:48 pm
Posted on 5/2/20 at 3:48 pm to LSUAlum2001
Makes sense since it had a lot more current available to it.
Your application seems pretty neat. I am guessing moving from the timer to the ATtiny85 you are going to write the firmware to control the pulsing of the LEDs?
Let me know if you think I could help. All this shutdown stuff, been working at home all the time... got a bit more free time
Your application seems pretty neat. I am guessing moving from the timer to the ATtiny85 you are going to write the firmware to control the pulsing of the LEDs?
Let me know if you think I could help. All this shutdown stuff, been working at home all the time... got a bit more free time
Posted on 5/2/20 at 4:05 pm to UltimaParadox
Yes. I already have the code to pulse the LEDs.
I just don’t know if I’m going to get the desired result due to the 5.5V max which will limit the LED configurations.
I have an idea how to lay it out, it’ll just be more soldering.
I have a friend who has one of the 3x5 grid LED layouts for his plantar fascia issue and he has seen pain reduction. My knee is feeling much better after battling tendonosis for the last 3+ years. I went through a long Olympic lifting workout yesterday and the knee feels great.
I just don’t know if I’m going to get the desired result due to the 5.5V max which will limit the LED configurations.
I have an idea how to lay it out, it’ll just be more soldering.
I have a friend who has one of the 3x5 grid LED layouts for his plantar fascia issue and he has seen pain reduction. My knee is feeling much better after battling tendonosis for the last 3+ years. I went through a long Olympic lifting workout yesterday and the knee feels great.
This post was edited on 5/3/20 at 8:26 pm
Posted on 8/10/20 at 3:25 pm to LSUAlum2001
I just ordered some High Power LED emitters in 660nm (red) and 940nm (IR).
I should be able to create a design that is around 9W-14W, which will equal to 1W-1.5W for each LED output. This will push it near Class 4, but the LED divergence is wide. It'll still put out some heat, though, especially to the area you are treating.
I should be able to create a design that is around 9W-14W, which will equal to 1W-1.5W for each LED output. This will push it near Class 4, but the LED divergence is wide. It'll still put out some heat, though, especially to the area you are treating.
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