DIWdiver
Flashlight Enthusiast
Re: Adjustable 10A linear constant current driver
Got it. I can ship those on Monday.
Thanks!
Got it. I can ship those on Monday.
Thanks!
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Sold/Expired Adjustable 10A linear LED driver - New and Improved!
- Thread starter DIWdiver
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DIWdiver
Flashlight Enthusiast
Re: Adjustable 10A linear constant current driver
Got your payment. I have those in stock, so will ship tomorrow. Thanks!
Got your payment. I have those in stock, so will ship tomorrow. Thanks!
Re: Adjustable 10A linear constant current driver
General question about the schematic.
Some of the resistor values don't seem to be labeled. I guess the 6 on the end is confusing. For example, is R3 a 36K or a 3K ohm resistor?
R1 R3 R2 R8
0R05 3K6 3M6 3K6
Also, R8 shows no connection. From where R8 is placed on the schematic it looks like maybe it is connected between the (-) terminal on the op amp and in between the source of the FET and R1 but I'm not sure.
General question about the operation. (just curious how it works)
It looks like the switch connections H, L, & C setup a a voltage divider which determines the amount of voltage applied to the (+) terminal on the op amp. The H-C connection gives a higher input voltage than the L-C connection. I'm not sure what the specific configuration of the op amp is and how to relate input to output voltage but I'm assuming it's not setup to rail one way or the other (like a comparator) but rather the higher input voltage the higher output voltage? This would in turn determine the amount of voltage applied to the gate of the FET and change the amount of drain to source current. I've seen similar type circuits before and have always been confused as to how they work. I'm not sure if the resistance of the FET is changing signifigantly enough to vary the current or if something else is happening.
Regardless of my limited understanding... cool design :thumbsup: and I'm getting excited about setting up my SBT-90 build with one of these drivers.
General question about the schematic.
Some of the resistor values don't seem to be labeled. I guess the 6 on the end is confusing. For example, is R3 a 36K or a 3K ohm resistor?
R1 R3 R2 R8
0R05 3K6 3M6 3K6
Also, R8 shows no connection. From where R8 is placed on the schematic it looks like maybe it is connected between the (-) terminal on the op amp and in between the source of the FET and R1 but I'm not sure.
General question about the operation. (just curious how it works)
It looks like the switch connections H, L, & C setup a a voltage divider which determines the amount of voltage applied to the (+) terminal on the op amp. The H-C connection gives a higher input voltage than the L-C connection. I'm not sure what the specific configuration of the op amp is and how to relate input to output voltage but I'm assuming it's not setup to rail one way or the other (like a comparator) but rather the higher input voltage the higher output voltage? This would in turn determine the amount of voltage applied to the gate of the FET and change the amount of drain to source current. I've seen similar type circuits before and have always been confused as to how they work. I'm not sure if the resistance of the FET is changing signifigantly enough to vary the current or if something else is happening.
Regardless of my limited understanding... cool design :thumbsup: and I'm getting excited about setting up my SBT-90 build with one of these drivers.
DIWdiver
Flashlight Enthusiast
Re: Adjustable 10A linear constant current driver
You seem to understand fairly well so far.
Since decimal points are easy to loose or miss, we often use the convention of replacing it with a multiplier, thus 3.6K becomes 3K6, and 0.005 ohms becomes 0R005, or R005.
One way to think of a FET is as a voltage-controlled resistor. When the FET is 'on' the resistance is very low. This resistance is one of the primary specs of the FET. When it's 'off' the resistance is very high. Many applications use the FET in only 'on' and 'off' conditions. But there is a region between on and off where the resistance changes with gate voltage. This circuit uses the FET in that region. And yes, the resistance changes a lot (many orders of magnitude).
The op-amp and FET are set up as a constant current sink. The current flow through R1 is the same as that through the FET, and more importantly, the same as the LED. The voltage developed across R1 is compared to the reference voltage from the divider circuit. If it's lower, the op-amp increases the voltage on the gate of the FET, thus causing it to conduct more current. If the voltage is higher than the reference, the op-amp reduces the gate voltage, thus reducing the current. Since the gain of the op-amp is very high, only a tiny change in sense voltage (across R1) is needed to cause a large change in gate voltage on the FET. Thus the sense voltage is always kept very close to the reference voltage, which means the LED current is kept constant, no matter what the conditions. It only changes when the reference voltage changes. Variations in input voltage, temperature, and between individual parts cause the gate voltage requirements to change, but the LED current is practically independent of these fluctuations. It depends only on the value of R1 and the reference voltage. These can be kept pretty constant.
If you're wondering what R2 is for, it provides a little negative offset. The op-amp has a small and unpredictable offset between the two inputs. If I didn't correct for this, it's possible that there would still be some current in the LED even when the reference voltage is taken to zero (which should turn the LED off). R2 overcomes the offset in the op-amp and guarantees that the output will be zero when the reference voltage is zero.
C1 and R8 reduce the bandwidth of the circuit, to prevent it from oscillating.
You seem to understand fairly well so far.
Since decimal points are easy to loose or miss, we often use the convention of replacing it with a multiplier, thus 3.6K becomes 3K6, and 0.005 ohms becomes 0R005, or R005.
One way to think of a FET is as a voltage-controlled resistor. When the FET is 'on' the resistance is very low. This resistance is one of the primary specs of the FET. When it's 'off' the resistance is very high. Many applications use the FET in only 'on' and 'off' conditions. But there is a region between on and off where the resistance changes with gate voltage. This circuit uses the FET in that region. And yes, the resistance changes a lot (many orders of magnitude).
The op-amp and FET are set up as a constant current sink. The current flow through R1 is the same as that through the FET, and more importantly, the same as the LED. The voltage developed across R1 is compared to the reference voltage from the divider circuit. If it's lower, the op-amp increases the voltage on the gate of the FET, thus causing it to conduct more current. If the voltage is higher than the reference, the op-amp reduces the gate voltage, thus reducing the current. Since the gain of the op-amp is very high, only a tiny change in sense voltage (across R1) is needed to cause a large change in gate voltage on the FET. Thus the sense voltage is always kept very close to the reference voltage, which means the LED current is kept constant, no matter what the conditions. It only changes when the reference voltage changes. Variations in input voltage, temperature, and between individual parts cause the gate voltage requirements to change, but the LED current is practically independent of these fluctuations. It depends only on the value of R1 and the reference voltage. These can be kept pretty constant.
If you're wondering what R2 is for, it provides a little negative offset. The op-amp has a small and unpredictable offset between the two inputs. If I didn't correct for this, it's possible that there would still be some current in the LED even when the reference voltage is taken to zero (which should turn the LED off). R2 overcomes the offset in the op-amp and guarantees that the output will be zero when the reference voltage is zero.
C1 and R8 reduce the bandwidth of the circuit, to prevent it from oscillating.
Re: Adjustable 10A linear constant current driver
Pretty cool. Thanks for the detailed explanation! I understand now how the constant current portion works. That works out nice how the op amp takes care of where the FET is operating and all you have to worry about is the reference voltage, size of R1 and what you want the current to be.
Pretty cool. Thanks for the detailed explanation! I understand now how the constant current portion works. That works out nice how the op amp takes care of where the FET is operating and all you have to worry about is the reference voltage, size of R1 and what you want the current to be.
jwhughes1115
Newly Enlightened
- Joined
- Jan 16, 2012
- Messages
- 3
DIW,
I'd like 2xis1006-512. $54.95. Is that correct? Thanks.
-1115
-1115
DIWdiver
Flashlight Enthusiast
Actually, shipping is now $5.15, so the total is $55.15.
Sorry for the delay, I had somehow missed that there was an update in the thread.
DIWdiver
Flashlight Enthusiast
What's a pt54? I did a search at Luminus.com and came up with two obscure references that didn't tell me anything useful.
I would guess that 'positive grounding' means that the + terminal of the LED is connected to the metal substrate of the module. Is that correct?
In any event the answer is yes, it will work, if you properly isolate the necessary parts. The driver works with the + terminal of the LED connected to the + terminal of the battery (B+ and L+ are connected at the driver), but the - terminal of the LED which connects to L- on the driver, must not be connected to anything else. The thermal tab of the driver is connected to this terminal as well, so in most cases you have to electrically isolate the thermal tab from the heatsink. This only becomes unnecessary if the heatsink is not connected to anything else in the circuit (which is pretty unusual in flashlights).
DIWdiver
Flashlight Enthusiast
Yes, it will work. The only question is how much of a heat problem will you have. The driver has a minimum input voltage of 3.2V, so you can't go really close to the emitter voltage. But a single Li-ion cell should work, or 3 NiMH in series, and the heat problems would be managable.
DIWdiver
Flashlight Enthusiast
I could get the input voltage as low as 2.7V with only a minimal re-design (new parts, not new boards). That would be a $10 customization fee since you are looking at more than a current setting change (which would be $5).
Keep in mind that the driver has a 0.25-0.30V dropout voltage (input voltage must be 0.25-0.30V higher than output voltage to achieve full power). This could be reduced to around 0.15V in a full custom design at slightly higher cost.
wannabe333
Newly Enlightened
- Joined
- Apr 10, 2012
- Messages
- 70
Re: Adjustable 10A linear constant current driver
Hello DIW,
to keep the thread alive, here is what i want : 2
IS1006-1025 10 2.5
is there datasheeto to come with it?
Hello DIW,
to keep the thread alive, here is what i want : 2
IS1006-1025 10 2.5
is there datasheeto to come with it?
DIWdiver
Flashlight Enthusiast
Re: Adjustable 10A linear constant current driver
There's a data sheet, but I don't include a hard copy. I can e-mail it to you now if you like. Just post or PM me your e-mail address.
There's a data sheet, but I don't include a hard copy. I can e-mail it to you now if you like. Just post or PM me your e-mail address.
Kenom
Enlightened
Re: Adjustable 10A linear constant current driver
Am I correct in assuming that these would work well for driving a SST-90 via automotive application? I'm looking to utilize this as a driver for some driving lights on my motorcycle. Obviously I would need the input voltage capable of handling more than 12V. I love the dual output with switch option as I can choose to go high/low for in town and on highway.
Am I correct in assuming that these would work well for driving a SST-90 via automotive application? I'm looking to utilize this as a driver for some driving lights on my motorcycle. Obviously I would need the input voltage capable of handling more than 12V. I love the dual output with switch option as I can choose to go high/low for in town and on highway.
DIWdiver
Flashlight Enthusiast
Re: Adjustable 10A linear constant current driver
Several people in the automotive forum are using it already, or at least building with it. I replaced a few parts and added some external protection components for them.
There seemed to be enough interest that I actually designed a special board just for automotive use. I'll be building the first prototype tomorrow. It will have better protection from the nasty automotive electrical environment, better power-handling, and some thermal protection as well. If all goes well it will be available for sale in the next few weeks. Of course it could be much longer than that if something DOESN"T go smoothly.
You may also want to check out the automotive forum for discussions of legal issues around making your own vehicle lights. The guys I've sold to are all planning on using them off-road only.
Either the IS1006 or the IS1011 would be suitable, but they will both have serious thermal issues unless you run three LEDs in series. It's been discussed ad nauseum previously, read back if you're interested in the details. There are other drivers that might be better for a single LED.
Several people in the automotive forum are using it already, or at least building with it. I replaced a few parts and added some external protection components for them.
There seemed to be enough interest that I actually designed a special board just for automotive use. I'll be building the first prototype tomorrow. It will have better protection from the nasty automotive electrical environment, better power-handling, and some thermal protection as well. If all goes well it will be available for sale in the next few weeks. Of course it could be much longer than that if something DOESN"T go smoothly.
You may also want to check out the automotive forum for discussions of legal issues around making your own vehicle lights. The guys I've sold to are all planning on using them off-road only.
Either the IS1006 or the IS1011 would be suitable, but they will both have serious thermal issues unless you run three LEDs in series. It's been discussed ad nauseum previously, read back if you're interested in the details. There are other drivers that might be better for a single LED.
Kenom
Enlightened
Re: Adjustable 10A linear constant current driver
I'm not concerned about legal issues. They will essentially be "fog lights" and there is nothing illegal about using them on the roads as long as they are not in folks's eyes.
I'm not concerned about thermal protection either as the driver will be mounted on the opposite side of this heatsink:
http://www.mouser.com/Search/Produc...6Evirtualkey58810000virtualkey588-SV-LED-176E
Was looking at using either the IS1006-0820 or the IS1006-1025
I'm not concerned about legal issues. They will essentially be "fog lights" and there is nothing illegal about using them on the roads as long as they are not in folks's eyes.
I'm not concerned about thermal protection either as the driver will be mounted on the opposite side of this heatsink:
http://www.mouser.com/Search/Produc...6Evirtualkey58810000virtualkey588-SV-LED-176E
Was looking at using either the IS1006-0820 or the IS1006-1025
DIWdiver
Flashlight Enthusiast
Re: Adjustable 10A linear constant current driver
That heatsink should be suitable, as long as the airflow over it never drops below 10 mph. In still air, it would rise to around 275 C, which wouldn't be good at all.
Unfortunately, the heatsink isn't the only problem. If you run one LED on an IS1006-0820, the driver will dissipate about 80W. Short of soldering the FET directly to the heatsink (which would then require that you electrically isolate the heatsink), there's no way to get that much heat out of the FET and into the heatsink without unacceptable temperature rise. The practical limit is around 30W, which is about what you get running three LEDs in series.
If building fog lamps, I strongly suggest you read this first.
That heatsink should be suitable, as long as the airflow over it never drops below 10 mph. In still air, it would rise to around 275 C, which wouldn't be good at all.
Unfortunately, the heatsink isn't the only problem. If you run one LED on an IS1006-0820, the driver will dissipate about 80W. Short of soldering the FET directly to the heatsink (which would then require that you electrically isolate the heatsink), there's no way to get that much heat out of the FET and into the heatsink without unacceptable temperature rise. The practical limit is around 30W, which is about what you get running three LEDs in series.
If building fog lamps, I strongly suggest you read this first.
