LM317 Adjustable Regulator Question

'595, which makes 1x 'AC04 per 2x '595. Then just distribute the low-level 5V square wave around the board to the inverters.

I like to learn new stuff. What's the objection to emitter followers?

They are non-stock, and only provide 25 mA per gate. You need six of = them to=20 get about 1 amp. So at $0.53 each that's $3, and a lot of board space. = Here=20 is a circuit using four transistors and four resistors, that provides a=20 solid square wave with 1.8A peak into the LEDs, simulated by a 2 ohm=20 resistor.

Here is the simulation with schematic and waveforms:

You can download the ASC file from:

This is much more efficient than a linear source/sink voltage regulator, =

which would draw 2.5 watts at 1 amp. Of course the LED resistors are = another=20 source of wasted power, but a PWM circuit is not really practical unless =

efficiency is critical.

Paul=20

What does "Stock:1,287 Can Ship Immediately" mean?

How the heck do you do that with transistor ratings of 600mA absolute maximum collector current?

can

'595, which makes 1x 'AC04 per 2x '595. Then just distribute the low-level 5V square wave around the board to the inverters.

The LED current drive was orig> > >> > >>>>

can

'595, which makes 1x 'AC04 per 2x '595. Then just distribute the low-level 5V square wave around the board to the inverters.

can

'595, which makes 1x 'AC04 per 2x '595. Then just distribute the low-level 5V square wave around the board to the inverters.

You can't rail them, and the peak current is now doubled from 560mA to 1.12A due to 50% duty (worst case).

They are non-stock, and only provide 25 mA per gate. You need six of them to get about 1 amp. So at $0.53 each that's $3, and a lot of board space. Here is a circuit using four transistors and four resistors, that provides a solid square wave with 1.8A peak into the LEDs, simulated by a 2 ohm resistor.

Here is the simulation with schematic and waveforms:

You can download the ASC file from:

This is much more efficient than a linear source/sink voltage regulator, which would draw 2.5 watts at 1 amp. Of course the LED resistors are another source of wasted power, but a PWM circuit is not really practical unless efficiency is critical.

Paul

Nice. Something else to try. Thanks Paul and everyone else for this spirited discussion.

Mike

It is correct and a contribution. No harm, no foul. BTW thanks.

?-)

OopS! My bad. I read the "on order" quantity.

Those were just models that were conveniently in the LTSpice list. I = could=20 have used the 2N3055. But the best parts would be Darlingtons like:

and

But it's still probably better to use a MOSFET gate driver like this =

1.5A=20 device, in a tiny SOT236 package, for $0.59/1:

Paul=20

On 6/21/2012 5:50 PM, snipped-for-privacy@gmail.com wrote: snip

due to 50% duty (worst case). You're saying that you can't design an emitter follower that can dissipate 0.6W average?

You don't need to email me your posts. I know how to find the newsgroup.

due to 50% duty (worst case).

Don't know if design is the word for it- the problem is the slop in output voltage magnitude is a substantial percentage of the total you want to deliver to the LEDs, and he's already working with fairly small current limiting resistors.

due to 50% duty (worst case).

voltage magnitude is a substantial percentage of the total you want to deliver to the LEDs, and he's already working with fairly small current limiting resistors.

Well, you've got 4V to work with. The original design had 2.5V. I don't know the Vf of the leds in use, but that looks like a substantial improvement in volts across the resistor. I estimate we've gone from "maybe works if you tweak it just right" to "throw it together and it works". If I were gonna build 10,000/month, I'd sure want to do some more thinking about it.

o 1.12A due to 50% duty (worst case).

up.

put voltage magnitude is a substantial percentage of the total you want to = deliver to the LEDs, and he's already working with fairly small current lim= iting resistors.

e

Actually the 30-40 ohm channel output resistance of the HC(T) works out to = be about right for a 2.5V drive and the most common red/green bicolor LEDs = with Vf in the 2.0-2.2V range for If~10mA, meaning no external resistors ar= e required. There will probably be more uncertainty in light output due to = the LEDs than the 595s making it kind of pointless to do any more than that= . Power dissipation-wise, the 5V square is no more efficient than the 2.5V = rail splitter, all it does is spread the waste energy to a mass of resistor= s that are otherwise unnecessary.

What is the Rc and Rcs? I have some 337's on order and will be trying this along with some of the other ideas suggested.

Mike

'595, which makes 1x 'AC04 per 2x '595. Then just distribute the low-level 5V square wave around the board to the inverters.

that load is now double, so you're looking at over 1.1A peak source/sink (70 LEDs). That's getting up there for a driver that can't be saturated.

'595, which makes 1x 'AC04 per 2x '595. Then just distribute the low-level 5V square wave around the board to the inverters.

'595, which makes 1x 'AC04 per 2x '595. Then just distribute the low-level 5V square wave around the board to the inverters.

due to 50% duty (worst case). I have no idea what it is that concerns you about the output of that timer not reaching the rail? If you need a rail signal in the high state, you simply put a pull up R from the Vcc to the output. This is of course, if you don't need a heavy drive.

Jamie

1.12A due to 50% duty (worst case).

voltage magnitude is a substantial percentage of the total you want to deliver to the LEDs, and he's already working with fairly small current limiting resistors.

about right for a 2.5V drive and the most common red/green bicolor LEDs with Vf in the 2.0-2.2V range for If~10mA, meaning no external resistors are required. There will probably be more uncertainty in light output due to the LEDs than the

595s making it kind of pointless to do any more than that. Power dissipation-wise, the 5V square is no more efficient than the 2.5V rail splitter, all it does is spread the waste energy to a mass of resistors that are otherwise unnecessary.

I prefer more robust designs. Putting a bunch of stuff with exponential V-I curves in series to a power supply makes me nervous. I'm partial to designs that use components in their intended/specified mode, can breeze thru the production process and are never heard from again.

Your idea of operating the logic from the +/-2.5 supplies and GND'ing the common junction of the LEDs is the least parts intensive and most reliable thus far.

Thanks! I'm happy to hear someone likes that idea. I'm just a hobbiest with some electronics schooling 35 years ago. I really appreciate that comment!

Mike

.

to 1.12A due to 50% duty (worst case).

roup.

utput voltage magnitude is a substantial percentage of the total you want t= o deliver to the LEDs, and he's already working with fairly small current l= imiting resistors.

n't

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to be about right for a 2.5V drive and the most common red/green bicolor L= EDs with Vf in the 2.0-2.2V range for If~10mA, meaning no external resistor= s are required. There will probably be more uncertainty in light output due= to the LEDs than the 595s making it kind of pointless to do any more than = that. Power dissipation-wise, the 5V square is no more efficient than the 2= .5V rail splitter, all it does is spread the waste energy to a mass of resi= stors that are otherwise unnecessary.

You'll be quoting the Bible next with all that 'intended/specified mode' no= nsense. Why don't you try reviewing the concept of load lines, then you mig= ht see driving the LEDs directly with logic outputs is nothing to get in a = panic over.

On Mon, 18 Jun 2012 22:06:21 -0400, "MFudalla" wrote:

--- The 595 can only sink or source a maximum of 35mA per pin or a total of 70 mA through Vcc or GND, so if you have 8 LEDs being driven per package, that means the current through them should be limited to 8.75 mA each.

In one of your posts you mentioned an LED current of 8mA, so I guess you figured that out already. :-)

For 70 LEDs, that would be a total of 613 mA from the supply, and with

2V across each of the LEDs, the series resistors would be about 343 ohms each. 360 ohms is a standard value and would allow 8.3mA through the LEDs, with a total drain on the 5V supply of 581mA.

In order to keep from having to split the supply, someone mentioned using an oscillator driving a half-bridge totem pole at a rate high enough to prevent flicker as your display changed.

Something like this:

Version 4 SHEET 1 1596 748 WIRE -128 -816 -256 -816 WIRE 160 -816 -128 -816 WIRE 464 -816 160 -816 WIRE 752 -816 464 -816 WIRE 880 -816 752 -816 WIRE 752 -784 752 -816 WIRE 880 -688 880 -816 WIRE 624 -672 560 -672 WIRE 736 -672 688 -672 WIRE 752 -672 752 -720 WIRE 752 -672 736 -672 WIRE 832 -672 752 -672 WIRE 1120 -576 1072 -576 WIRE 1216 -576 1184 -576 WIRE 1312 -576 1280 -576 WIRE 1424 -576 1376 -576 WIRE 560 -560 560 -672 WIRE 608 -560 560 -560 WIRE 736 -560 736 -672 WIRE 736 -560 688 -560 WIRE -128 -528 -128 -816 WIRE 160 -480 160 -816 WIRE 208 -480 160 -480 WIRE 528 -480 432 -480 WIRE 880 -464 880 -592 WIRE 912 -464 880 -464 WIRE 1072 -464 1072 -576 WIRE 1072 -464 992 -464 WIRE 208 -416 32 -416 WIRE 496 -416 432 -416 WIRE 560 -368 560 -560 WIRE 608 -368 560 -368 WIRE 736 -368 688 -368 WIRE -128 -352 -128 -448 WIRE 32 -352 32 -416 WIRE 32 -352 -128 -352 WIRE 64 -352 32 -352 WIRE 160 -352 128 -352 WIRE 208 -352 160 -352 WIRE 560 -352 560 -368 WIRE 560 -352 432 -352 WIRE 1072 -352 1072 -464 WIRE 1120 -352 1072 -352 WIRE 1216 -352 1184 -352 WIRE 1312 -352 1280 -352 WIRE 1424 -352 1424 -576 WIRE 1424 -352 1376 -352 WIRE -128 -320 -128 -352 WIRE 880 -320 880 -464 WIRE 464 -288 464 -816 WIRE 464 -288 432 -288 WIRE 560 -240 560 -352 WIRE 624 -240 560 -240 WIRE 736 -240 736 -368 WIRE 736 -240 688 -240 WIRE 752 -240 736 -240 WIRE 832 -240 752 -240 WIRE 1424 -224 1424 -352 WIRE -256 -208 -256 -816 WIRE -128 -208 -128 -240 WIRE 64 -208 -128 -208 WIRE 160 -208 160 -352 WIRE 160 -208 128 -208 WIRE 160 -192 160 -208 WIRE 496 -192 496 -416 WIRE 496 -192 160 -192 WIRE 752 -192 752 -240 WIRE 160 -176 160 -192 WIRE -256 -96 -256 -128 WIRE 160 -96 160 -112 WIRE 160 -96 -256 -96 WIRE 528 -96 528 -480 WIRE 528 -96 160 -96 WIRE 752 -96 752 -128 WIRE 752 -96 528 -96 WIRE 880 -96 880 -224 WIRE 880 -96 752 -96 WIRE 1424 -96 1424 -144 WIRE 1424 -96 880 -96 WIRE -256 -32 -256 -96 FLAG -256 -32 0 SYMBOL Misc\\NE555 320 -384 M0 SYMATTR InstName U2 SYMBOL cap 176 -176 M0 WINDOW 0 -33 32 Left 2 WINDOW 3 -39 58 Left 2 SYMATTR InstName C2 SYMATTR Value 1µ SYMBOL diode 64 -336 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL diode 128 -224 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D4 SYMATTR Value 1N4148 SYMBOL res -112 -544 M0 SYMATTR InstName R8 SYMATTR Value 4.7K SYMBOL nmos 832 -320 R0 SYMATTR InstName M2 SYMATTR Value FDS6930A SYMBOL voltage -256 -224 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL res -112 -336 M0 SYMATTR InstName R1 SYMATTR Value 4.7K SYMBOL pmos 832 -592 M180 SYMATTR InstName M1 SYMATTR Value FDS6685 SYMBOL voltage 1424 -240 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 24 96 Invisible 2 SYMATTR Value PULSE(0 5 0 1u 1u 100ms 200ms) SYMATTR InstName V2 SYMBOL res 1008 -480 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 180 SYMBOL diode 688 -256 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D5 SYMATTR Value 1N4148 SYMBOL res 704 -384 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL cap 736 -192 R0 SYMATTR InstName C1 SYMATTR Value 100n SYMBOL diode 624 -656 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D7 SYMATTR Value 1N4148 SYMBOL res 704 -576 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL cap 736 -784 R0 SYMATTR InstName C3 SYMATTR Value 100n SYMBOL diode 1120 -560 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 1216 -560 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL diode 1312 -560 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D6 SYMATTR Value 1N4148 SYMBOL diode 1184 -368 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D8 SYMATTR Value 1N4148 SYMBOL diode 1280 -368 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D9 SYMATTR Value 1N4148 SYMBOL diode 1376 -368 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D10 SYMATTR Value 1N4148 TEXT -32 -56 Right 2 !.tran .5 startup uic TEXT 440 -496 Left 2 ;1 TEXT 440 -432 Left 2 ;2 TEXT 440 -368 Left 2 ;3 TEXT 440 -312 Left 2 ;4 TEXT 184 -304 Left 2 ;5 TEXT 184 -368 Left 2 ;6 TEXT 184 -432 Left 2 ;7 TEXT 184 -496 Left 2 ;8

Notice that since the duty cycle is 50%, the currents are allowed to be twice normal, with 16mA peak available into the LEDs for the same brightness as 8mA, CW.

A few more components and the brightness of the red and green could be equalized, if that's important.

BTW, what LEDs are you using/do you have a link to their data sheets?

-- JF

1.12A due to 50% duty (worst case).

voltage magnitude is a substantial percentage of the total you want to deliver to the LEDs, and he's already working with fairly small current limiting resistors.

be about right for a 2.5V drive and the most common red/green bicolor LEDs with Vf in the 2.0-2.2V range for If~10mA, meaning no external resistors are required. There will probably be more uncertainty in light output due to the LEDs than the 595s making it kind of pointless to do any more than that. Power dissipation-wise, the 5V square is no more efficient than the 2.5V rail splitter, all it does is spread the waste energy to a mass of resistors that are otherwise unnecessary.

nonsense.

Why don't you try reviewing the concept of load lines, then you might see driving the LEDs

directly with logic outputs is nothing to get in a panic over.

No panic here. If you've done the math and it works for you, use it. You'll have no worries from me until you invite me to one of your design reviews. That's not likely to ever happen.

Second notice: Please stop emailing me stuff.