LM317 Adjustable Regulator Question

My bad. I extrapolated from "Outputs are tri-state."

If off is not required, your problem just got simpler. Put a resistor in series with each led and tie the other end to a square wave 0-5V. All your voltage tolerance and current matching/limit problems just went away. If your red/green leds aren't the same brightness, you can tweak the duty factor to make it so.

It's an original Texas Instruments part, the TLE2426 Rail Splitter.

Cheers

Phil Hobbs

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Is that the hydraulic one ?:-) ...Jim Thompson

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I love to cook with wine.     Sometimes I even put it in the food.

turn up

5

and

volt

shift

close

how

comments

Something wrong there - National's datasheet says 3V:

Ed

A tiny synchronous switcher would do the job. You could set the voltage to optimize the current through the different LEDs, to get visually uniform brightness for the two colors. It would be a lot more efficient than a linear regulator.

A synchronous switcher is like a pair of gears: it can pump power in either direction.

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Tristate the inverter => output is high-Z = no current in LED.

Please don't top-post.

dn't

of an

up

2.5

side

or

volt

ate

I was thinking about this on the drive home. (slow day?) If you don't like the resistor, you can flip the circuit over. The 317 sources 2.5 volts and let the IC go low to turn the led on. (Assuming the IC can sink the LED current.)

George H.

317 output goes here o------o | |o .-. | | | | 1k | | | '-' | | | | | 1N914 V | - | | | | | 1N914 V o - | | |/ o--o-| 2N2222 | |>

| | o o .-. | | | | 10k | | | '-' | o o | |o o--o---o | o === GND

That is ~ 2.5 volt clamp.. It'll kick in as a sink when needed!

Yes, It works and I know I am weird.!

Jamie

This I should be able to try tomorrow.

Hope it never gets above 50C or so.

Tim

-- Deep Friar: a very philosophical monk. Website:

turn

5

out and

volt

shift

close

not how

comments

You're right. I was looking at the conditions at the top of the spec table. My bad. Art

need. Also, this=20

will ultimately=20

Yabbut, opamps that will sink or source 1 A or so are not all that cheap. then again neither are 595s.

?-)

"Artemus" wrote in message news:jroqkr$ic9$ snipped-for-privacy@dont-email.me...

Here's a simple circuit that may need to be tweaked, but can source and = sink=20 up to one amp or so:

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D Version 4 SHEET 1 1020 680 WIRE 128 32 -64 32 WIRE 256 32 128 32 WIRE 256 64 256 32 WIRE 128 112 0 112 WIRE 192 112 128 112 WIRE -64 128 -64 32 WIRE 0 144 0 112 WIRE 256 176 256 160 WIRE 320 176 256 176 WIRE 480 176 400 176 WIRE 256 192 256 176 WIRE 480 192 480 176 WIRE 0 240 0 224 WIRE 128 240 0 240 WIRE 192 240 128 240 WIRE -64 320 -64 208 WIRE 128 320 -64 320 WIRE 256 320 256 288 WIRE 256 320 128 320 WIRE 480 320 480 272 WIRE 480 320 256 320 FLAG -64 320 0 SYMBOL npn 192 64 R0 WINDOW 0 44 29 Left 2 WINDOW 3 37 67 Left 2 SYMATTR InstName Q1 SYMATTR Value 2N3019 SYMBOL pnp 192 288 M180 WINDOW 0 44 66 Left 2 WINDOW 3 32 37 Left 2 SYMATTR InstName Q2 SYMATTR Value D45H11 SYMBOL res 112 16 R0 SYMATTR InstName R1 SYMATTR Value 25 SYMBOL res 112 224 R0 SYMATTR InstName R2 SYMATTR Value 25 SYMBOL voltage -64 112 R0 WINDOW 3 -5 56 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL voltage 480 176 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value PULSE(0 5 100u 40n 40n 100m 200m 20) SYMBOL res 304 192 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R3 SYMATTR Value 2 SYMBOL res -16 128 R0 SYMATTR InstName R4 SYMATTR Value 50 SYMBOL diode 112 112 R0 WINDOW 3 33 39 Left 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 112 176 R0 WINDOW 3 35 26 Left 2 SYMATTR InstName D2 SYMATTR Value 1N4148 TEXT -98 344 Left 2 !.tran 500m startup

inverters basically behave like an op-amp with the non-inverting input connected somewhere between the defined logic levels (the inverting input is the inverter input)

in --+----[bi-color-led]--. | | | |\ | `-|-\ | 2-3V-+- | \_______________| | | / `---|+/ |/

The negative feedback will put the inverting input close enough to the output that very little current flows through the LED.

--
?? 100% natural

=3D red,

Clever.

-- Cheers, James Arthur

Well, you've got to do something. You might not like the extra parts, but tell that to the LEDs--they don't care!

The inverter is virtual--it could be as simple as a single BSS138 or

2n7002.

-- Cheers, James Arthur

"P E Schoen" wrote in message news:jrrf96$inb$ snipped-for-privacy@dont-email.me... "Artemus" wrote in message news:jroqkr$ic9$ snipped-for-privacy@dont-email.me...

Here's a simple circuit that may need to be tweaked, but can source and sink up to one amp or so:

========================================================= Version 4 SHEET 1 1020 680 WIRE 128 32 -64 32 WIRE 256 32 128 32 WIRE 256 64 256 32 WIRE 128 112 0 112 WIRE 192 112 128 112 WIRE -64 128 -64 32 WIRE 0 144 0 112 WIRE 256 176 256 160 WIRE 320 176 256 176 WIRE 480 176 400 176 WIRE 256 192 256 176 WIRE 480 192 480 176 WIRE 0 240 0 224 WIRE 128 240 0 240 WIRE 192 240 128 240 WIRE -64 320 -64 208 WIRE 128 320 -64 320 WIRE 256 320 256 288 WIRE 256 320 128 320 WIRE 480 320 480 272 WIRE 480 320 256 320 FLAG -64 320 0 SYMBOL npn 192 64 R0 WINDOW 0 44 29 Left 2 WINDOW 3 37 67 Left 2 SYMATTR InstName Q1 SYMATTR Value 2N3019 SYMBOL pnp 192 288 M180 WINDOW 0 44 66 Left 2 WINDOW 3 32 37 Left 2 SYMATTR InstName Q2 SYMATTR Value D45H11 SYMBOL res 112 16 R0 SYMATTR InstName R1 SYMATTR Value 25 SYMBOL res 112 224 R0 SYMATTR InstName R2 SYMATTR Value 25 SYMBOL voltage -64 112 R0 WINDOW 3 -5 56 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL voltage 480 176 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value PULSE(0 5 100u 40n 40n 100m 200m 20) SYMBOL res 304 192 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R3 SYMATTR Value 2 SYMBOL res -16 128 R0 SYMATTR InstName R4 SYMATTR Value 50 SYMBOL diode 112 112 R0 WINDOW 3 33 39 Left 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 112 176 R0 WINDOW 3 35 26 Left 2 SYMATTR InstName D2 SYMATTR Value 1N4148 TEXT -98 344 Left 2 !.tran 500m startup

How do I decode this? :-)

I like this too!

Tried this but didn't really like the result. I had to add an extra

1N914/1N4148 to keep it from clamping too early. With only 2, both regulators heated up in a hurry but it did clamp the heck out of my 2.5 volt regulator. With 3, still heating but a little slower. Also lost some of the clamping. This seems like a brute force type solution wasting power unnecessarily. I think I'll try the square wave idea next...