John Fields wrote:
On Thu, 12 Apr 2007 10:19:14 -0500, "Anthony Fremont"
wrote:

MassiveProng wrote:
On Thu, 12 Apr 2007 04:55:30 -0500, "Anthony Fremont"
Gave us:

Chances are that the
display was only being driven by 12V. Just imagine how long they
would last in a vehicle seeing 14V all the time.

If the drive circuit was designed properly, they should be able to
be the same brightness for a voltage range of say 7 to 16 volts.
That would be what a good designer would build anyway. A regulated
front end on the circuit would be required to achieve any
repeatability with the final product.

Since we're already here and everything, can you show me a schematic
of how to do that?

---
Simple. constant current source.
---

No fair if others help.

---
Aw, heck... :-(


Version 4
SHEET 1 880 680
WIRE 96 -48 -64 -48
WIRE 224 -48 96 -48
WIRE 96 32 96 -48
WIRE 224 32 224 -48
WIRE 224 176 224 96
WIRE 224 176 192 176
WIRE 96 224 96 112
WIRE 128 224 96 224
WIRE 224 272 192 272
WIRE -64 352 -64 -48
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WIRE -64 576 -64 432
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FLAG -64 640 0
SYMBOL npn 128 176 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL npn 192 352 M0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL LED 208 32 R0
SYMATTR InstName D1
SYMATTR Value NSPW500BS
SYMBOL res 80 16 R0
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL res 208 432 R0
SYMATTR InstName R2
SYMATTR Value 36
SYMBOL voltage -64 336 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(7 16 0 1)
TEXT -58 608 Left 0 !.tran 1.1

I wondered if you'd do the long-tail pair or use an LM317, now I know.
That's how the manufacturer should do it, but do you think they "waste" all
that money on two transistors just to do it right? I mean their profit
margin is only something like 95% as it is. ;-)