Large 7-segment OLED

Why OLED instead of conventional LED?

Power consumption.

visibility without backlighting. I was hoping to find single or several digit displays to make a large clock module with only a few W consumption.

I don't know if it's just a matter of time before these appear or if there's a technology constraint in making large OLED segments.

Viktor

conventional LEDs, so at the same brightness, a conventional LED should have lower power.

It's more likely simple economics - the market for jumbo LEDs is relatively tiny, (and primitive) and anyone developing OLED displays will chase the larger revenue streams first.

How large a display are you after, on what power budget ?

-jg

Are OLEDs actually any more efficient than standard LEDs for the same light output? I suspect probably not. OLEDs typically compete with LCDs, which throw away at least 50% of th backlight light in the polariser, and then about 60% mode in the RGB filters. Not hard to compete with that with a light-emitting product.

A few W will run a bunch of (carefully chosen) normal LEDs pretty darn bright. And it will last longer - OLEDs still have some lifetime issues ISTR.

Thanks for the answers everybody. I must admit, I've never actually seen a real live OLED so all my information is hazy at best. I imagined it to be something like an LCD with its own light source. So, I thought that in bright light it would have a reflective component like LCDs (I've worked with some big LCDs for petrol station pump displays and they are very good at high ambient light.)

The largest 7-segment LED display I found (LITEON) had a 76mm digit height and was stated at 30mcd/20mA. With four digits, and about 20 segments, that would be about 5W. I can just about manage that, but it wouldn't be at its brightest and it would probably be poor in daylight.

So, is it just wishful thinking or do OLEDs have a reflecive function like LCDs?

Viktor

5W for 20 segments @ 20mA doesn't sound right. At 1 Volt forward voltage, the power is 20mW/segment, or 400 mW total. I don't know the LITEON specs, but even if Vf is somewhat higher, you don't get close to 5 W.

Of course, if you add in the dissipation in the series resistor, total power will be higher, but you can reduce that by using a lower drive voltage made from a switching power supply (use a SimpleSwitcher for instance), in combination with a smaller resistor.

If you multiplex the displays, you can use a higher peak current, so the resistor can be even smaller, resulting in lower losses.

Six LEDs in series for each segment. The chart gives 20mA If @ 12V Vf.

Ah, I see.. that makes sense.

However, at 30mcd/20mA, these aren't the most efficient. There are single LEDs that are a few thousand mcd, at lower power. Perhaps you can make your own display by taking some state of the art LEDs, and mount them behind some diffusing plastic yourself ?

4" seven-seg displays are pretty common - I think I've also seen 6 & 8"

If you need best readability for minimum power, you may want to look at using slim lines of discrete LEDs ( e.g. PLCC-2/4 types) as the segments , so the light is more concentrated & contrast is maximised.

No, they don't.

Best regards, Spehro Pefhany

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For a nice looking clock display see

If you need large segments , this way maybe cheaper and brighter than buying

8" seven segment displays(also powered from 12V)

Alex