I try to understand this datasheet: Datasheet

How it's can be possible to have in parallel (1 led) and (2 led in serie) without resistor for the led alone?


Here the only "datasheet" that I found: https://datasheet.lcsc.com/szlcsc/1-2inch1bit-Red-digital-LED_C53679.pdf



Here what is inside:

Led segment circuit

  • \$\begingroup\$ It's certainly not what you'd expect. I can only assume that (a) the datasheet's low-quality and wrong or (b) it's right and the LEDs are matched such that the single LED has the same drop as the two series LEDs, in each case. Maybe this is possible if all three LEDs are on the same silicon in each case. But I have no obvious answer to your question. \$\endgroup\$ – TonyM Jan 19 '18 at 18:01
  • \$\begingroup\$ Well... strictly speaking, none of those are LEDs, just regular diodes. \$\endgroup\$ – Finbarr Jan 19 '18 at 18:15
  • \$\begingroup\$ Please add a link to the data sheet \$\endgroup\$ – Trevor_G Jan 19 '18 at 18:51

Its possible, but why they did this is hard to say. (if in fact this is the actual diagram, it is a one color LED so this could be correct). If the diagram is drawn correctly, at a lower voltage only the red LED will conduct and the two in series will be off. At a higher voltage all three will be on but the LED that is not in series will be getting more current. Since nothing else is known about the LED's (no voltage, color, or IV curve) nothing can be said of the actual operation.

This may make more sense if the LED's were two different colors.

If you use this you'll need to provide current limiting with a circuit or resistor.

You could find the IV curve but increasing the current in steps and measuring the voltage,and that would tell you more about this terribly undocumented product.

  • \$\begingroup\$ +1 for "if in fact this is the actual diagram" indeed, I would suspect the drawing is representational to understand the connection only. Without the actual link to the data sheet, or more information about the drive requirements it is impossible to say for sure. \$\endgroup\$ – Trevor_G Jan 19 '18 at 18:55
  • \$\begingroup\$ I think that is the datasheet, I searched for more, but couldn't find any additional info. But not having any more information would be consistent with most Chinese sourced products, \$\endgroup\$ – Voltage Spike Jan 19 '18 at 19:06
  • \$\begingroup\$ Ya I found a link on some provider, but they needed me to register.... screw that ;) \$\endgroup\$ – Trevor_G Jan 19 '18 at 19:08
  • \$\begingroup\$ Possibly the LEDs in serie are red, green or orange (2*1.8V = 3.6V) while the single LED is blue (3V). At 3V the blue lit up. At 3.6V all 3 lit up, blue and red or only the red ones thanks to voltage drop. It's possible that when the red ones lit up, the blue one shut down. \$\endgroup\$ – Fredled Jan 20 '18 at 22:29

Looks to me like they made the PCB (and the datasheet) so they could include either one LED die or two series LED dice per segment.

Since the color is stated as red (红) the forward voltage should be around 1.8-2V for one LED and around double that for two in series.

Since the display is relatively large (1.2 inch 英寸) it would be more even and brighter with two LEDs, but the forward voltage may be too high for some applications, particularly if they used the same PCB for green, blue or white- in which case even 5V is not enough.

So you can easily figure out which of the two it is by measuring the forward voltage at a reasonable current (5 or 10mA). It's a bit hard for me to see from your photo but it does look to me like two are fitted in series and the third is not populated.


Normally you would expect an datasheet to indicate wavelength, Vf, If, Luminous Intensity (mcd) etc etc.

Also you would expect the Decimal Point, DP to be small compared to the segment, but not expect 2 diodes shunted by 1.

My guess is the supplier has 2 sources , one with 1 single diode per segment and another with 2 and since Vf is not given, you have to guess. It is normal for digits larger than 1" to have 2, 3, or 4 LEDs in series for the segments and 1 or 2 for the DP and 1 or 2 in series for < 1" in RED 7seg + DP displays.

This drawing is obviously WRONG.

My Guess, all series chips.

Here all they tell you is the pinout and mechanical dimensions of each segment and list it as

"1.2inch 1bit Red digital LED "


Distributor with poor drawing skills has misrepresented the part.

To me it looks like someone with primitive engineering skills made a drawing with 3 LEDs per segment and made it your guess for multiple source.

How desperate are you to buy poorly documented parts?

enter image description here

  • 1
    \$\begingroup\$ This weekend you'll walk through shops and see cheap and not-cheap electrical toys and gadgets made from poorly documented parts like these by the lorry load. This stuff ain't from some 'other world' that we don't live in but the desperate do :-) \$\endgroup\$ – TonyM Jan 19 '18 at 21:36
  • \$\begingroup\$ Having done custom LED's with custom datasheets and private label for 10yrs, I recognize the signs of a poor datasheet. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 19 '18 at 22:50
  • \$\begingroup\$ Fair enough but that wasn't my point, not to worry \$\endgroup\$ – TonyM Jan 19 '18 at 22:59
  • \$\begingroup\$ Yes I was just re-asserting that the datasheet has many things lacking and is at fault, just like most broker sales on Ebay. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 19 '18 at 23:02
  • \$\begingroup\$ @TonyStewart.EEsince'75 Oh, you'll find the same thing exactly when you walk in and talk to them at the market stalls in China. \$\endgroup\$ – Spehro Pefhany Jan 20 '18 at 20:11

Judging by the photo of the internals you supplied the datasheet is right! (Your schematic diagram is not correct.)

enter image description here

Figure 1. The LED arrangement highlighted for one segment.

  • LED 3 and 1 are in series between the anode pin (orange) and the cathode (blue).
  • LED 2 is directly between the anode and cathode.


simulate this circuit – Schematic created using CircuitLab

Figure 2. Schematic of one segment.

Maybe 1 and 3 are a fallback for when 2 burns out! It certainly is strange.


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