# Question: LED DISPLAY 7-SEG. RED SA40-19SURKWA

#### Vitrivius

Nov 30, 2022
2
Hello,

I've recently bought led 7 segment displays for a counter project including shift registers and an Arduino.
This project will include 5 seven segment displays each with a forward voltage of 7.4V and a max current of 10 mA,
so my question is do i need to multiply the input voltage or the current by 5 to get the correct values?

I have include the technical data sheet for more detail.

Any help would be greatly appreciated

#### bertus

Moderator
Nov 8, 2019
2,792
Hello,

Those are large displays with multiple leds in one segment.
That is why the forward voltage is 7.4 Volts.
The stated current is for each segment.
If all segments are on there will be 7 X 10 mA drawn from the supply = 70 mA for each display.
Also if the decimal point is used, extra current will be drawn.
The decimal point has a lower forward voltage of about 3.7 Volts.

See the datasheet for all details.

Keep in mind that you will need a driver to use the displays, as the arduino can not drive the 7.4 Volts displays directly.
A TBD62083 could be used a driver.

Bertus

#### Attachments

• TBD6208X.pdf
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• SA40-19SRWA.pdf
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#### Vitrivius

Nov 30, 2022
2
Hello,

Those are large displays with multiple leds in one segment.
That is why the forward voltage is 7.4 Volts.
The stated current is for each segment.
If all segments are on there will be 7 X 10 mA drawn from the supply = 70 mA for each display.
Also if the decimal point is used, extra current will be drawn.
The decimal point has a lower forward voltage of about 3.7 Volts.

View attachment 57148

See the datasheet for all details.

Keep in mind that you will need a driver to use the displays, as the arduino can not drive the 7.4 Volts displays directly.
A TBD62083 could be used a driver.

Bertus
Hi Bertus,

So if i hook up 5 of these i need a power source of 7.4 volts and 350 mA, is that correct?
For the display divers i'm using a TPIC6B596N.

Thank you for your precious time.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,884
Typically the parameter "forward current" refers to one segment. So a single 7-segment digit with decimal point can draw up to 80 mA when fully lit.
5 of these displays will draw up to 5 × 80 mA = 400 mA incl. decimal point or 350 mA without decimal point.

The usual configuration to drive such a display (5 7-segment units) is by multiplexing. This saves a considerable number of wires and output ports from the controller. Read e.g. here about multiplexing LEDs.
Of course, as each unit is "on" only 1/5 of the time, it would be considerably darker. Therefor ethe peak current is increased to match the brightness to a non-multiplexed display. In your application the peak current would be increased to 50 mA per segment (and decimal point). But since inly one unit is ever on at a time, the total current is still 400 mA (or 350 mA).
The higher peak current (50 mA vs. the specified 10 mA from the datasheet) is not an issue. The average current is still only 10 mA due the 1/4 on/off ratio from the multiplexing. LEDs, specially the ones usd in such displays, can easily withstand the higher peak current as the average power and thus the heating from this power stays the same.

 You will also need current limiting, usually resistors are used. The current limiting resistor (or an equivalent current source) will require a minimum voltage drop to work correctly. Therefore your power supply should be more like 8 V. With exactly 7.4 V there is no room left for the current limiting circuit.

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