# How much power needs to light up the LEDs?

Discussion in 'Troubleshooting and Repair' started by pandadnap, Jan 10, 2018.

3
0
Jan 10, 2018
Hi all,
I am new to here and layman to electronics. Hope i am not asking a stupid question.
I have a device like this. What i want to do is to light up those LEDs. The question is I don't know how much power(Voltage and current) it needs. Is it possible to guess by just look at the circuit?
thank you everyone!
Panda

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010

You don't need much power, but you need to apply it correctly.

3. ### 73's de Edd

3,121
1,315
Aug 21, 2015
Sir pandadnap . . . . .

Look at the CN1 connector vewy-vewy closely and observe its pin 1 connection, that receives the + terminal of a 9V battery.
The Pin 2 connection goes to the batteries - terminal.

That will then be giving you the prescribed operational / brightness parameters that Sony had it made to work at.

Expect about a 150 ma, hefty drain upon your battery . . . . . unless you opt for a 9VDC wall wart for its power supply.

Thasssssit . . . .

73's de Edd

Last edited by a moderator: Jan 11, 2018
4. ### Avishek

3
0
Jan 10, 2018
It’s usually between 2 and 3 volts and it depends on the color and type of LED

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
One thing you can tell by looking is that there must be 7 strings of 2 LEDs.

That means the voltage you need to apply is at least twice the voltage each individual LED requires.

The series resistor in each string acts to limit the current at a particular applied voltage. Because these are not high power LEDs, you can typically assume the current will be no more than about 20mA per LED. Because there are 7 strings, the total current will probably not exceed 140mA at the voltage this panel was designed to operate at (Edd's post no doubt assumed this to be the case).

If you trace the circuit you should be able to verify the configuration, and by applying a variable voltage (say from a bench power supply) you should be able to determine the voltage at which 140mA is drawn (again, Edd suggests this will be around 9V). You could also measure the forward voltage of one of the LEDs (observing the colour can often be close enough because there are typical voltages for most colors) and do some calculations involving the series resistor value to calculate an expected operating voltage.

LEDs are not always operated at the maximum current (although they should not be operated continuously above it) so the current at the rated voltage might be lower than 20mA per LED (or 140 mA in total).

3
0
Jan 10, 2018
Thank you (*steve*), 73's de Edd and Avishek for the feedback.

Avishek - that are red LEDs

(*steve*), 73's de Edd - If i understand correctly, is that mean if i use a variable DC adapter, by adjusting the output voltage, I should get them light up at certain voltage? (for example, 9V suggested by 73's de Edd)

Last edited by a moderator: Jan 10, 2018
7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
They may start to light up at about 3 volts and get brighter and brighter as the voltage increases.