# LCD Supply Current Queston

Discussion in 'General Electronics Chat' started by park1231, Aug 10, 2010.

1. ### park1231 Thread Starter New Member

Jul 24, 2010
3
0
Hi, I just received a DisplayTech 204a 4x20 LCD from a friend and found the data sheet here: http://www.pmb.co.nz/downloads/lcd_204a_series.pdf

My question is regarding the Supply Current for Logic (Idd) given on page 3. It states that the typical current is 1.44ma to a max of 4ma. Are these current measurements derived by dividing the input voltage at Vdd by the total resistance of the LCD circuit assuming that Vss goes to ground 0V?

If so will dividing the max supply Voltage of 5.5V by the max supply current of 4mA give me the total resistance (Thevinin resistance?) of the LCD circuit (1.375Kohms)?

So is it correct that if I were to place a resistor between a voltage source and Vdd of the LCD, the current between the voltage source and Vdd would not be an important consideration so long as the node voltage at Vdd falls within the recommended limits?

Sorry if these questions seem trivial, but I am new to this and trying not to fry this thing and appreciate any help.

2. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
201
Typical current can be taken as two things:

1) The average amount of current it will draw from a given voltage supply under operating conditions or, most likely,

2) An operatintg window of current that the device prefers to be operated within.

In this case I believe they're trying to to give you some guidelines for the minimum and maximum current the logic circuitry desires depending on how many segments you're lighting.