[General] MAX6955 7-Segment Driver with 10V 4" LED Display

[Jonathan2015]

Hi,
I am using a number of I2C devices on a board. One is a MAX6955 I2C 7-segment display driver. This operates from 2.7V to 5.5V, but the 4" common cathode 7-segment LEDS require 7.2V to operate. The MAX6955 outputs sink current when acting as digit drivers, source current when acting as segment drivers, or are high impedance when not being used. I am driving 4 digits so a couple of the outputs will be used to source and sink current.
I am struggling to design a circuit to interface between the MAX6955 and the 7-segment displays, to switch the outputs to a higher voltage.
Any suggestions please?

 

[KlausST]

Hi,

wow, is that IC available? and not too expensive?

to your question:
I don´t think there is an easy solution to drive your 7.2V displays with this IC.

Sorry.

Klaus

 

[ads-ee]

Take a look at this , you might be able to use a few of these to drive the display depending on how much current it needs.

 

[Renato Toi]

I have used optocouplers successfully for 7.2 VDC led display. https://www.vishay.com/docs/83526/83526.pdf

 

[KlausST]

Hi,

I have used optocouplers successfully for 7.2 VDC led display. https://www.vishay.com/docs/83526/83526.pdf

The optocouplers need a lot of drive current. Three times the display current.
How did you connect it to the high side outputs of the MAX6955?

Klaus

 

[Renato Toi]

I have connected arduino output ports as current sinks.

 

[niji99]

Hi,

My first post on here. I hope I can offer you a solution to drive 4" seven segment leds but it is slightly different to your requirements. Insofar as my solution uses common anode LED's. There are solutions for driving high voltage leds with the max chips, but they involve quite a lot of added circuitry current sinks/sources etc. So I looked for another solution and came up with the WS2803 LED strip driver chip. You can apply up to 40V dc on the anode. Only draw back on this chip is the segments are not multiplexed so full current is drawn all the time. Writing code is fairly easy as in my case I only used 8 outputs from the 18 available on the WS2803 for my pcb design. chip control is via 2 inputs SDin and CKin and full words need to be sent to the chip so even though using 8 outputs all 18 outputs need to be controlled, i.e. 8 on 12 off. I have tried to describe this a bit better on this video. https://youtu.be/5BYZ51pFNXY Apologies in advance if it doesn't match your requirements, but I feel that it may be a solution.

Nick