Segment LED driving using shift Register SN74HC595DR

Arulmurugan Paramasivam99

Prodigy 10 points

Other Parts Discussed in Thread: TPIC6C595

Using SN74HC595DR Shift Register we are driving the 7 segment display and switching at around 70Hz.

Supply voltage = 5V

Switching Frequency = 70Hz

Series Resistor value = 39ohms

Peak Voltage drop across series resister is 1.2V

Current per channel - 30.7mA.

Current at 8 channel - 245mA

But as per absolute maximum rating per channel 35mA and total current from all channel is 70mA continuous only.

Please suggest or provide details about what would be Switching current capability per channel and total switching current .

Best Regards

Arulmurugan P

over 6 years ago

0 Dylan Hubbard over 6 years ago

TI__Mastermind 46045 points

Hi Arulmurugan,

It is recommended to have no more than 6 mA of output current at 5 V. Running the device close the the abs max ratings could damage the part or affect reliability. I don't recommend driving the 7-segment directly with this device instead I would add in a buffer to provide more drive strength.

0 Clemens Ladisch over 6 years ago

Guru 317370 points

For such high currents, you need a power logic device, e.g., TPIC6C595.

0 ShreyasRao over 6 years ago

TI__Guru 62280 points

Arulmurugan,

You could also refer to these TI designs on LED driving using the shift register:

Logic

Logic forum

Segment LED driving using shift Register SN74HC595DR