# What protection measures to consider when switching many loads at the same time with shift registrers?

I'm developping a programmable load board with many of these load steps to test LDO or DC/DC converter Output.

As you can see, what changes is the resistor R6 to provide other current load values. The inputs of the transistors are the outputs of two shift registers (I'm using the 74HC595 Shift register from NXP. ). The LED is an extra to see the status directly on the board.

I'm concerned about the latching of the output from the shift registers to the transistors and how the load value transition looks. It will change many loads at the same time with different current values changing from on to off and vice versa. The total load will be measured at the output of the LDO as the total of the currents flowing in the resistors. I dont't have inductive elements in my circuit , but are there some tips with which I can optimize the current value transitions? Is this enough as it stands ?

Thank you !

• Any infos about the shift register and the transistor? As well as what you do mean by as smooth and unproblematic as possible. Also you're the one who knows the required R6 values because you know what you'll be testing, or am I missing something here? – HatimB Feb 15 '17 at 11:05
• thanks, I added some informatio9n and tried to clarify my question. – nesrine ghajati Feb 15 '17 at 15:55

Don't forget to check if your driving voltages are greater than the MOSFET's Vgs which will make it operate in its linear region $(Vds = Rds*Id)$.