[SOLVED] Turn off Low Impedance Equipment before turning off DC supply

[ParkerMike]

Why is it a Rule to turn off low impedance Test equipment before turning off a DC power supply?

What are some low impedance test equipment?

I heard a pulse generator is a low impedance test equipment

If you turn off the DC power supply before turning off a low impedance test equipment it can damage the ow impedance test equipment, but why?

 

[ashugtiwari]

When you switch ON and OFF the power supply, there is a sudden discontinuous change in power levels in power supply, just like surge. This discontinuity can inrush some high current into equipments. So, in equipments with low impedance, the current will be very high with this high discontinuous surge current and this can damage the device. For eg. when you turn ON and OFF the DC power to music system, the woofer and sub woofer gives a click/tap sound, and this sound depends on the inrush surge current due to sudden change in power levels. But, i guess woofer's can handle this. In old movie theaters, you can still hear the tap sound in their woofers, when they switch on the complete system.

Hope that helps.

 

[chuckey]

This is all very well but a properly designed equipment will be able to be switched on and off at the mains. Else it would self destruct if you had a break in the mains supply.
Frank

 

[KlausST]

Hi,

if you want to test a logic device and at its input there is a pulse generator...
Then switch off the power supply of the dut, but the signal of the pulse generator still remains on the dut´s input.
Now current is flowing from dut input via protectionn diodes to VCC of dut, if there is any other load at the VCC then the protection diodes may be overdriven.

It is just be be on the safe side...

Hope that helps
Klaus