I came across a IT6533, its a DC auto ranging power supply in a lab.
It is a 200V 120A 6kW unit.
The dude using it told me that when he power off the unit, there is still a 3.4V on the output for like 15minutes before it gradually decrease to 0V.
This is way too long and i was somehow asked to solve this issue.

I knew i can use resistor to quicky discharge the 3.4V but how do i select the correct rating resistor to use?
I assume a discharge time of 10-15sec would be enough.
I know next to nothing on bleeder resistor so I google around but there are diff formulas and the more I read, the more ............. confuse i get.
I know some basic electrical stuffs but this is new to me.

Also this bleeder resistor have to be capable of supporting the unit in full load right?
Or it doesn't matter??

Appreciate any help i can get.

 

I wonder if you could connect a high voltage MOSFET which you could turn on with a separate circuit maybe powered by a 12V DC supply which drives the gate when the IT6533 voltage drops below 5V? In other words, an active approach rather than a fixed resistor.

 

The bleeder resistor has to waste power as heat when the PSU is operating at maximum voltage. Use Ohm’s Law to calculate the resistance based on current drawn.

For example,
1A @ 200V requires 200Ω 200W. Use greater than 300W.
0.1A @ 200V = 2000Ω 20W

 

Putting a bleeder resistor on the output of that supply will mess up your current readings.

When using a bench supply it is a good idea to always connect and disconnect the load with a separate series switch...for various reasons.

Personally, I would not be concerned 3.4 volts is not a dangerous voltage.

 

First question is "why is 3.4 volts when switched off a problem?? Certainly it is not a safety issue, 3.4 is not hazardous. The simple scheme that wastes very little power is to use a normally closed relay with a mains voltage coil to disconnect a 100 ohm bleeded resistor across the output when the supply is powered and active.