Seek particular power supply solutions for chip test

Hello Chaunyu,

Suggest using a constant current source.  this will ensure a linear slope of your choosing based off an assume known load and a capacitance.

You will however need to ensure that the current sourcing circuit is disengaged when the power supply is operational and engaged and powered throughout the power down sequence.  please refer to the circuit shown below.  

The circuit in figure 4 ensures a linear slope because it will cause the buck to regulate the current when the loop is fed back in this manner.  for the purpose of this answer, please ignore Vz.  Again this loop needs to be disengaged when the power supply is in normal operation and as the voltage drops to low levels, this may cause the op amp to stop working and will cause non linearity to the discharge slope, hence the recommendation to keep it powered by external means to keep the op amp "alive".  

Another Scheme you can implement that maybe a little more straight forward is to implement a amplifier and a transistor circuit, see concept below.

Again this will need to be connected and disconnect in circuit as needed and bias supply needs to be permanent.

Hope this helps?

David.

Hello Chuanyu,

How was the modification implemented?  Was the circuit hand wired to implement modification?  If so, there could be issues related to poor routing and noise.  Will need to make sure that the feedback resistor R9 in the schematic above is position close to the input to the error amplifier.  If you are still having problems, please pot a picture of how the modification was implemented and also post a schematic of components and their values.

Thanks,

David. 

Sounds good Chuanyu,

If the circuit is hand wired, it is unlikely to work without noise interaction.  Need to ensure that the circuit is laid out to minimize noise introduced to the loop.  Please do try and please feel free to reopen thread should you still have issues.

Thanks,

David.

Hello Chuanyu,

The question originally poised was regarding constant current.  That is to say, you are regulating the current.  The voltage adjustment will depend on the load impedance, however we are not adjusting the voltage per se.  We have many devices that regulate current.  Suggest looking for LED driver devices on Ti.com.  see link below.

https://www.ti.com/power-management/led-drivers/overview.html

Hope this helps?

David.