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I would like to build a DCDC Converter with an adjustable Output Voltage and adjastable Current Limitation.
Key Specs:
My idea is to Manipulate the Feedback path of a DCDC Controller to adjust the Output Voltage throuth inserting current through a DAC.
Since the application has no need for high speed current limitation, i thought about regulating current through adjusting the Voltage.
But the problem is the resulting Current Resulution for small load resistance. Since the DCDC Converter will be used for charging low ESR batteries lets assume a Output Resistance of 20mOhm.
If i am having a Voltage Resolution of 10mV the resulting Current Resulution will be 500mA. Witch is not acceptable.
The simplest solution would be an additional Series Resistor to increase the output ESR, but the downside is a lot of powerloss and nessasary cooling.
I think there should be a discrete Solution to the problem but i can not think of one.
Mazbe someone has an idea how to manipulate the feedback with 2 DACs, resulting in current and voltage limitation.
Thanks for your help :)
Hi Rico,
What is the chemistry of the batteries you plan to use in your application? Most lithium ion batteries use a CCCV charging profile where output current is regulated until a max charging voltage is reached (around 4.2V per series-connected cell) and then output voltage is regulated. A typical discrete implementation is to use two feedback loops: one loop sets the max charging current, the other sets the max charging voltage. Take a look at PMP4963 as an example (U3A is the voltage feedback loop, U3B is the current feedback loop):
Many of the bq devices integrate both the current error amplifier and the voltage error amplifier to save space such as bq24133:
Does this answer your question?
Best Regards,
Ben Lough
