EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Spikee on August 31, 2013, 12:55:16 am
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I'm currently designing a dc-dc converter tester (digitally controlled dummy load).
It does measure: Input voltage/current , output voltage/current but it would also be cool to measure the switching frequency of the regulator.
I already found a way to measure frequency using my Psoc 5LP processor, but it relies on ttl / cmos voltage levels to detect the frequency.
So i probably need a high pass filter and some amplification to get the voltage right and possibly something like a schmitt trigger
Or is there another way that would work better ?
Thanks
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if you just want the frequency and not the pulse width you can make a very simple amplifier that feeds a binary counter,
you ac couple your input through a capacitor and current limiting resistor,
you feed this into a npn transistor with its base biased through a high value resistor so its collector voltage just above the trigger point of the counters shmitt trigger, for a given lift up resistor,
and for good measure you add a diode with its anode to ground and cathode to the transistor base so it can handle large swings,
this leaves you with a very sensitve counter intended for swinging almost rail to rail and doesnt pick up much noise on high amplitude signals,
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You might look at the schematic in this post (https://www.eevblog.com/forum/projects/automatic-gain-control-or-%28agc%29-circuit-help/msg274408/#msg274408) for some ideas:
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If you are making an in circuit tester with pogo pins, then you can just measure the "input side" of the inductor, or the catch diode, with a small amplifier. Else it could be a bit tricky, if the output filter is built properly. You need to make an bandpass filtered (AC coupled), automatic gain amplifier there.
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I just finished with the digital part of the project and I will soon open a topic on this forum about it.
Also I don't know if it is useful to measure it for evaluation purposes.
The features I have currently implemented:
-Measure input voltage
-Measure input current
-Measure output voltage
-Measure output current (dummy load)
-4 temperature measurements inputs (heatsink , switching converter , pcb etc ...)
This should give you efficiency , load characteristics ,transient response ...
Noise measurement may be a more useful thing to add.
I have successfully built a dummy load before that could handle 400W and was tested up to 63A now i am just making it more precise and nicer.
The 20bit adc in the Psoc 5LP will give me plenty resolution now I am just looking at the analog stage for the load and my opamp selection. All that will be discussed when I open a thread about it.
b.t.w. Your nandblog is awesome
And all of you thanks for the replies !