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Old 30th December 2005, 10:25 PM   #11
Danko is offline Danko  Hungary
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Eva, you wrote:
Quote:
an op-amp capable of swinging its output to ground is required for that purpose.
So, do I need a "rail-to-rail" opamp?


I will think about this current-limiting thing... I would like to limit the max. output current, but now you mentioned, that this does not protect the switches from overcurrent.
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Old 31st December 2005, 11:57 AM   #12
Danko is offline Danko  Hungary
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Hello!


I attached the modified schematic.
I circled the D2 diode. What type of diode should it be? 1N4148 is OK here? Or it must be a low forward voltaged diode? Maybe germanium-diode?

I put a blue X on the schematic. If I put there a current sense resistor, is that OK?
But ... I have seen many dc/dc buck regulator schematics. Thoose circuits were current limited, voltage stabilized. And i have never seen on them, that there's a current measuring on the input-rails of the circuit.

The opamps are right on the schematic?

Eva, thank you, your opinions, ideas, help!
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Old 31st December 2005, 02:10 PM   #13
Eva is offline Eva  Spain
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The diode is placed backwards, and you are still sensing output current instead of inductor current... You have improved, though
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Old 31st December 2005, 02:32 PM   #14
Danko is offline Danko  Hungary
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Hello!


Why is the that D2 diode backwards? In the TL494 datasheet, there the diode is connected the same way, as I draw. (see the attached image)

I think I will "implement" the inductor-current-sensing in the next version of this "experiment".
But I still don't understand, why I haven't seen any buck-regulator circuits with input-current-sensing. Is it too expensive? Or it degrades the efficiency too much?
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Old 31st December 2005, 03:31 PM   #15
Eva is offline Eva  Spain
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In a TL494 increasing COMP voltage causes duty cycle to decrease. In a SG3525A increasing COMP voltage causes duty cycle to increase. That's why the diode is backwards for a SG3525A.
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