Hi folks
Long time no post.
Wise Steve K drew my attention to his post.
Before you read the next bit, do realise I may be completely wrong...
...when I say that a voltage output dc-dc converter with linear feedback (eg LM46002) is not a great option for connecting what is effectively a constant current source to a constant voltage load.
The feedback loop does not know where to go.
- or are you going to force the feedback using MPPT or feed-forward?
It is a shame that no one makes something similar - integrated oscillator, level-shifter, driver stage and output mosfets - but with an external input controlling the PWM ratio - it would be so useful for this kind of application.
Unfortunately, we have to home-brew all this, with all the attendant switching losses
- and the need to hand-craft dead-band timing (to prevent both mosfets being 'on' momentarily causing large, efficiency-eating, current spikes).
That said, the advanced PWM available in several PICs, and probably some AVRs, will at least handle PWM and dead-band, still leaving the rest to be sorted.
BTW1
using 2x n-mosfets in a buck means that either you can never achieve 100% duty-cycle for Vout=Vin, or you need a separate power rail to feed the upper gate.
Using a p-mosfet in the upper position allows 100% operation.
BTW2, regarding bridge rectifiers:
Rather than use a four-mosfet active bridge rectifier, plus a Schottky, why not use two mosfets and two Schottkys?
You get the same voltage drop, reverse-blocking, and save two mosfets.
Plus, with separate mosfets you get the chance to protect the gates with resitors and Zeners.
And, I have to add a plea - please don't make bike lamps which dazzle other road users - almost anything powerful using rotationally-symmetric optics will be guilty of this.
Another Steve
Long time no post.
Wise Steve K drew my attention to his post.
Before you read the next bit, do realise I may be completely wrong...
...when I say that a voltage output dc-dc converter with linear feedback (eg LM46002) is not a great option for connecting what is effectively a constant current source to a constant voltage load.
The feedback loop does not know where to go.
- or are you going to force the feedback using MPPT or feed-forward?
It is a shame that no one makes something similar - integrated oscillator, level-shifter, driver stage and output mosfets - but with an external input controlling the PWM ratio - it would be so useful for this kind of application.
Unfortunately, we have to home-brew all this, with all the attendant switching losses
- and the need to hand-craft dead-band timing (to prevent both mosfets being 'on' momentarily causing large, efficiency-eating, current spikes).
That said, the advanced PWM available in several PICs, and probably some AVRs, will at least handle PWM and dead-band, still leaving the rest to be sorted.
BTW1
using 2x n-mosfets in a buck means that either you can never achieve 100% duty-cycle for Vout=Vin, or you need a separate power rail to feed the upper gate.
Using a p-mosfet in the upper position allows 100% operation.
BTW2, regarding bridge rectifiers:
Rather than use a four-mosfet active bridge rectifier, plus a Schottky, why not use two mosfets and two Schottkys?
You get the same voltage drop, reverse-blocking, and save two mosfets.
Plus, with separate mosfets you get the chance to protect the gates with resitors and Zeners.
And, I have to add a plea - please don't make bike lamps which dazzle other road users - almost anything powerful using rotationally-symmetric optics will be guilty of this.
Another Steve
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