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qiushidaren Community Member Offline I am a lovely MOSFET! Posts: 86 Chengdu	DC/DC Used In BC3 Jun 14^th, 2008, 12:47am Hi folks, Long time no see, I have been ill for several months, this is the first time I return DGC, I miss you guys so much! I got a DC/DC circuit used in BC3, but I don't know what's its function and what's it used for, can you give me some suggestions? Best regards, Terry
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: DC/DC Used In BC3 Reply #1 - Jun 16^th, 2008, 1:23pm More information! Is that an op-amp or a comparator? Whats the input signal? Whereis the negative input to that op-amp connected? And, anything welse that you know.
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qiushidaren

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Re: DC/DC Used In BC3
Reply #2 - Jun 17^th, 2008, 11:49pm

loose-electron wrote on Jun 16^th, 2008, 1:23pm:

More information!
Is that an op-amp or a comparator?
Whats the input signal?
Whereis the negative input to that op-amp connected?

And, anything welse that you know.

The input signal is from the BC3 core, and the negative input to the op-amp is connected to a bias voltage generated by the bandgap in the DC/DC block, the figure shown below is the comparator used, VB is also a bias from the bandgap in the DC/DC.

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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: DC/DC Used In BC3 Reply #3 - Jun 23^rd, 2008, 12:52pm Detective hat on: What you have is a pass thru system (a source follower and not much else) up to a certain amplitude. Above a certain amplitude the comparator kicks in and limits the output. Not sure what it is getting used for, but at first glance thats what it does. Jerry
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qiushidaren

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Re: DC/DC Used In BC3
Reply #4 - Jun 23^rd, 2008, 8:03pm

loose-electron wrote on Jun 23^rd, 2008, 12:52pm:

Detective hat on:

What you have is a pass thru system (a source follower and not much else) up to a certain amplitude.

Above a certain amplitude the comparator kicks in and limits the output.

Not sure what it is getting used for, but at first glance thats what it does.

Jerry

Hi loose-electron,

You mean amplitude, not frequency? But there is a C1, in steady state, the right plane of C1 will be 0 voltage, can you give me some more details about how it works towards amplitude.

Best regards,
Terry

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loose-electron

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Re: DC/DC Used In BC3
Reply #5 - Jun 24^th, 2008, 11:29am

Up to a certain amplitude, yes. The system is AC coupled, so the frequency dependence is a matter of input signal and spectral content vs where the roll off point is of the ac coupling.

Spectral depedence is going to be tied to the relative locations of those two. My premise is that AC coupling exists only to remove the DC content. Best I can do depending on the limited data available.

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Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

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