Comparator with adjustable hysteresis

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Hello,

I have to built a current source that controls the current in a coil. I  
want to built a ripple regulator that measures the current by a  
hall-sensor and switches the half bridge high side on if the current is  
too low and switches the half bridge low side on if the current is too  
high. Dead time to prevent cross-conduction is in the driver.

I need a high switching frequency for small currents (100kHz @ 20A) and  
a low switching frequency for high currents (20kHz @ 200A). I have to  
use a current control to have a permanent over current protection.

I want to realize this by adjusting the hysteresis of the comparator.
(see http://www.ti.com/lit/an/snva170b/snva170b.pdf,  Page 2,  Figure 3)

The only schematic I found was this:
https://www.google.com/patents/US5166550

PLEASE has someone a schematic of a comparator with adjustable  
hysteresis for me. Best would be a ground referenced voltage input for  
the hysteresis adjustment.

THANKS for your help!!!!

Best Regards
Harald

Re: Comparator with adjustable hysteresis
On Fri, 04 Nov 2016 09:18:26 -0700, Harald Noack wrote:

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Cost no object?  Less than a dime per unit?  What?

It seems that such a dramatic change in frequency with load is both  
unnecessary and would lead to more switching losses at low loads -- but  
I'm not you, so maybe there's a sensible reason.

Parts of the NE555 essentially work like a comparator with a wide  
hysteresis with one switching point adjustable.  Would your concept work  
with a comparator that has each switching point adjustable?  If so, you  
may be able to do something clever with a pair of comparators and an RS  
flip-flop, like the innards of a 555.

--  

Tim Wescott
Wescott Design Services
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Re: Comparator with adjustable hysteresis
On Fri, 4 Nov 2016 09:18:26 -0700 (PDT), Harald Noack

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There are some comparators with analog-programmable hysteresis, but a
more flexible approach is to use two comparators driving an RS
flipflop. You can set the upper and lower trip points anywhere.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Triangle.JPG


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Comparator with adjustable hysteresis
On Fri, 4 Nov 2016 09:18:26 -0700 (PDT), Harald Noack

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See my patent, 3,638,041 Sample and Hold Trigger Circuit, PDF near
bottom of my home page.  Hysteresis value is proportional to a current
source.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: Comparator with adjustable hysteresis
On Friday, November 4, 2016 at 12:18:33 PM UTC-4, Harald Noack wrote:
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Hmmmm- "Hall-Effect Sensor IC Bandwidth ?  Today, the usable bandwi
dth of most linear Hall ICs is ? 20 kHz. Signal voltage changes lit
tle up to this frequency. However, noticeable phase shift becomes distinct  
at somewhat lower frequencies. Some variation is apparent amongst different
 ICs and vendors, but the rolloff is quite steep beyond ? 20 kHz. A
lthough the cutoff frequency for the ?3 dB rolloff of all linear HE
Ds is inconsistent, 20 kHz to 25 kHz is a valid approximation."

http://www.allegromicro.com/en/Design-Center/Technical-Documents/Hall-Effec
t-Sensor-IC-Publications/Non-Intrusive-Hall-Effect-Current-Sensing-Techniqu
es-for-Power-Electronics.aspx

Re: Comparator with adjustable hysteresis
On Friday, 4 November 2016 16:18:33 UTC, Harald Noack  wrote:
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The classic approach to adding hysteresis is to divide the output with 2 Rs & feed that to +in. It's fairly obvious one can adjust the divider with 1 or more FETs. This is fairly trivial, you don't say what the issue is.

Re: Comparator with adjustable hysteresis
Thanks for all your posts!!!!

I used 2 comparators + 74hc74 + some current-mirrors an resistors

Best Regards  
Harald  

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