Comparator with adjustable hysteresis

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

formatting link
Page 2, Figure 3)

The only schematic I found was this:

formatting link

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

Reply to
Harald Noack
Loading thread data ...

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 
 Click to see the full signature
Reply to
Tim Wescott

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.

formatting link

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
 Click to see the full signature
Reply to
John Larkin

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      | 
 Click to see the full signature
Reply to
Jim Thompson

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."

formatting link

Reply to
bloggs.fredbloggs.fred

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.

Reply to
tabbypurr

Thanks for all your posts!!!!

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

Best Regards Harald

Reply to
Harald Noack

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.