Need help increasing hysterisis for comparator circuit - Electronic Circuits Projects Diagrams Free

1abeng · 18th June 2009, 04:16 PM

This circuit determines which voltage supply to switch to the motor - solar panel (SUN+) or power supply (24V+). My comparator circuit is toggling on/off when the +V IN is near the -V IN (6.5V). It cycles very fast.

Can anyone give advice on preventing the toggle? Circuit is attached.

Thanks in advance

Chippie · 18th June 2009, 04:18 PM

Looks to me like there's no feedback around the controlling comparator... U4.1, but I could be wrong..

See the attached sketch

1abeng · 18th June 2009, 04:21 PM

I can't claim the design. It is a prototype product for me. I tried a few feedback options but I don't know enough to select the right components or put them in the right place.

ericgibbs · 18th June 2009, 04:21 PM

Quote:

Originally Posted by 1abeng

This circuit determines which voltage supply to switch to the motor - solar panel (SUN+) or power supply (24V+). My comparator circuit is toggling on/off when the +V IN is near the -V IN (6.5V). It cycles very fast.

Can anyone give advice on preventing the toggle? Circuit is attached.

Thanks in advance

hi,
Usually adding a resistor between pins 1 and 3 of the comparator will add hysteresis.
Start with a high value, say 470K,, the lower the value the greater the 'dead band'.

EDIT: if you do add hysteresis you may have to readjust the SUN on/off points!!

ericgibbs · 18th June 2009, 05:54 PM

hi 1ab,
This are the results from a LTspice simulation.

The results dont agree with what you say on the circuit diagram.???

Check thru this LTS circuit, the caps have been omitted for clarity.

What colour is the LED 'D2' on my circuit.???

1abeng · 18th June 2009, 06:29 PM

Thank you for your review! The D2 color is green, D1 is Yellow. The Vsun doesn't react the same as the simulation. As soon as the load is removed, the voltage shoots up past the upper threshold but it can't generate the current to keep it above the bottom threshold when it switches back. I connected a resistor (180ohm/5W) across the +Vsun and -Vsun when not in SUN mode (same trigger as relay K1) to keep the voltage down but it required a delay-on-release relay (50ms) to work. There must be a better way.

Thanks again.

BrownOut · 18th June 2009, 06:31 PM

Quote:

Originally Posted by ericgibbs

hi 1ab,
This are the results from a LTspice simulation.

The results dont agree with what you say on the circuit diagram.???

Check thru this LTS circuit, the caps have been omitted for clarity.

What colour is the LED 'D2' on my circuit.???

I thought it was U1 that needed the feedback?!?!

EDIT: Ok, I see where the hysteresis is coming from now. Never saw it done that way before. Duh!

MrAl · 18th June 2009, 06:38 PM

Hi,

The placement of C23 is part of the problem because it prevents the
snap action of the hysteresis from working properly. The design should
be changed to eliminate this cap or to modify the hysteresis feedback.

One way might be to place the hysteresis resistor (of the right value)
between pins 1 and 3 and let the LED section go without any hysteresis.
This way the cap C23 can be left there for a little filtering.
You also need to add some resistance between pin 3 and the two
caps connected to that pin so the hysteresis works properly.

ericgibbs · 18th June 2009, 06:43 PM

Quote:

Originally Posted by 1abeng

Thank you for your review! The D2 color is green, D1 is Yellow. The Vsun doesn't react the same as the simulation. As soon as the load is removed, the voltage shoots up past the upper threshold but it can't generate the current to keep it above the bottom threshold when it switches back. I connected a resistor (180ohm/5W) across the +Vsun and -Vsun when not in SUN mode (same trigger as relay K1) to keep the voltage down but it required a delay-on-release relay (50ms) to work. There must be a better way.

Thanks again.

hi,
The point I noted was the switching points, the sim makes these 4V and 10V.!

The voltages marked on the circuit marked at point Vr dont agree with the sim.

EDIT:
I'll re-run sims with C4, also introduce the offload jump OK, let you know the result.

BTW: making D2 a green LED, changes the limits to 4V and 11V

ericgibbs · 18th June 2009, 06:47 PM

Quote:

Originally Posted by BrownOut

I thought it was U1 that needed the feedback?!?!

hi,
The circuit uses the upper LM393 to provide the hysteresis for the first LM393.

The range is +4V and +10V according to the LTS sim,

BrownOut · 18th June 2009, 06:49 PM

Quote:

Originally Posted by ericgibbs

hi,
The circuit uses the upper LM393 to provide the hysteresis for the first LM393.

The range is +4V and +10V according to the LTS sim,

Right! Took me a moment to realize that. Never saw it done that way before.

ericgibbs · 18th June 2009, 06:54 PM

Quote:

Originally Posted by BrownOut

Right! Took me a moment to realize that. Never saw it done that way before.

Its a nice method to get such a wide hysteresis limit.

1abeng · 18th June 2009, 07:24 PM

I'm not sure what the difference is. The actual circuit switches at 4.5V and 13.1V.

Quote:

Originally Posted by MrAl

Hi,

The placement of C23 is part of the problem because it prevents the
snap action of the hysteresis from working properly. The design should
be changed to eliminate this cap or to modify the hysteresis feedback.

One way might be to place the hysteresis resistor (of the right value)
between pins 1 and 3 and let the LED section go without any hysteresis.
This way the cap C23 can be left there for a little filtering.
You also need to add some resistance between pin 3 and the two
caps connected to that pin so the hysteresis works properly.

MrAI, Are you talking about moving R29 to U4.1 pins 1 and 3 then adding R31 between pin 3 and C21 / C22? What value is needed for R31?

FYI - the circuit reacts very differently on the solar panel than on a power supply simulating the panel by restricting the current. The cycling is very fast when on the panel partially covered.

ericgibbs · 18th June 2009, 07:32 PM

hi 1ab,
With the high jump in SUN voltage when going off load, the circuit is definitely unstable when running in simulation.!

I'll see if I can suggest any changes,, it will be tomorrow OK.

1abeng · 18th June 2009, 07:41 PM

A 220KOhm resistor accross U4.1 pins 1 and 3 didn't make much difference. It may have slowed the cycling a little. I have limited resistor values to test.

If this works, what are the pros and cons of doing this:

Quote:

I connected a resistor (180ohm/5W) across the +Vsun and -Vsun when not in SUN mode (same trigger as relay K1) to keep the voltage down but it required a delay-on-release relay (50ms) to work.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar
Title	Starter	Forum	Replies	Latest
Increasing output current for charge pump circuit	eafindme	Electronic Projects Design/Ideas/Reviews	1	14th May 2009 12:37 PM
Comparator circuit + OP Amp 741 help	Hussain	Electronic Projects Design/Ideas/Reviews	10	22nd January 2009 12:50 PM
Comparator circuit	prprog	General Electronics Chat	22	5th June 2008 01:59 PM
Comparator Circuit	bigG	General Electronics Chat	4	22nd March 2007 10:52 PM
Comparator circuit	George L.	General Electronics Chat	3	21st June 2005 06:51 AM

18th June 2009, 04:16 PM	#1
1abeng	Need help increasing hysterisis for comparator circuit This circuit determines which voltage supply to switch to the motor - solar panel (SUN+) or power supply (24V+). My comparator circuit is toggling on/off when the +V IN is near the -V IN (6.5V). It cycles very fast. Can anyone give advice on preventing the toggle? Circuit is attached. Thanks in advance Attached Thumbnails

18th June 2009, 04:18 PM	#2
Chippie	Looks to me like there's no feedback around the controlling comparator... U4.1, but I could be wrong.. See the attached sketch Attached Thumbnails __________________ Eccentric millionaire financed by 'er indoors Last edited by Chippie; 18th June 2009 at 04:28 PM.

18th June 2009, 04:21 PM	#3
1abeng	I can't claim the design. It is a prototype product for me. I tried a few feedback options but I don't know enough to select the right components or put them in the right place.

18th June 2009, 05:54 PM	#5
ericgibbs	hi 1ab, This are the results from a LTspice simulation. The results dont agree with what you say on the circuit diagram.??? Check thru this LTS circuit, the caps have been omitted for clarity. What colour is the LED 'D2' on my circuit.??? Attached Thumbnails __________________ Eric " Good enough is Perfect " I will NOT answer PM's requesting technical help, please use the Forum PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 18th June 2009 at 05:56 PM.

18th June 2009, 06:29 PM	#6
1abeng	Thank you for your review! The D2 color is green, D1 is Yellow. The Vsun doesn't react the same as the simulation. As soon as the load is removed, the voltage shoots up past the upper threshold but it can't generate the current to keep it above the bottom threshold when it switches back. I connected a resistor (180ohm/5W) across the +Vsun and -Vsun when not in SUN mode (same trigger as relay K1) to keep the voltage down but it required a delay-on-release relay (50ms) to work. There must be a better way. Thanks again.

18th June 2009, 06:38 PM	#8
MrAl	Hi, The placement of C23 is part of the problem because it prevents the snap action of the hysteresis from working properly. The design should be changed to eliminate this cap or to modify the hysteresis feedback. One way might be to place the hysteresis resistor (of the right value) between pins 1 and 3 and let the LED section go without any hysteresis. This way the cap C23 can be left there for a little filtering. You also need to add some resistance between pin 3 and the two caps connected to that pin so the hysteresis works properly. Last edited by MrAl; 18th June 2009 at 06:40 PM.

18th June 2009, 07:32 PM	#14
ericgibbs	hi 1ab, With the high jump in SUN voltage when going off load, the circuit is definitely unstable when running in simulation.! I'll see if I can suggest any changes,, it will be tomorrow OK. Attached Thumbnails __________________ Eric " Good enough is Perfect " I will NOT answer PM's requesting technical help, please use the Forum PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 18th June 2009 at 07:35 PM.