Need help with Low voltage protection circuit
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Re: Need help with Low voltage protection circuit
Reproduction royalties to ... guess.
As far as I know this *should* work but no guarantees. Circuit on the left is the cutoff circuit, right is the original circuit. If you plan to hack the existing board, be careful there are subtile differences.Attached FilesLast edited by eccerr0r; 08-16-2020, 09:47 PM.Comment
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Re: Need help with Low voltage protection circuit
I could try scrounging one off a board if they had readable identification marks."...off the record, unnamed government sources
alluded to unsubstantiated innuendos about
alleged indiscretions and insinuated that they
are rumored not to be without basis for further
speculation..."Comment
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Re: Need help with Low voltage protection circuit
12V is fine, just needs to be less than 20V (Vgsmax) but above 5V (Vgsth). Circuit is poorly tuned and behavior/power consumption can be improved by changing component values. Should be able to get it less than 10mA draw, but at 10mA it's still pretty horrible. This also depends on voltage input too.
Note that the diode will limit current draw value, probably should omit that 1N4007 and short it out.
Again, no guarantees. It still has the problem of being setpoint dependent behavior though it should be somewhat linear, and because of this I did not do threshold value calculations.
Also the 1M resistor is probably superfluous, the zener itself should be sufficient to turn the mosfet off.Last edited by eccerr0r; 08-17-2020, 11:09 AM.Comment
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Re: Need help with Low voltage protection circuit
I used 3 5.1v zeners in series. I do not have the IRF9540n in the schematic and am using my IRF5305.
I have tested the circuit and since my power supply cannot go much higher than 19 volts (I have a better one on the way). I have the pot connected to In+, in-, and pin 3 of the lm358 set so that the transistor turns off at 17.26v and on at 16.3v.
The mosfet gate voltage is 6v when the transistor turns off, and 8.5v when it turns on.
The mosfet seems to be on all the time.
The second 10k pot seems to do nothing."...off the record, unnamed government sources
alluded to unsubstantiated innuendos about
alleged indiscretions and insinuated that they
are rumored not to be without basis for further
speculation..."Comment
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Re: Need help with Low voltage protection circuit
I'd expect the second pot to do very little, it should change the voltage spread slightly.
Do not use three zener diodes in series. The circuit depends the single zener to discharge the gate - if wired correctly, should drop below 1V (with respect to source, of course.)
Also it should be mentioned that the voltage at pin 3 will change depending on the voltage at pin 1. What's unfortunate about this and the original circuit is that ideally the amplifier is running at fixed voltage instead of the varying voltage to ensure the behavior of the circuit is reliable.
Ensure the voltage at pin 1 will switch between IN- plus around ~0.2V to IN+ minus ~1.5V. If it doesn't, something is wrong.Last edited by eccerr0r; 08-17-2020, 12:52 PM.Comment
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Re: Need help with Low voltage protection circuit
I'd expect the second pot to do very little, it should change the voltage spread slightly.
Do not use three zener diodes in series. The circuit depends the single zener to discharge the gate - if wired correctly, should drop below 1V (with respect to source, of course.)
Also it should be mentioned that the voltage at pin 3 will change depending on the voltage at pin 1. What's unfortunate about this and the original circuit is that ideally the amplifier is running at fixed voltage instead of the varying voltage to ensure the behavior of the circuit is reliable.
Ensure the voltage at pin 1 will switch between IN- plus around ~0.2V to IN+ minus ~1.5V. If it doesn't, something is wrong.
I then started over and rebuilt the design in your pdf from scratch again on my breadboard.
The differences between mine and yours are:
transistor is a 9014n I also tried a BC550 (accounted for pin differences) I do not have a pn2222a
mosfet is IRF5305
12v zener
removed 1n4007
Hysteresis is still a little over 1v which is good.
Nothing I do short of dropping the supply voltage below 10v shuts off the mosfet.
The behavior of the circuit is like this:
Changing the supply voltage causes 9014n to turn on at 17.44v and off again at about 18.55.
At the same time the voltage coming out of the transistor is 7.67vdc, AND at the same time voltage rises on the gate of the mosfet from about 8.4 to about 8.59 then drops back to 6.97 AND at the same time voltage on pin 1 of the lm358 goes from .076v to about 17.12v instantly.
It looks something like this when graphed:
edit graph removed because it is wrong.
just in case I did something dumb and don't see it here is pics:
Last edited by flinx; 08-17-2020, 02:42 PM."...off the record, unnamed government sources
alluded to unsubstantiated innuendos about
alleged indiscretions and insinuated that they
are rumored not to be without basis for further
speculation..."Comment
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Re: Need help with Low voltage protection circuit
here is the corrected graph I hacked together in excel that illustrates what is going on.
"...off the record, unnamed government sources
alluded to unsubstantiated innuendos about
alleged indiscretions and insinuated that they
are rumored not to be without basis for further
speculation..."Comment
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Re: Need help with Low voltage protection circuit
oh fiddlesticks this is what happens when I don't play with discrete P-channel devices and assume it works like PNP. You're right, there's a problem there, really need to have simulated it and got my current directions wrong. I'm still not going to simulate since there's no warranty expressed or implied :-P
Now I was hesitant on doing the lower left no-BJT version in the first place, though it may well just work. Do not use a "logic level" MOSFET here, IRF9540 and your IRF5305 should work fine. If you you have to use a logic level or the no-BJT version doesn't work, try the upper left version with three BJTs.Attached FilesLast edited by eccerr0r; 08-17-2020, 03:52 PM.Comment
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Re: Need help with Low voltage protection circuit
IT VERKS! IT'S VERKING!
hysteresis is about 1.09v second pot has barely any measurable effect. maybe .04 volts?
But it VERKS!
now if my power supply would ever get here from china I could set the voltages proper.
To easyeda!
Can the lm393 be substituted for the lm358? pinouts are the same."...off the record, unnamed government sources
alluded to unsubstantiated innuendos about
alleged indiscretions and insinuated that they
are rumored not to be without basis for further
speculation..."Comment
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Re: Need help with Low voltage protection circuit
So you are using the lower left circuit utilizing both opamp?
What is the DCV at output pin 1 and pin 7 when it is not trip and when it trips?Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: Need help with Low voltage protection circuit
For LM358, when not tripped pin 1 should be around the same voltage as pin 8, minus 1.5 volts or so. This was my main concern for direct driving in the first place.
Pin 7 should be no more than 0.2V.
When tripped, swap the voltages around.
Dang if this really doesn't exist anywhere I should productize this. But this is a ridiculously simple circuit and those chinese mass producers will beat me to the punch. Grr.Last edited by eccerr0r; 08-17-2020, 05:44 PM.Comment
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"...off the record, unnamed government sources
alluded to unsubstantiated innuendos about
alleged indiscretions and insinuated that they
are rumored not to be without basis for further
speculation..."Comment
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Re: Need help with Low voltage protection circuit
I look look at your first circuit:
When battery Voltage is good, the pot is set so the + INPUT (3) is >5.1Vref on the -INPUT (2) so Output (1) swings high (max out = VCC - 1.5V per spec) which turns on the 2N2222 and P-CH MOSFET since now the Gate is toward ground providing > 3V Vg-s.
When battery goes low to the point that - INPUT (3) is < 5.1V, the Output (1) will switch low (0.2V) which will cause the 2N2222 and MOSFET to be off.
Am I missing something?
I think the error is in OP post #46:
I have the pot connected to In+, in-, and pin 3 of the lm358 set so that the transistor turns off at 17.26v and on at 16.3v.Attached FilesNever stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: Need help with Low voltage protection circuit
circuit board
with 1oz traces it can handle about 8 amps, with 2oz it can handle 13, and with a 12 gauge bare copper wire soldered to the bottom traces for b- to out- and b+ to source it should be able to handle at least 20 amps.
The mosfet would be laid down, soldered to the board and the output wire taken directly from the tab.
board is 2.6"x1.4" I'm sure it could be made much smaller with SMD but that's not my bag.
also I would most likely not be using this with anything below 14 volts."...off the record, unnamed government sources
alluded to unsubstantiated innuendos about
alleged indiscretions and insinuated that they
are rumored not to be without basis for further
speculation..."Comment
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Re: Need help with Low voltage protection circuit
You should put down Thermal Vias for the MOSFET.
Is the copper plane as heatsink for the MOSFET large enough for it to handle 20A or are you going to use heatsink to keep MOSFET junction at safe temperature?
Also consider VIA Stitching for high current.
https://www.microtype.io/high-power-...n-tips-tricks/Last edited by budm; 08-17-2020, 07:13 PM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
-
Re: Need help with Low voltage protection circuit
I look look at your first circuit:
When battery Voltage is good, the pot is set so the + INPUT (3) is >5.1Vref on the -INPUT (2) so Output (1) swings high (max out = VCC - 1.5V per spec) which turns on the 2N2222 and P-CH MOSFET since now the Gate is toward ground providing > 3V Vg-s.
When battery goes low to the point that - INPUT (3) is < 5.1V, the Output (1) will switch low (0.2V) which will cause the 2N2222 and MOSFET to be off.
Am I missing something?
I think the error is in OP post #46:
I have the pot connected to In+, in-, and pin 3 of the lm358 set so that the transistor turns off at 17.26v and on at 16.3v.Comment
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