Under voltage detection

hp1729

Joined Nov 23, 2015
2,304
I have NCP300 with sft1341 mosfet. I want to monitor my battery at 3V. Does attached circuit work. I have a confusion how P channel MOSFET works with NCP300. Could anybody explain me working of this circuit.

Thanks
It looks like the SFT1341 might turn off before the NCP300 does if gate voltage drops too low.
Something like an IRLM110. Gate Threshold voltage is 1 to 2 Volts. The voltage needed to turn it on. The SFT1431 requires up to 4 Volts and may not turn on at all below 3.5 Volts.
NCP300 is surface mount? IRLM110 is too.
 
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Thread Starter

mishra87

Joined Jan 17, 2016
1,034
Thank you all for your support.

Finally i have decided to procure the component.

1. NCP301LSN30T1G - On Semi

And I still have a doubt about MOFET selection Whether it could be power or logic MOSFET.
Could you please recommend me appropriate part number which is suitable for my application so that i can move further.

Thank you !!!
 

hp1729

Joined Nov 23, 2015
2,304
Thank you all for your support.

Finally i have decided to procure the component.

1. NCP301LSN30T1G - On Semi

And I still have a doubt about MOFET selection Whether it could be power or logic MOSFET.
Could you please recommend me appropriate part number which is suitable for my application so that i can move further.

Thank you !!!
It has to turn on at under 3 Volts. That says Logic level gate. How much current do you need?
 

Thread Starter

mishra87

Joined Jan 17, 2016
1,034
It has to turn on at under 3 Volts. That says Logic level gate. How much current do you need?
In steady state condition of instrument the peak load current is 200mA but it has to withstand battery transient.

I am not more clear with the fundamental of selection of could you let me know that how to select a mosfet let's say about this applications.

Please recommend me MOSFET part number for NCP301LSN30T1G .
 

hp1729

Joined Nov 23, 2015
2,304
In steady state condition of instrument the peak load current is 200mA but it has to withstand battery transient.

I am not more clear with the fundamental of selection of could you let me know that how to select a mosfet let's say about this applications.

Please recommend me MOSFET part number for NCP301LSN30T1G .
200 mA is not a problem. IRLM110A can withstand 1.5 A.

Concerns ...
Gate threshold. It has to turn on below 3 Volts. The IRLM110A turns on at 2 Volts.
Maximum voltage (3 V is no problem)
Maximum current (200 mA means something bigger than a 2N7000 TO-92 package)
Case (surface mount, the NCP301 is also, right)
Resistance, source to drain. At 1.5 Amps the IRLM110A has 0.44 ohms. Probably much lower at only 200 mA. Something less than 0.05 ohms. So power to the device will drop only 10 mV through the transistor.
Speed? No problem at DC.
At 200 mA no heat sink is required.

Or find one that meets these specs.

(Maybe a BS170. TO-92 case but handles 500 mA. Oops, no. Resistance is 5 ohms. It would drop almost a volt across the transistor. So now you know what to avoid.)
 

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Thread Starter

mishra87

Joined Jan 17, 2016
1,034
200 mA is not a problem. IRLM110A can withstand 1.5 A.

Concerns ...
Gate threshold. It has to turn on below 3 Volts. The IRLM110A turns on at 2 Volts.
Maximum voltage (3 V is no problem)
Maximum current (200 mA means something bigger than a 2N7000 TO-92 package)
Case (surface mount, the NCP301 is also, right)
Resistance, source to drain. At 1.5 Amps the IRLM110A has 0.44 ohms. Probably much lower at only 200 mA. Something less than 0.05 ohms. So power to the device will drop only 10 mV through the transistor.
Speed? No problem at DC.
At 200 mA no heat sink is required.

Or find one that meets these specs.

(Maybe a BS170. TO-92 case but handles 500 mA. Oops, no. Resistance is 5 ohms. It would drop almost a volt across the transistor. So now you know what to avoid.)
Ok thank you so much . Let's procure the components.
 

ronv

Joined Nov 12, 2008
3,770
Ok thank you so much . Let's procure the components.
I'm not sure you will be happy with the IC. It has a hysteresis of only .045 volts, So when the battery is disconnected it's voltage may "bounce back" more than that and turn the pump on again.
 

hp1729

Joined Nov 23, 2015
2,304
I'm not sure you will be happy with the IC. It has a hysteresis of only .045 volts, So when the battery is disconnected it's voltage may "bounce back" more than that and turn the pump on again.
True. But the very fact that it kicked off says it is time to change / recharge the battery.
 

Thread Starter

mishra87

Joined Jan 17, 2016
1,034
I'm not sure you will be happy with the IC. It has a hysteresis of only .045 volts, So when the battery is disconnected it's voltage may "bounce back" more than that and turn the pump on again.
So is there any alternate to resolve this issue !!!
Because I have implemented by using Seiko battery protection IC with mosfet but failed to do that.

I want to let you know that pump is directly not connected with battery by now. It has got two switched to aspirate and dispense the liquid. The instrument ON current is only 19mA and in stand by mode it draws only 5mA and when we Aspirate or dispense the liquid pump gets ON for a time. This 4mA current fully drains the battery in stand by mode. So my purpose is to stop draining the battery below 3V by using this. If anybody having any alternate solutions please let us know.
 

ronv

Joined Nov 12, 2008
3,770
So is there any alternate to resolve this issue !!!
Because I have implemented by using Seiko battery protection IC with mosfet but failed to do that.

I want to let you know that pump is directly not connected with battery by now. It has got two switched to aspirate and dispense the liquid. The instrument ON current is only 19mA and in stand by mode it draws only 5mA and when we Aspirate or dispense the liquid pump gets ON for a time. This 4mA current fully drains the battery in stand by mode. So my purpose is to stop draining the battery below 3V by using this. If anybody having any alternate solutions please let us know.
I hope I didn't mislead you. I am under the impression that the pump runs off the same battery. Where you would see the problem is when the battery is almost down to 3 volts and the pump turned on. This will turn off the battery. When that happens the load on the battery goes away and it's voltage will go back up. It could be your controller will shut off and stay off until the battery gets down below 3 volts.
If I were to do it I would make a circuit that turned off at 3 volts and did not turn back on until the battery was charged to say 3.4 volts. I'll draw one up.
 

ronv

Joined Nov 12, 2008
3,770
So is there any alternate to resolve this issue !!!
Because I have implemented by using Seiko battery protection IC with mosfet but failed to do that.

I want to let you know that pump is directly not connected with battery by now. It has got two switched to aspirate and dispense the liquid. The instrument ON current is only 19mA and in stand by mode it draws only 5mA and when we Aspirate or dispense the liquid pump gets ON for a time. This 4mA current fully drains the battery in stand by mode. So my purpose is to stop draining the battery below 3V by using this. If anybody having any alternate solutions please let us know.
Here is an example circuit:
Different parts could be used as long ass they are low power.
 

Thread Starter

mishra87

Joined Jan 17, 2016
1,034
I
Here is an example circuit:
Different parts could be used as long ass they are low power.
I had a look of this circuit and I had calculated the cost of all part numbers as well. It was around 7-8 dollar that makes a big difference since product is already in market. So let me have this option also. I also want to know that is there any impact of battery transient while I insert with instrument to shut off this kind of devices like NCP30X or LT1495.
 

ian field

Joined Oct 27, 2012
6,536
I have NCP300 with sft1341 mosfet. I want to monitor my battery at 3V. Does attached circuit work. I have a confusion how P channel MOSFET works with NCP300. Could anybody explain me working of this circuit.

Thanks
There are logic level MOSFETs that will work at such low voltages, but the 0.7V Vb/e of a bipolar transistor gives you a lot more headroom.

Traditionally a UVLO has been a transistor with its base fed from Vcc by a Zener, add a second transistor if you need to invert the output.

There are example circuits for under voltage detectors in the TL431 programmable Zener appnotes, and its much more precise than the transistor/zener circuit.

The regular TL431 works down to 2.5V, so it should just about work for you - but I believe there is a 1.25V version, probably originally a Zetex (Ferranti) part, but probably available from various manufacturers.
 

ronv

Joined Nov 12, 2008
3,770
I

I had a look of this circuit and I had calculated the cost of all part numbers as well. It was around 7-8 dollar that makes a big difference since product is already in market. So let me have this option also. I also want to know that is there any impact of battery transient while I insert with instrument to shut off this kind of devices like NCP30X or LT1495.
Yes, the LT parts are expensive,
Have a look at NCX220GW or MCP6546.
Then MAX6006BE.
Still more expensive.
You might want to protect the FET with a diode reversed biased to ground to protect the FET from the motor if that is the transient you are speaking of.
 

ronv

Joined Nov 12, 2008
3,770
There are logic level MOSFETs that will work at such low voltages, but the 0.7V Vb/e of a bipolar transistor gives you a lot more headroom.

Traditionally a UVLO has been a transistor with its base fed from Vcc by a Zener, add a second transistor if you need to invert the output.

There are example circuits for under voltage detectors in the TL431 programmable Zener appnotes, and its much more precise than the transistor/zener circuit.

The regular TL431 works down to 2.5V, so it should just about work for you - but I believe there is a 1.25V version, probably originally a Zetex (Ferranti) part, but probably available from various manufacturers.
The TL431 circuits are neat, but the problem is the TL431 doesn't go all the way to ground. So for low voltage like this it will be really hard to get things on and off.
Edit:
Add picture
 

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ian field

Joined Oct 27, 2012
6,536
The TL431 circuits are neat, but the problem is the TL431 doesn't go all the way to ground. So for low voltage like this it will be really hard to get things on and off.
Edit:
Add picture
Since the TL431 (or 1.25V version) basically replaces the very expensive chip - it doesn't have to go all the way to ground.

There's still room for the external transistor that was there anyway that can be configured to produce the required switching swing.
 

ronv

Joined Nov 12, 2008
3,770
Since the TL431 (or 1.25V version) basically replaces the very expensive chip - it doesn't have to go all the way to ground.

There's still room for the external transistor that was there anyway that can be configured to produce the required switching swing.
Transistor. Why didn't I think of that? :oops:Only $.13 :D
 

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