PIC self supply measurement

[rc-pilot-freak]

No and yes. But I solved the problem. Since my supply is going to be above 5V (which is always regulated through the 5V LDO) i will get 5V on PIC. But when my supply drops under 5V and keeps droping as the battery supply runs out, i need stable refernece on PIC's Vref pin.

I've done this with LM336-2.5V reference diode.

So all the time I know that the reference is 2.5V even if the supply voltage changes. Now i can do an A/D to measure the supply voltage.

[Acetronics2]

Hi,

For My R/C systems, I only need to know if batt is under 4v4 ...

at 4.65v, there's the MC33064P5 from motorola ( µChip equivalents exist ...)

It's a TO92 case ... and output is open collector, low for lowbatt.

The MC 33164P5 ... has a 4.3v trip point.

Moreover you can add as much hysteresis as you want adding a couple of resistors

sooooooo simple to check a low input state ... rather than use an ADC !!!

Alain

[rc-pilot-freak]

Thanks Acetronics for pointing that chip to me. It is very usefull in battery supplied circuit. I will order my self a few pieces to test with.

Now i'm stuck at a different problem.

I was using the PWM interrupt routine from Curtis Parrott, which he published here, to drive the Mosfet (the load needs 4Amps at 1.3Volts). http://www.picbasic.org/forum/showthread.php?t=5316

When I raise the voltage to 2.6V the mosfet starts heating very quickly. I don't know where the problem is. Am I using to high frequency?

[Joe Rocci]

What is the part number of the FET you're using?

[sayzer]

...

When I raise the voltage to 2.6V the mosfet starts heating very quickly. ...

Why don't you post the schematic?

Let us see how you drive the Mosfet(s).

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[Acetronics2]

I was using the PWM interrupt routine from Curtis Parrott, which he published here, to drive the Mosfet (the load needs 4Amps at 1.3Volts). http://www.picbasic.org/forum/showthread.php?t=5316

Buuuuuut, it's the OTHER Forum ... isn't it ???

When I raise the voltage to 2.6V the mosfet starts heating very quickly. I don't know where the problem is. Am I using to high frequency?

P= U^2 / Z ...

You just have to dissipate 4 Times than with 1.3v !!! ... if the load is unchanged.

the IRFZ is given for 18 mOhms,

18E-3*4*4 = .3 watts

18E-3*8*8 = 1.15 watts ... @62.5°C/W ... 72°C Temp Raise

Your fingertip is burnt !!!

That's for continuous conduction ...


With PWM, you have to charge and discharge 1.5nF @ your PWM rate ...

first verify if it is possible from the Pic pin ... unless the Mosfet won't "saturate" and ... overheats.

Second, verify switching conditions with the calculator you will find on ... the Web (I do not remember !!! , but it's one of the greatests Mosfets manufacturer's site )

Alain

Now, using Power switching close to R/C systems ....especially aboard planes ... looks like "Kamikaze" Philosophy.

my opinion ... widely shared in the National Scale Team !!!