Mosfet stable Volt out

[jetpr]

MosFet out volt

i need help how stable Volt out with PWM and MosFet

the out put is up and down for one volt

example: v1.0
v1.1
v1.0

Bat: 7.2v souce

[mister_e]

HEIN.. have you some schematic and/or more details of your stuff ???

I really try to understand but... not sure enough to provide a good answer to that.

Try to tell us what you really expected as output swing... can i understand you want from 0 - 1 Volt or a 0.1 volt steps with a 7.2V battery as power source???

if i'm right... if not please somebody slap me

7.2 / 256 = 0,028125 volts by 8 bit PWM definition duty step

to get 0.1 volt: duty = 0.1/0.02823529 = 3.55555 = 3 or 4 test it

to get 1 volt : duty = 1/0.02823529 = 35.5555 = 35 or 36 test it

to get 1.1 volt: duty = 1.1/0.02823529 = 39.1111 = 39

[jetpr]

I am driving a dc motor with MosFet and when i read the volt out clamp to the motor is up and down so me robot a fast and slow ...

Example : out v is shut be 2.0 and not 2.1 but after liter of time change to 2.1 so my robot run i liter fast for a second and then go back so is not stable

my source is 7.2v


my MOSFET is Rectifier IRLU3103
I use 10K resistor, with a 12K resistor gate to ground. Higher gate to ground

resistance reduces resolution of the byte Duty Cycle variable.

[mister_e]

mmm, in all my motor speed control, i read the voltage on the motor with an A/D input of the PIC. Kinda feedback control.

Once you have the voltage reading from the motor, simply monitor it and do the according change in your PWM statement or routine.

10K in serie look a bit high... is 220 Ohms to 1K do the same with the same pull down on the gate?

May be a stupid question but, is your PIC output is an open drain?!? RA4 ???

[jetpr]

Hi ken you send schematic or some help who i made that...

my pic is pic18f252 and i conect to the pwm pin with 2 res. one to ground and the other to the gate in the same line like a volt divider..

my code

MotorDC VAR CCPR1L
MotorOut VAR PORTC.2
MotorOn CON %1111110 '16 Pre/Scale
MotorOff CON %1111010
MotorEnable VAR T2CON

PumpDcSet=15
CurrentStep = 0 to 100 of rc pulse
MotorScaleFactor = 255 - 15
MotorScaleFactor / CurrentStep

MotorDC = MotorScaleFactor / 100 * CurrentStep + PumpDcSet

Pause PauseScalefactor * 1000 / MotorScaleFactor Factor

[mister_e]

here's something to play with

' PIC18F2220 
DEFINE OSC 20

TRISC = 0 ' PORTC as output
TRISA = 3 ' RA0 & RA1 as input

PR2=$FF ' load frequency period (PWM freq=1.2 KHZ)

ADCON1 = %00001101 ' Set RA0 & RA1 as analog
ADCON2 = %10000110 ' Right justified result
                   ' Fosc/64
                   ' Tad = 0
                   
ADCON0.0 = 1       ' enable a/d

TMR2DutyVar     var word
AdResult        var word
Voltage         var word
Source          var word
SelectedVoltage var word
Quanta          con 125 ' (5Volt/1024)*256=0.125 = 125

SelectedVoltage = 110 ' mean 1.1 volt
tmr2dutyvar = 156 ' according duty to get 1.1Volt = (1.1/7.2)*1024

Start:
    gosub InitPWM
    
    ' Read Motor voltage supply line
    ' ------------------------------
    '
    ADCON0 = %00000101 'select channel 1 
    pauseus 100
    ADCON0.1 = 1 'start conversion
    while ADCON0.1 ' wait for end of conversion
    wend   
    Adresult.highbyte = ADRESH
    adresult.lowbyte = ADRESL
    Source = (adresult */ quanta )
    Source = source * 288 ' to have a range of 7.2volt
    Source = div32 100 

    ' Read feedback motor voltage
    ' ---------------------------
    '
    ADCON0 = %00000001 ' select channel 0
    pauseus 100
    ADCON0.1 = 1
    while ADCON0.1 ' wait for end of conversion
    wend   
    Adresult.highbyte = ADRESH
    adresult.lowbyte = ADRESL
    voltage = (adresult */ quanta )
    voltage = voltage * 144 ' to have 7.2V range
    voltage = div32 100     
    voltage = source - voltage 

    ' Voltage regulation
    ' ------------------
    '
    if voltage < selectedvoltage then 
       if tmr2dutyvar < 1023 then TMR2DutyVar=TMR2DutyVar+1
       gosub initpwm
    endif

    if voltage>Selectedvoltage then
       if tmr2dutyvar then TMR2DutyVar=TMR2DutyVar-1
       gosub initpwm
    endif
    goto start


InitPWM:
    'set Duty cycle
    CCP1CON.5=Tmr2dutyvar.1
    CCP1CON.4=Tmr2dutyvar.0
    CCPR1L =(tmr2dutyvar>>2)
    
    T2CON=%00000110 ' start timer 2
                    ' set prescaler = 16

    CCP1CON = %00001100 ' pwm mode for CCP1
    return

[jetpr]

Hi thanks for the help...

Hi what type of software do you use for draw the Schematics ...

[mister_e]

Hi jetpr, I use P-CAD. I heard also some good comment on something called EAGLE.