How to adjust a Buck Regulator???

[PhilipWarence]

Good day.

I have this Circuit using A8447. My output voltage is 5V.
My problem is I dont know where is(are) the divider resistor(s) to vary my output into 7.5V. Can somebody here help me how?
Also, do i need to remove the connection of Vbias and Vout if im going to target an output voltage higher than 5V?
TIA.

 

[PhilipWarence]

up

 

[Ian Rogers]

I should imagine Header 3 is for an external pot to vary the output voltage... Without the pot it is a fixed output..
But I don't know why there are three pins.. Maybe you can have three different ranges???

 

[Joe G]

the data sheet says ;

VOUT. The output voltage is adjustable from 0.8 to 24 V, set by an
external resistor divider. The voltage can be calculated with the
following formula:
VOUT = VFB × (1 + R1/R2)

 

[k7elp60]

According to the data sheet the FB or feedback voltage is very close to 0.8V. And the calculation for the R1 and R2 is expressed by Vout=VFB(1+R1/R2). Using this formula I think there is a jumper connecting pins 1 and 2 of header 3. To change the output to 7.5 volts you need to change the values of R1,R2,and R3. The formula Vout=VFB(1+R1/R2) and be transposed to:
R1=(Vout/VFB-1)R2

 

[Flyback]

Yes its the FB pin resistors...but you are better off to bring the error amplifier outside the chip , and vary the reference to the error amp than switch resistors in and out.

 

[eTech]

Hi

I don't think the schematic is correct. Here's a schematic that shows the way I think you want to configure the headers.
Also, VBIAS has a max input of 7v, so...only connect it if target output is between 3.3v-5v (as stated on the datasheet)

eT