DAC to control variable regulator output help

[Steve Sands]

I need your help in coming up with a way to convert 5 to 12 volts DC
from a DAC output to the same voltage range but at 4 amps. The
simplest way I know of is a transistor-based pass type regulator with
the DAC out going to the base. Is there a more elegant approach that I
have missed? An efficient switching regulator scheme sounds great but
all the ones I looked at use a feedback divider to set output.

Thanks for your input

Steve

 

[Fred Bloggs]

I need your help in coming up with a way to convert 5 to 12 volts DC
from a DAC output to the same voltage range but at 4 amps. The
simplest way I know of is a transistor-based pass type regulator with
the DAC out going to the base. Is there a more elegant approach that I
have missed? An efficient switching regulator scheme sounds great but
all the ones I looked at use a feedback divider to set output.

Thanks for your input

Steve

You can use a DAC to convert digital to analog current and then offset
the switcher feedback network like so- select R1 and R2 so that
(1+R1/R2)*Vref=5V, and then scale I so that digital Dmax produces Imax
so that R1 x Imax =7V. There will be duty cycle limitations for the
switcher that must be observed.

Please view in a fixed-width font such as Courier.



+---------------+
| Vout|---------+-->Vreg
| | |
| | \
| SW REG | R1 R1
| | \ Vreg= ( 1 + -- ) x Vref + I x R1
|Vref(internal) | / R2
| | |
| FB |---------+------+
+---------------+ | |
\ |
R2 | |
\ | | I
/ | |
D->I | | |
converter --- | V
+----------\ |
| \ |
| DAC >----------+
| /
+----------/

 

[Steve Sands]

You can use a DAC to convert digital to analog current and then offset
the switcher feedback network like so- select R1 and R2 so that
(1+R1/R2)*Vref=5V, and then scale I so that digital Dmax produces Imax
so that R1 x Imax =7V. There will be duty cycle limitations for the
switcher that must be observed.

Please view in a fixed-width font such as Courier.



+---------------+
| Vout|---------+-->Vreg
| | |
| | \
| SW REG | R1 R1
| | \ Vreg= ( 1 + -- ) x Vref + I x R1
|Vref(internal) | / R2
| | |
| FB |---------+------+
+---------------+ | |
\ |
R2 | |
\ | | I
/ | |
D->I | | |
converter --- | V
+----------\ |
| \ |
| DAC >----------+
| /
+----------/

Thanks so much for your time Fred. Looks ideal. I am off to the bench!

All the best to you and yours,

Steve