Voltage Regulator Vs Dc To Dc Converters

 
#1

My Antonn project is having a power problem which I hope someone can help me with. I am supplying the controls with 12vdc and 5vdc from an old computer power supply. (The 5vdc runs the Io Tiny and servos which works fine.)( 12vdc runs a remote controller board.) I have two more power requirements. I require 7.2 vdc and 3.8 - 4.0 vdc power. The 7.2 vdc supplies a Scary Terry Audio Board and the current shouldn't exceed about 500 ma. The other device uses 3.8 to 4.0 vdc at about 150ma. There was no data on the smaller device, so I need to guess. (origionally ran off of a LiPo battery.)

I purchased a DC to DC converter able to supply the correct voltages and currents from the 12vdc and 5vdc supply I have available. I wired up the converters, set the proper voltages, but the converter fails to work with either device. I assume the converter supplies a type of PWM DC power. The units seem unable to tolerate the pulsing.

I have a limited electronic knowledge. I need to figure out how to build two regulated supplies, one able to supply 7.2 vdc from 12 vdc and the other 4 vdc from a 5 volt supply. Can anyone help?

#2

Andy,

You don't need to build one, there are plenty of adjustable voltage regulators:

I would recommend 2 x https://www.pololu.com/product/2103

connect both to 12V power source, using a voltmeter you can adjust the trimmer pot to the required output voltage.

Quote:



input voltage: 4.5 V to 42 V (note: the input voltage should be at least a few volts above the output voltage)

output adjustable from 2.5 V to 7.5 V (D24VxALV).

The output voltage is set using the board’s trimmer potentiometer

maximum output current of 600 mA (D24V6Axx)

#3

Hello @ptp,

Thanks for the info but, this is very similar to what I have. I believe the output is PWM not pure DC so my audio board doesn't work. The output voltage setting is set correctly at 7.2 vdc. The converter current is not exceeded.

I know the audio board is fine because when I hook up the in the wall supply it works.

My goal is not to have 4 different power supply wires coming into the robot from 4 different source. (I tried a second unit with the same results. Bought 4)

#4

can you post a picture of your regulator ?

#5
#6

Sorry for the delay. I cheated the 4 vdc. I put a diode in series from the 5 vdc supply and got it to 4.10 vdc. Next I need 7.2 / 7.4 vdc. From 12 vdc. I will post the converter picture when I get home. Thanks for your efforts..

#7

This is the Dc-Dc Converter

Input 3.2 to 40 v
Output 1.25 to 35 v
Current (MAX) 3A
Switching Hz 150kHz
Ripple 30mV(MAX)


User-inserted image

I won't work with my application.

I installed it in Antonn, now I will have to cut it out and try something else. There must be a 12V to 7.2V Regulator. I got to look around.

I eliminated the 4 volt problem so that problem is gone.

I am concerned with switching regulators.

#8

Hi @ptp,

Any advice on using a LM7908?

#9

Andy,

I never used that one, but the L7805 (5v) is well known, i still use them...
is very simple to interface you need only In, GND, out.

You should add some capacitors to remove any oscillation/noise.

*** Note:

You want the LM7808 (positive version) not the LM7908 (negative version)

*** Specs:

https://www.fairchildsemi.com/datasheets/LM/LM7808.pdf

Typical Application (page 18)
2 ceramic capacitors 0.33 uf and 0.1 uf

#10

WOW,,, Now I am in trouble.
I was told to try the talk servo which if it works may eliminate using this board altogether. I still have the need for 12vdc to 7.2 to 8 vdc on another project so your help will not be wasted. I will be ordering a couple of LM 7808 s soon no mater if the talk servo works or not.

Thanks for the help and info. (The cap data is really helpful.)