Need help in desiging 16V to 9V step down regulator circuit

[o0tsubasa0o]

Hi im new to robotics and circuit . I have a project to remodify a circuit for the pervious robot into a 16.8V 4 cell battery to 9V output .


The top part of the picture is the old circuit for robot . 4 cell 16v battery to the motor driver card . 2 cell 8v battery to the mico controller chip .

The bottom part is my project , my objective is to remodify the first part of the circuit . 4cell [ 16V ] power sourice to motor and also pass through a step down regulator to the micro controller chip (output 9V ) .

i need help with designing a step down regulator circuit diagram for the 16V 4 cell battery to -> a step down regulator to -> micro controller card .

The regulator is Traco Power -> TSR 1-2490  http://singapore.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6664376

Please help me thx .

[BEAMer]

If you are using it to power a microcontroller, then you don't necessarily require a switching regulator. A linear regulator will do. LM7809 is more than sufficient. Read the datasheet of this regulator.

BEAMer

[o0tsubasa0o]

erm my project supervioser said i cant use linear , so i can only use a step down regulator . anyone can help me with the circuit diagrm ? thx

[billhowl]

Here is the circuit diagram.

[Soeren]

Hi,

(output 9V ) .

If the robot has got an on-board (linear) voltage regulator to go from 9V to 5V, you could remove that and select a switcher with 5V output instead. That would increase the overall efficiency.

[o0tsubasa0o]

to:billhowl  thx for ur ciruit diagram .

thx for the advices i will try them out .

[o0tsubasa0o]

er can anyone help me with joining the regulator diagram together with the motor to form 1 circuit diagram . thx

regulator circuit diagram ->


and can anyone tell me why do i use a 47uF 25V capcitor in the regulator circuit ?

[Soeren]

Hi,

er can anyone help me with joining the regulator diagram together with the motor to form 1 circuit diagram . thx

This should do

and can anyone tell me why do i use a 47uF 25V capcitor in the regulator circuit ?

According to the datasheet, for input voltages of 32V and beyond, a 22µF cap is needed, but nothing is described for less than 32V.
However, it's a good idea to have a cap in front of a voltage regulator and more so when it's a switcher taking its power in pulses, as the battery might not be able to cope and the resistance of the leads from the battery will come more into play without it.

Normally, you'd have a cap on the output as well, but since I don't know what you're gonna load it with and since it has a limit of 470µF capacitive load, I haven't included one, but if you haven't got any capacity in the load, add between 10µF and 50µF as close to the output terminal as possible (to the ground plane), as this will reduce the output ripple (which can be up to 75mV in amplitude without a cap).

With a switcher (and anything that's electrically noisy), the capacitor should have the lowest possible ESR (Equivalent Series Resistance) and using 2 or 3 to sum up to the needed value gives a lower ESR (since each ones ESR is parallelled with the rest).

The coil L1 can be just about any coil with a good wrap of wire, the best will be powdered iron cores (yellow core) that you can find in abundance in broken PC power supplies. If you cannot find one, just use a piece of wire and live with the motor (electrical) noise remaining.

[o0tsubasa0o]

thx for helping me to understand ,i would like to know which capacitor do i need to use for the ouput, the output is connected to a 8051 microcontroller board .

[Soeren]

Hi,


If you use regular (wet) electrolytics, something between 20µF and 200µF should do - as before, if you 2 or 3 lesser ones, ESR and ripple will be lower.

[o0tsubasa0o]

thx