switching voltage regulator problem!!

[oztug]

i use lm2675-adj SIMPLE SWITCHER Power Converter High Efficiency 1A
Step-Down Voltage Regulator with components Cin=33uf,Cout=47uf,L=100uh
and Cb=100uf .
I observe that the output voltage is straight line at 5,30 volt with
no load on the oscilator screen .And then i connect 7.8 ohm resistor
to output . A distortion become after i load 7,8 ohm resistor. The
output voltage picture is at this link.
http://www.geocities.com/oztug1/electronics/lm2675adj_output.jpg
Why does it occur? and how can i make a straight output voltage?

 

[Frank Bemelman]

i use lm2675-adj SIMPLE SWITCHER Power Converter High Efficiency 1A
Step-Down Voltage Regulator with components Cin=33uf,Cout=47uf,L=100uh
and Cb=100uf .
I observe that the output voltage is straight line at 5,30 volt with
no load on the oscilator screen .And then i connect 7.8 ohm resistor
to output . A distortion become after i load 7,8 ohm resistor. The
output voltage picture is at this link.
http://www.geocities.com/oztug1/electronics/lm2675adj_output.jpg
Why does it occur? and how can i make a straight output voltage?

You could try a lower-esr capacitor. Or a larger one; small value
capacitors tend to have higher esr values.

 

[Boris Mohar]

i use lm2675-adj SIMPLE SWITCHER Power Converter High Efficiency 1A
Step-Down Voltage Regulator with components Cin=33uf,Cout=47uf,L=100uh
and Cb=100uf .
I observe that the output voltage is straight line at 5,30 volt with
no load on the oscilator screen .And then i connect 7.8 ohm resistor
to output . A distortion become after i load 7,8 ohm resistor. The
output voltage picture is at this link.
http://www.geocities.com/oztug1/electronics/lm2675adj_output.jpg
Why does it occur? and how can i make a straight output voltage?

Larger value low ESR capacitor. Short leads in the switching/filter path.
How does the Vin look?



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/

void _-void-_ in the obvious place

 

[John Popelish]

i use lm2675-adj SIMPLE SWITCHER Power Converter High Efficiency 1A
Step-Down Voltage Regulator with components Cin=33uf,Cout=47uf,L=100uh
and Cb=100uf .
I observe that the output voltage is straight line at 5,30 volt with
no load on the oscilator screen .And then i connect 7.8 ohm resistor
to output . A distortion become after i load 7,8 ohm resistor. The
output voltage picture is at this link.
http://www.geocities.com/oztug1/electronics/lm2675adj_output.jpg
Why does it occur?

The converter produces pulses that are filtered by the inductor and
output capacitor. Such a filter cannot produce pure DC. there must
always be some trace of the pulse evident in the output.

and how can i make a straight output voltage?

You can't. You can only alter the filter (lower shunt capacitance
across the inductor, lower ESR capacitor, increased inductance and or
capacitance in the filter, etc.). The exact layout of the switcher
and filter components also affects how the small inductive and
resistive drops of the conductors add to the output or not. This
means that all the ground connections must be a star ground, with the
input and output capacitors connected directly to the anode of the
schottky diode with as short as possible connections.

 

[yigiter]

what is your workspace? if you use a breadboard to try it, breadboard may
cause some problems. so if you use a breadboard, you could try a PCB with
enough track widths. Also you can use the link below for professional
help.

http://wwwd.national.com/national/PowerMB.nsf

Erkan YİĞİTER

 

[yigiter]

what is your workspace? if you use a breadboard to try it, breadboard may
cause some problems. so if you use a breadboard, you could try a PCB with
enough track widths. Also you can use the link below for professional
help.

http://wwwd.national.com/national/PowerMB.nsf