how different Power Resistor will affect my circuits

[strameshkumar]

Hi,
I am testing DC-DC converter with (input 24V;output15V) different load resistor(330 ohm,2W; 470ohm,2W and 22ohm, 5W)). when i loaded with 330ohm resitor it takes 0.5A current. But when i connect 22 ohm 5W resitor it takes 1.7A.

Query: How the different power resistor will affect my circuit?
Does this power resistor and normal resistor will cause more current in my circuit?

Thanks,
Ramesh T

 

[(*steve*)]

Measure the voltage across the resistor when you apply it as a load.

Also use ohms law to determine the current that would flow at the full output voltage.

Then compare it with the rated output current.

It also might be that your source of 24V can't supply enough current, so measure the input voltage as well.

The only difference between a normal resistor and a "power" resistor is that someone decided to call it a "power" resistor. Presumably it can dissipate more power (and in this case it's rated at 5W rather than 2W).

 

[BobK]

A different load will definitely affect how much current is drawn by a DC-DC converter. But your currents are way out of whack.

15V into 330 Ohms is 0.68W, 0.5A at 24V is 12W, so your converter is operating at 5.6% efficiency. Something is wrong.

15V into 22 Ohms is 10.2W. 1.7A at 24 V is 40.8W. Again, efficiency is way too low.

Bob

 

[shrtrnd]

Is this a high switching frequency DC-DC converter issue?
ESR vs Frequency is a factor if your converter switching freq is above 1MHZ.