I have made a simple buck converter that gives me a clean output of 5v when I have a load of 391 ohms, however if I reduce the load to say 5 ohms it gives me no more than 380mV on the the output. Does anybody know why this may be?

 

I have made a simple buck converter that gives me a clean output of 5v when I have a load of 391 ohms, however if I reduce the load to say 5 ohms it gives me no more than 380mV on the the output. Does anybody know why this may be?

Maybe you could post a schematic of what you have.

 

Post you schematic and what coil you use.

 

A low-ohm resistor is actually called a "heavy" load, by the way.

If you are using a commercial circuit, it could be that the circuit is going into shutdown and protecting itself from overcurrent.

If the circuit is your own design, it could be that you are not able to maintain a high enough duty cycle to generate a 5-volt output at 1 amp. Or it could be that your method of sensing the output voltage is flawed. The output could have 5-volt spikes, but an average voltage of 0.38 volt, for example. If you have unintentionally built a peak detector for your feedback circuit, that could explain what is going on. Try increasing the output capacitance.

Can you post a schematic? Even a hand drawn one helps tremendously in diagnosing your issue.

Also, check your input source. For example, if the input to your circuit is a 9-volt battery, the battery is simply not capable of delivering that kind of current. When you put the 5 ohm resistor on the output of the converter, does the input drop to an abnormally low voltage, too?