Batboard

Hi
can you tell me what is the use of load resistor in series with secondary stage switch mode power supply .

If it is a load resistor then it is normally across (parallel) the output. This is often done as some switching regulator designs need a minimum load.

If it is in series then tell us more.

sdranaweera wrote:Hi
can you tell me what is the use of load resistor in series with secondary stage switch mode power supply .

I have seen switching power supplies that generate all sorts of trash on the output with no load or minimum load. We have installed load resistors across the output in many of our installations that get rid of this trash by putting a minimum fixed load. The noise is very noticeable if the power is used in any audio stages or mic circuits.

Jim

Along the same lines as AS and Jim: if in parallel it could be to attenuate artifact and noise by providing path, or a bleeder to safely discharge the supply under no load, or as a min load to prevent the overvoltage protection from kicking in under no load; if in series it is for current limiting, or as part of the current sense circuit. Hard to say without seeing the schematic.