I have a confusion regarding the current mode control of the DC-DC converters. I have seen that in such a mode we have to add the inductor current wave with the external ramp As I have read in the datasheet of the UC3842.



Now in case I am using an IC having a full bridge configuration then how will I implement the current sense mode in that? In that case, I would have both the positive and the negative currents, how would they be separated for the current sense mode?
Secondly, the datasheet of UCC3842 shows that we can use the current sense mode in the way below in the full bridge but I am not able to understand the the diode eliminated the negative half cycle and how the current sense works in this case.


Kindly help me with this. I shall be very thankful

 

You can use a very similar current sense scheme to the UC3842 by putting the current sense resistor between ground and the junction of the sources of the low-side transistors.

 

You can use a very similar current sense scheme to the UC3842 by putting the current sense resistor between ground and the junction of the sources of the low-side transistors.

I mean to say why if the diode is used then the nagitive cycle would be showing zero voltage and we would have a ramp that have zeros in between. Comparing this would still give results?? How?

 

The current transformer (CT) has a burden resistor (Rs) that converts the secondary current to a voltage. There is no negative current as such, the primary current is the DC feed to the bridge, so is a varying current with a DC average offset but the transformer removes the offset so the output of the CT is centred on zero. The diode effectively removes the DC Bias leaving a time varying dc voltage that mirrors the averaged current in the bridge, filtered by the subsequent RC network.