Active diode not allowing full voltage through

Question

I'm working on a transformer active battery balancing circuit and have it working except, due to the diode voltage drop on the secondary, I need an alternative.

Since the battery cell voltage is 4 V, a 1 V drop is 25% efficiency loss and obviously will have huge imbalance issues. I thought about adding another winding on the transformer to increase the voltage but would instead like to add a active diode.

I tried the following circuit design but it's not working. The IGBT is not turning on fully and only allowing 1.5 V through. I am using a RJP30E2 which has a saturation voltage of 1.7 V. The transformer is running at 120 kHz.

I have very little experience and understanding of electronics and started this project a few weeks ago.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

Although 15 A is a lot of current for a logic-level MOSFET, all hope is not lost.

Take, for instance, a DMN2011. Let's look at the datasheet.

First things first, lets check out the Electrical Characteristics on Page 2 and see what the "On Characteristics" looks like. We want to scrutinize the "Static Drain-to-Source On-Resistance":

This is looking promising! Let's investigate further.

On page 3, figures 1 and 3:

Figure 1 shows us that current is pretty linear with voltage at 15 A with Vgs of 1.8 V and higher.

Figure 3 shows us that the drain to source resistance at Vgs of 2.5 V and 15 A is only about 0.009 Ω. Nine Milliohm!

Using Ohm's law, 15 A over 9 mΩ drops only 0.135 V.

Depending on your other requirements, something like this could work.