24VDC-1.5A power supply

[akis]

On another two thread we discussed typical SMPS units as in laptop adapters, wall plug adapters, and LED supplies. Some of them with earthed mains and some with not. Many of them connecting the negative output to the mains earth, some not. All of them using a blue Y capacitor between secondary and primary of the transformer to suppress EMI. Medical graded units use two blue capacitors in series for more safety. Many of them I have tried and they leak voltages in the outputs, both positive and negative, enough to give me jolts.

My portable device is powered by two 24VDC/1.5A supplies. Because this device is used on ones person I cannot power it with one of these SMPS without risking jolts, electrocutions and so on.

So I decided to make my own supply using a transformer and no (Chinese) SMPS.

The first problem is size and weight. Weight is most important. I used a mains toroidal 80VA, 2x18V. It *just* manages to work and it also gets hot. In order to provide some regulation I used a linear control (P-FET controlled by FET op-amp) and this gets damn hot too. The toroidal runs at 60C inside its box.

In addition there are still leaks to the earth, very small, but are there. I suspect this is to do with the capacitive coupling between primary and secondary of the toroidal.

1) Should I try to find one of the older type E-shaped transformers? Would they keep the windings apart and thus eliminate any leaks?

2) Should I try a DC-DC converter rather than the linear regulator that I use now in order to remove some heat from the box?

3) Is it at all possible to design a SMPS that will offer the advantages of low weight and less heat and also match the safety profile of the linear version?