This switching power supply works in the single switch forward topology. In the article about switching power supplies it is II.A.
Operating frequency is cca 80-90kHz. As a control circuit UC3844 is used. It is similar to the UC3842, but duty cycle is limited to less than 50%.
The transformer Tr1 was made rewinding the transformer of SMPS ATX, who also worked in the forward topology.
The primary inductance of such transformers is around 6.4 mH. The core is without air gap.
Primary is divided into two halves; Wind first half, then the other winding starting secondaries, and finally the second half.
It is also possible to use the original bottom half of the primary and not rewind it.
This power supply is suitable for power amplifiers. It has protection against short circuit and overload. The output voltage is stabilized.
Feedback is introduced through the optocoupler.
The table shows various MOSFETs rated for voltages 800 - 1000V usable as T1. For the 350W power, typical resistance in the conductive state (Rds on typ.)
should not exceed 0.8 R. MOSFETs can be connected in parallel to reduce resistance. Of course - the smaller the resistance, the better (lower conductive losses).
Voltage UDS should be 900-1000V, in worst case you can use 800V.
I also wondered about using IGBT, but you can not use those rated 600V. The 1200V ones tend to be too slow.
Experiments with IGBT BUP213 have not been successful, is has far greater losses than MOSFETs.
Very hopeful is SPP17N80C3 MOSFET with resistance only 0.25 R. Note: The data in the table may get out od date.
More appropriate MOSFETs may appear. The coming 900V IGBTs may be good.
| Type | Voltage | Current at 25°C | Resistance at 25°C | Gate capacity | Max loss at 25°C | times (ns) | Note | |||
| UDS | ID | Rdson typ. (max) | CGS | PTOT | td(on) | tr | td(off) | tf | ||
| 2SK2648 | 800V | 9A | 1,28R (1,5R) | 1200pF | 150W | 30 | 120 | 95 | 60 | salvaged from ATX |
| STW11NM80 | 800V | 11A | 0,35R (0,4R) | 1630pF | 150W | 22 | 17 | 46 | 15 | . |
| STW12NK90Z | 900V | 11A | 0,72R (0,88R) | 3500pF | 230W | 31 | 20 | 88 | 55 | salvaged from ATX |
| 2SK1363 | 900V | 8A | 1,1R (1,4R) | 1300pF | 90W | 25 | 40 | 20 | 100 | . |
| 2SK2611 | 900V | 9A | 1,1R (1,4R) | 2040pF | 150W | 25 | 60 | 20 | 95 | . |
| IRFPE50 | 800V | 7,8A | ----- (1,2R) | 3100pF | 190W | 19 | 38 | 120 | 39 | . |
| SPP17N80C3 | 800V | 17A | 0,25R (0,29R) | 2320pF | 208W | 25 | 15 | 72 | 6 | . |
| STW11NK100Z | 1000V | 8,3A | 1,1R (1,38R) | 3500pF | 230W | 27 | 18 | 98 | 55 | . |
| STW18NK80Z | 800V | 19A | 0,34R (0,38R) | 6100pF | 350W | 46 | 32 | 140 | 32 | . |
| STP10NK80Z | 800V | 9A | 0,78R (0,9R) | 2180pF | 160W | 30 | 20 | 65 | 17 | . |
| FQA7N80 | 800V | 7,2A | 1,2R (1,5R) | 1420pF | 198W | 35 | 80 | 95 | 55 | . |
| IRFBE30 | 800V | 4,1A | ----- (3R) | 1300pF | 125W | 12 | 33 | 82 | 30 | only in parallel |
| IRFPE40 | 800V | 5,4A | ----- (2R) | 1900pF | 150W | 16 | 36 | 100 | 32 | only in parallel |
| 2SK2397 | 800V | 5A | 1,7R (2,3R) | 800pF | 50W | 25 | 100 | 130 | 70 | salvaged, only in parallel |
| SPP06N80C3 | 800V | 6A | 0,78R (0,9R) | 785pF | 83W | 25 | 15 | 72 | 8 | . |
