I decided, if possible, to get rid of some of the shortcomings of the regulators listed above and preserve their main advantages. Let's take the principle of auto-transformation from LATR and apply it on a standard transformer by increasing the voltage above the mains voltage. I liked the transformer from the uninterruptible power supply. Basically the fact that it does not need to rewind. Everything you need is there. Transformer brand: RT-625BN.
Here is its circuit:
As can be seen from the diagram, in addition to the main winding of 220 volts, there are two more, made with the winding wire of the same diameter, and two secondary high-power ones. The secondary windings are excellent for powering the control circuit and the operation of the cooler for the power transistor.Two additional windings are connected in series with the primary winding. The photos show how this is done in colors.
We supply power to the red and black wires.
The voltage from the first winding is added.
Plus two windings. Total it turns out 280 volts. If you need more voltage, you can get more wires to fill the window of the transformer, after removing the secondary windings. Only winding must necessarily be in the same direction as the previous winding, and connect the end of the previous winding with the beginning of the next one. The turns of the winding should, as it were, continue the previous winding. If you wind up, then when you turn on the load will be a big trouble! You can increase the voltage, if only the control transistor would withstand this voltage.Transistors from imported televisions can be found up to 1500 volts, so there is plenty of space. You can take any other transformer suitable for your power, remove the secondary windings and leave the wire to the voltage you need. In this case, the control voltage can be obtained from an additional auxiliary low-power transformer for 8 - 12 volts.
If someone wants to increase the efficiency of the regulator, then you can find a way out here. The transistor is uselessly expending electricity for heating when it has to take a lot of voltage. The more you need to reduce the voltage, the stronger the heat. In the open state, heating is negligible. If you change the scheme of an autotransformer and draw a lot of conclusions on the voltage levels you need, you can apply a voltage to the transistor close to the one you need at the moment by switching the windings. Limitations in the number of transformer terminals are not available, only a switch corresponding to the number of pins is needed. The transistor in this case will be needed only for a minor accurate adjustment of the voltage and the controller efficiency will increase, and the heating of the transistor will decrease.
You can start assembling the controller. I modified the circuit from the magazine a bit, and it turned out that:
With this scheme you can significantly increase the upper voltage threshold. With the addition of an automatic cooler, the risk of overheating the control transistor has decreased. The case can be taken from the old computer power supply.
Immediately you need to figure out the order of placing the device blocks inside the case and provide for the possibility of their reliable fixing.
If there is no fuse,then you need to provide another protection against short circuit.
High-voltage terminal block securely attached to the transformer.
I put the outlet on the output to connect the load and control voltage. A voltmeter can be set to any other, at the appropriate voltage, but not less than 300 volts.
We need the details:
Cooling radiator with cooler (any).
The details can be selected based on the presence and correspondence of the nominal parameters, I put what was the first by the hand, but chose more or less suitable.
Diode Bridges VD1 - 4 - 6A - 600 V. From the TV, it seems. Or to collect from four separate diodes.
VD2 - at 2 - 3 A - 700 V.
T1 - C4460.The transistor I supplied from an imported TV set at 500V and a power dissipation of 55W. You can try any other similar high-voltage, powerful.
VD3 - 1N4007 diode at 1A 1000 V.
C1 - 470mf x 25 V, better increase the capacity.
C2 - 100n.
R1 - 1 kΩ any wirewound potentiometer, from 500 ohms and above.
R2 - 910 - 2W. Selection of base transistor current.
R3 and R4 - 1 kΩ each.
R5 is a 5 kΩ subscriber resistor.
NTC1 - 10 kΩ thermistor.
VT1 - any field effect transistor. I put the RFP50N06.
M - 12V cooler.
HL1 and HL2 - any signal LEDs, you can not put them together with damping resistors. First of all, you need to prepare a board for placing the details of the scheme and fix it in place in the case.
Place the details on the board and solder them.
When the circuit is assembled , it is time for its preliminary testing. But you need to do this very carefully. All parts are live mains. To test the device, I soldered two 220-volt light bulbs in series so that they would not burn out when 280 volts went to them. There was no equal power of light bulbs and therefore the heat of the spirals is very different. It should be borne in mind that without a load the regulator works very incorrectly. The load in this device is part of the circuit.When you first turn on better take care of your eyes (suddenly something messed up). Turn on the voltage and use a potentiometer to check the smoothness of the voltage adjustment, but not for long, to avoid overheating the transistor.
After testing, we begin to assemble a circuit for automatic operation of the cooler, depending on the temperature. I did not have a 10 kΩ thermistor, I had to take two 22 kΩ each and connect them in parallel. It turned out about ten clocks.
Fasten the thermistor near the transistor using heat-conducting paste, as for the transistor.
>img src="https://sdelaysam-svoimirukami.ru/uploads/posts/2018-06/medium/1529989155_24.jpg" style="max-width: 100%;" alt="Noiseless autotransformer with electronic voltage regulation">
Install the remaining parts and solder. Do not forget to remove the copper pads of the breadboard between the conductors, as in the photo, otherwise a high voltage may cause a short circuit in these places.