12V DC to 28V DC Converter. DC-DC Converter. Mosfets Used for Switching Transformer Primary and Secondary. No Schottky Diode Used.

The circuit described here is a DC to DC converter. The circuit uses mosfet as switching device. The secondary circuit doesn't have a Schottky diode.

The heart of the circuit is IC555 used in astable multivibrator mode. The output of IC555 is fed to primary side mosfet IRF840. The same output is fed to secondary side mosfet IRF840. Both the mosfets oscillate at same frequency of 45khz. The output is connected to a choke and a filter capacitor.

The DC DC converter presented here is tested and video is attached.

1. IC 555 1no.
2. Resistor 1K 1/4w 2 no.
3. Capacitor 0.01uF 2 no.
4. Resistor 330 ohm 1 watt 1 no.
5. Resistor 10K 1/4 w 1 no.
6. Mosfet IRF840 2 no.
7. Heatsink for mosfet 1 no.
8. Ferrite ring core id 1cm 1 no.
9. Bread board 1 no.
10. Wires 0.5 mm for wiring for transformer winding
11. 12V DC SMPS power supply 1 no.
12. Choke
13. 47uF/1000v capacitor 1no. (used as no proper component in my store)
14. 1000uF/63V is preferred.

The heart of the circuit is IC555 used in astable multivibrator mode. The output of IC555 is fed to primary side mosfet IRF840. The same output is fed to secondary side mosfet IRF840. Both the mosfets oscillate at same frequency of 45khz. The output is connected to a choke and a filter capacitor.

The drain of the mosfet is connected to a small ferrite ring core with required turns of wire both in primary and secondary. The turns and other data is explained in construction.

The output of the transformer is an AC voltage at a high frequency.

Since it is high frequency of 45khz, the size of the transformer has reduced in size and weight.

The circuit can be divided into three blocks. They are :

1. Oscillator block: This block uses IC 555 in astable multivibrator mode. The IC 555 wired as shown in the main circuit oscillates at a frequency of 45Khz.
2.  Power switch primary and secondary side: The power switches consist of mosfet IRF840. The gate of the mosfet is connected to 330ohm 1w resistor. This resistor is a current regulator. In case of mosfet short circuit or output short circuit, this resistor will limit current to mosfet gate, saving IC555 from damage.The gate of the mosfet is connected to 10K resistor to ground. This loop discharges the mosfet gate charge.
3. Ferrite transformer: This transformer is wound on a ferrite core. ID 1mm. The primary of the ferrite is 12 turns wire. Secondary of the ferrite is 20 turns wire.

The circuit is tested as shown in youtube video.