A Circuit Used To Drive A Power Supply Or System Fan By Using Magnetizing Energy Of The Transformer
Original Publication Date: 2000-Sep-01
Included in the Prior Art Database: 2003-Jun-19
Problem: Almost all the computer power supplies use a forward topology to provide power to a computer. The load current and the magnetizing currents flow through the winding of the transformer. The load current provides the useful energy while the magnetizing energy is recycled to the primary source. The invention instead of recycling the energy back to the source uses it to drive a power supply or system fan. Circuit Description of the Prior Art: Figure 1 shows the prior art of recycling the magnetizing energy to the primary source. The circuit shows a forward converter topology to produce a regulated DC output. Here, when the transistor Q2 is turned on by a pulse width modulator (PWM), the primary energy from the source is transformed to the secondary through transformer T6. The secondary voltage developed across winding (1-4) is rectified by diode D8 and filtered by inductor L8 and capacitor C5. Also, part of the primary source energy is stored as magnetizing energy in transformer T6 when Q2 is on. When Q2 is turned off, voltage across winding (1-4) is reversed and the D8 turns off and the current through inductor L8 will continue to flow through diode D10. Also when Q2 turns off, voltage across winding (5-6) is reversed and the diode D7 is turned on and the stored magnetizing energy is cycled back to the primary input source. If this provision is not made, the transformer T6 will saturate because it’s core needs to be reset every switching cycle. This energy has to be recycled at very high frequency without being utilized and therefore results in power dissipation.