DC-DC converter recycling leakage inductor losses via auxiliary DC regulator
View Patent ↗A technique performed by a transformer-coupled DC-DC converter is described for recovering energy, due to leakage inductance in the transformer. A main power supply, providing a power supply voltage to a Vin terminal, is intermittently coupled to the primary winding of the transformer by a switching transistor. When the switching transistor is turned off, creating a voltage spike in the primary winding due to leakage inductance, the spike is conducted by a forward biased diode and filtered by a capacitor. The voltage at the capacitor (Vc) is then applied as an input voltage to a small pulse width modulated (PWM) regulator. The output of the PWM regulator is coupled to the Vin terminal along with the main power supply. The PWM regulator regulates the input voltage Vc to be a predetermined amount above the power supply voltage. Since the voltage spike energy is used to create the input voltage for the PWM regulator, and the output of the PWM regulator is fed back into the Vin terminal, the energy is recovered. Also, since Vc can be set to be any voltage above Vin, the voltage across the switching transistor is greatly limited.
1. A transformer-coupled DC-DC converter comprising:
a voltage input terminal for connection to a main power supply for supplying power to the converter at a first supply voltage;
a primary winding of a transformer;
a first switch controlled to intermittently conduct a current from the voltage input terminal through the primary winding, the primary winding generating a ramping current when the first switch is turned on and generating a momentary voltage pulse upon the first switch turning off;
a secondary winding of the transformer supplying a current to an output circuit for providing a DC output voltage of the converter; and
a voltage regulator receiving at a regulator input terminal an input voltage generated from the momentary voltage pulse, the regulator comprising a second switch for intermittently coupling the regulator input terminal to an output filter of the regulator, the output filter of the regulator being coupled to the voltage input terminal of the converter, the regulator controlling the input voltage to be at a regulated voltage, such that at least some of the energy in the voltage pulse is returned to the voltage input terminal and a voltage across the first switch is limited by the input voltage of the regulator, wherein
at least some of the energy in the voltage pulse is returned to the voltage input terminal upon each switching cycle of the first switch while the input voltage into the regulator is being regulated.
2. The converter of claim 1 wherein the regulator is a pulse width modulated (PWM) regulator.
3. The converter of claim 1 wherein the regulator determines a difference between a first voltage, corresponding to the input voltage of the regulator, and a second voltage, corresponding to the first supply voltage, and, in response, controls the second switch to keep the first voltage approximately matched to the second voltage.
4. The converter of claim 1 further comprising an input voltage filter connected to the voltage input terminal.
5. The converter of claim 4 wherein the output filter of the regulator includes the input voltage filter.
6. The converter of claim 1 wherein the main power supply is coupled to a center tap of the transformer, and wherein the primary winding is a first primary winding, the transformer also comprising a second primary winding, the converter further comprising a third switch controlled to intermittently conduct a current from the voltage input terminal through the second primary winding, the second primary winding generating a ramping current when the third switch is turned on and generating a momentary voltage pulse upon the third switch turning off.
7. The converter of claim 1 further comprising a first diode connected between a first end of the primary winding and the regulator input terminal, the first diode being forward biased during at least a portion of the time that the momentary voltage pulse is generated.
8. The converter of claim 7 wherein the first switch is connected to the first end of the primary winding.
9. The converter of claim 8 further comprising a capacitor filter connected to the regulator input terminal.
10. The converter of claim 1 wherein the main power supply is coupled to a center tap of the transformer, and wherein the primary winding is a first primary winding, the transformer also comprising a second primary winding, the converter further comprising:
a third switch controlled to intermittently conduct a current from the voltage input terminal through the second primary winding, the second primary winding generating a ramping current when the third switch is turned on and generating a momentary voltage pulse upon the third switch turning off;
a first diode connected between a first end of the first primary winding and the regulator input terminal, the first diode being forward biased during at least a portion of the time that the momentary voltage pulse is generated when the first switch turns off, wherein the first switch is connected to the first end of the first primary winding;
a second diode connected between a first end of the second primary winding and the regulator input terminal, the second diode being forward biased during at least a portion of the time that the momentary voltage pulse is generated when the third switch turns off, wherein the third switch is connected to the first end of the second primary winding; and
a capacitor filter connected to the regulator input terminal.
11. The converter of claim 1 further comprising a control circuit for adjusting switching of the first switch to regulate the DC output voltage of the converter.
12. The converter of claim 1 wherein the voltage regulator receives a first voltage corresponding to the input voltage of the regulator and a second voltage corresponding to the first supply voltage and controls the second switch to maintain the first voltage and the second voltage at a predetermined ratio.
13. The converter of claim 12 wherein the voltage regulator maintains the first voltage at a certain level that is higher than the second voltage to limit a maximum voltage across the first switch.
14. A method performed by a transformer-coupled DC-DC converter comprising:
supplying power from a main power supply to a voltage input terminal of the converter at a first supply voltage;
controlling a first switch connected to a primary winding of a transformer to intermittently conduct a current from the voltage input terminal through the primary winding, the primary winding generating a ramping current when the first switch is turned on and generating a momentary voltage pulse upon the first switch turning off;
supplying a current, by a secondary winding of the transformer, to an output circuit for providing a DC output voltage of the converter; and
receiving at a voltage regulator input terminal an input voltage generated from the momentary voltage pulse; and
controlling a second switch in the voltage regulator for intermittently coupling the regulator input terminal to an output filter of the regulator, the output filter of the regulator being coupled to the voltage input terminal of the converter, the second switch being controlled to cause the input voltage to be at a regulated voltage, such that at least some of the energy in the voltage pulse is returned to the voltage input terminal and a voltage across the first switch is limited by the input voltage of the regulator, wherein
at least some of the energy in the voltage pulse is returned to the voltage input terminal upon each switching cycle of the first switch while the input voltage into the regulator is being regulated.
15. The method of claim 14 further comprising the voltage regulator receiving a first voltage corresponding to the input voltage of the regulator, receiving a second voltage corresponding to the first supply voltage, and controlling the second switch to maintain the first voltage and the second voltage at a predetermined ratio.
16. The method of claim 15 wherein the output filter of the regulator includes a filter connected to the voltage input terminal.