USRE38196EExpiredUtility
Control of stored magnetic energy in power converter transformers
Est. expiryJan 17, 2015(expired)· nominal 20-yr term from priority
H02M 3/33569H02M 1/346H02M 1/0009H02M 1/34Y02B70/10H02M 3/33507
81
PatentIndex Score
34
Cited by
192
References
144
Claims
Abstract
Apparatus (and a method) useful in a switching power converter having a transformer and a primary switch for connecting a DC input source to a primary winding of the transformer during a portion of each of a succession of converter operating cycles, the apparatus includes a reset capacitor and a reset switch. Reset circuitry cooperates with the reset switch to connect and disconnect the reset capacitor in a manner which provides for resetting the transformer and which allows a current having a non-zero average value to flow in the reset switch. Another aspect is a method for limiting the slew rate in a switching power converter which includes a transformer and a reset circuit of the kind which non-dissipatively recycles the magnetizing energy stored in a transformer during each of a succession of converter operating cycles. The method includes sensing the magnetizing current which is flowing in said transformer, and allowing initiation of another converter operating cycle only if the magnetizing current meets a predefined criterion for safe converter operation. In embodiments of the invention the predefined criterion may be the magnetizing current passing through a predefined value, e.g., zero.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1. A method for limiting the slew rate in a switching power converter which includes a transformer and a reset circuit of the kind which non-dissipatively recycles the magnetizing energy stored in a transformer during each of a succession of converter operating cycles, said method comprising
sensing the magnetizing current which is flowing in said transformer, and
allowing initiation of another converter operating cycle only if the magnetizing current meets a predefined criterion for converter operation.
2. The method of claim 1 wherein said predefined criterion comprises the magnetizing current passing through a predefined value.
3. The method of claim 1 wherein said predefined criterion comprises the magnetizing current crossing through zero.
4. Apparatus for use in a switching power converter of the kind which delivers power from a DC input source to a load via a transformer and which has a primary switch for connecting said DC input source to a primary winding of said transformer during a portion of each of a succession of converter operating cycles, said apparatus comprising:
reset circuitry including
a capacitor leg;
a series circuit connected between said capacitor leg and said transformer, said series circuit providing the only substantial path for completing a circuit comprising said capacitor leg and said transformer;
said series circuit comprising switch circuitry which enables current flow between said capacitor leg and said transformer through said series circuit during a closed state and inhibits current flow between said capacitor leg and said transformer through said series circuit during an open state; and
additional circuitry connected to said capacitor leg which allows a current having a non-zero average value to flow in said series circuit;
said reset circuitry resets said transformer by transferring energy stored in said transformer to said capacitor leg and back to said transformer without returning energy to said DC input source.
5. The apparatus of claim 4 wherein said switch circuitry enters said open and said closed states at times based on switching of said primary switch.
6. The apparatus of claim 4 wherein said switch circuitry is connected in series with said capacitor leg.
7. The apparatus of claim 4 wherein said additional circuitry includes circuit elements connected to allow magnetizing energy to be transferred between said transformer and said capacitor leg only if the voltage across said capacitor leg is of a particular polarity.
8. The apparatus of claim 4 wherein said additional circuitry includes circuit elements connected to inhibit bidirectional energy flow between said capacitor leg and said transformer.
9. The apparatus of claim 4 connected across a winding of said transformer.
10. The apparatus of claim 9 wherein said winding comprises said primary winding.
11. The apparatus of claim 9 wherein said winding comprises a secondary winding.
12. The apparatus of claim 9 wherein said winding comprises an auxiliary winding.
13. The apparatus of claim 4 wherein said switch circuitry comprises a unidirectional switch connected in parallel with a unidirectional conducting element, said unidirectional switch and said unidirectional conducting element being arranged to conduct in opposite directions.
14. The apparatus of claim 13 wherein said unidirectional switch comprises a MOSFET.
15. The apparatus of claim 14 wherein said unidirectional conducting element comprises the intrinsic body diode of said MOSFET.
16. The apparatus of claim 13 wherein said unidirectional switch comprises a MOSFET in series with a series diode, said series diode and said MOSFET being poled to conduct in the same direction.
17. The apparatus of claim 7 or 8 wherein said circuit elements comprise a reset diode connected in parallel with said capacitor leg.
18. The apparatus of claim 8 wherein said bidirectional energy flow is allowed only if the voltage across said capacitor leg is of a particular polarity.
19. The apparatus of claim 7 or 8 wherein said particular polarity is that which will result in a reversal in the polarity of transformer magnetizing current during said closed state.
20. The apparatus of claim 16 wherein said additional circuitry includes circuit elements which inhibit bidirectional energy flow between said capacitor leg and said transformer and wherein said circuit elements comprise a reset diode connected across a series circuit comprising said reset capacitor and said series diode.
21. The apparatus of claim 4 wherein said switching power converter comprises a forward power converter.
22. The apparatus of claim 4 wherein said switching power converter comprises a zero-current switching converter.
23. The apparatus of claim 4 wherein said switching power converter comprises a PWM converter.
24. The apparatus of claim 4 wherein said switch circuitry enters said open state prior to the ON period of said primary switch.
25. The apparatus of claim 4 wherein said switch circuitry enters said closed state during the OFF period of said primary switch.
26. The apparatus of claim 4 wherein said switch circuitry remains in said open state throughout the ON period of said primary switch.
27. The apparatus of claim 4 wherein said primary switch connects said DC input source to said primary winding essentially coincidentally with said switch circuitry entering said open state.
28. The apparatus of claim 4 wherein said primary switch connects said DC input source to said primary winding a finite delay after said switch circuitry enters said open state.
29. The apparatus of claim 28 wherein said finite delay accommodates charging and discharging of capacitances in said converter.
30. The apparatus of claim 29 wherein said capacitances comprise parasitic capacitances.
31. The apparatus of claim 29 wherein said capacitances are associated with said primary switch.
32. The apparatus of claim 29 wherein said capacitances are associated with said switch circuitry.
33. The apparatus of claim 29 wherein said capacitances are associated with windings in said transformer.
34. The apparatus of claim 4 further comprising:
slew control circuitry for inhibiting initiation of a converter operating cycle based upon the value of a magnetizing current in said transformer.
35. Apparatus for use in a switching power converter of the kind having a transformer for transferring energy from a DC input source to a load during a forward energy transfer portion of a succession of converter operating cycles, and a primary switch for connecting said DC input source to a primary winding of said transformer during said forward energy transfer portions, the apparatus comprising:
a reset capacitor;
a series circuit connected between said reset capacitor and said transformer, said series circuit providing the only substantial path for completing a circuit comprising said reset capacitor and said transformer;
said series circuit comprising a reset switch; and
reset circuitry which cooperates with said series circuit to connect and disconnect said reset capacitor in a manner which
provides for resetting a core of said transformer, and
allows a current having a non-zero average value to flow in said series circuit,
said reset circuitry including a reset diode connected in parallel with said reset capacitor to inhibit polarity reversal of the voltage across said capacitor.
36. A reset method for use in a switching power converter of the kind having
a transformer,
a primary switch for connecting a DC input source to a winding of the transformer during a portion of each of a succession of converter operating cycles,
a reset capacitor, and
a series circuit connected between said reset capacitor and said transformer, said series circuit providing the only substantial path for completing a circuit comprising said reset capacitor and said transformer;
said series circuit comprising a reset switch which enables current flow between said reset capacitor and said transformer through said series circuit in a closed state and inhibits current flow between said reset capacitor and said transformer through said series circuit in an open state,
said method comprising connecting and disconnecting said reset capacitor in a manner which provides for resetting said transformer and which allows a current having a non-zero average value to flow in said series circuit.
37. The method of claim 36 wherein the operation of said primary switch occurs substantially coincident with disconnecting said reset capacitor.
38. The method of claim 36 wherein the operation of said primary switch occurs a finite delay after said reset capacitor is disconnected.
39. Switching power converter apparatus comprising:
a DC input source;
a transformer having a primary winding;
a primary switch for connecting said DC input source to said primary winding during a portion of each of a succession of converter operating cycles;
a reset capacitor;
a series circuit connected between said reset capacitor and said transformer, said series circuit providing the only substantial path for completing a circuit comprising said capacitor leg and said transformer;
said series circuit comprising a reset switch; and
reset circuitry, including a reset diode connected in parallel with said reset capacitor to inhibit polarity reversal of the charge stored by said capacitor, said reset circuitry cooperating with said reset switch to connect and disconnect said reset capacitor in a manner which provides for resetting a core of said transformer, and allows a current having a non-zero average value to flow in said series circuit.
40. A power supply method comprising the steps of:
initiating energy transfer from a DC input source to a load via a transformer by connecting said DC input source to a winding of said transformer during a forward energy transfer portion of each of a succession of converter operating cycles;
resetting said transformer during each of said converter cycles by providing for energy transfer between said transformer and a reset capacitor during a second portion of said converter operating cycles such that the flux in the transformer is reversed; and
selectively shunting said reset capacitor to prevent polarity reversal of the voltage across said reset capacitor.
41. The method of claim 40 wherein the initiation of said step of initiating energy transfer essentially coincides with completion of a previous said step of resetting said transformer.
42. The method of claim 40 further comprising the step of imposing a finite delay after performing said step of resetting said transformer and before commencing said step of initiating energy transfer.
43. The method of claims 38 or 42 wherein said finite delay accommodates charging and discharging of capacitances.
44. The method of claim 43 wherein said capacitances comprise parasitic capacitances.
45. The method of claim 44 wherein said capacitances are associated with at least one switch.
46. The method of claim 44 wherein said capacitances are associated with at least one winding of said transformer.
47. The method of claim 1 wherein the sensing further comprises sensing magnetizing current flowing between a winding of the transformer and a reset capacitor.
48. The method of claim 47 wherein the sensing further comprises providing an impedance between the winding of transformer and the reset capacitor and sensing the voltage induced in the impedance by the magnetizing current.
49. The method of claim 48 wherein the impedance is a resistor.
50. The method of claim 48 further comprising a first unidirectional conducting device in series with the impedance.
51. The method of claim 47 wherein the sensing further comprises sensing a voltage across a first unidirectional conducting device connected between the winding of the transformer and the reset capacitor.
52. The method of claim 51 wherein the sensing further comprises:
providing a source of bias current, connected through a second unidirectional conducting device to the reset capacitor side of the first unidirectional conducting device, the bias current and second unidirectional conducting device being poled to reverse bias the first unidirectional conducting device; and
sensing the voltage, Vs, across the series combination of the first and second unidirectional conducting devices.
53. The method of claim 52 wherein the second unidirectional conducting device comprises a diode.
54. The method of claim 53 wherein the source of bias current further comprises a voltage source, Vb, and a current limiting resistor.
55. The method of claim 52 wherein the sensing further comprises detecting a value of Vs corresponding to when the magnetizing current crosses zero.
56. The method of claim 55 further comprising inhibiting initiation of another converter operating cycle until Vs indicates that the magnetizing current crosses zero.
57. The method of claim 55 further comprising inhibiting initiation of another converter operating cycle until Vs indicates that the magnetizing current has passed through a predefined value.
58. The method of claim 52 further comprising providing a signal indicating that a primary switch has entered an OFF state.
59. The method of claim 58
further comprising sensing current flowing in a primary - switch diode connected in parallel across a primary switch and poled to block current flow from a DC input source to a primary winding of the transformer; and
turning on the primary switch after a current flows through the primary - switch diode indicating that capacitances associated with the primary switch have discharged.
60. The apparatus of claim 4 further comprising,
a sense circuit connected to the series circuit for detecting completion of a forward energy transfer portion of the converter operating cycles.
61. The apparatus of claim 60 wherein the sense circuit senses magnetizing current flowing between the transformer and the capacitor leg.
62. The apparatus of claim 61 wherein:
the series circuit further comprises a first unidirectional conducting device poled to conduct a magnetizing current during a first portion of a magnetizing energy recycling portion of each of the succession of the converter operating cycles; and
the sense circuit sense the current flowing in the first unidirectional conducting device.
63. The apparatus of claim 62 wherein:
the series circuit further comprises an impedance connected in series with the first unidirectional conducting device and the sense circuit senses a voltage across the impedance induced by the magnetizing current.
64. The apparatus of claim 63 wherein the impedance comprises a resistor.
65. The apparatus of claim 63 wherein the first unidirectional conducting device comprises a diode.
66. The apparatus of claim 62 wherein the sense circuit senses a voltage across the first unidirectional conducting device.
67. The apparatus of claim 66 wherein the sense circuit further comprises:
a source of bias current connected through a second unidirectional conducting device to the capacitor leg side of the first unidirectional conducting device, the bias current and second unidirectional conducting device being poled to reverse bias the first unidirectional conducting device; and
the sense circuit senses the voltage, Vs, across the series combination of the first and second unidirectional conducting devices.
68. The apparatus of claim 67 wherein the second unidirectional conducting device comprises a diode.
69. The apparatus of claim 68 wherein the source of bias current further comprises a voltage source, Vb, and a current limiting resistor.
70. The apparatus of claim 67 wherein the sense circuit provides an indication of when the magnetizing current crosses zero.
71. The apparatus of claim 67 wherein the sense circuit produces a signal which inhibits ( enables ) initiation of another converter operating cycle before ( after ) the magnetizing current crosses zero.
72. The apparatus of claim 67 wherein the sense circuit produces a signal which inhibits ( enables ) initiation of another converter operating cycle before ( after ) the magnetizing current has passed through a predefined value.
73. The apparatus of claim 62 , 66 , 67 , 70 , 71 , or 72 wherein the sense circuit provides a signal indicating that the primary switch has entered an OFF state.
74. The apparatus of claim 73 wherein the reset circuitry further comprises a switch controller, the switch controller causing the switch circuitry to enter the closed state after the primary switch has entered the OFF state.
75. The apparatus of claim 74 wherein:
the primary switch further comprises a primary - switch diode connected in parallel across the primary switch and poled to block current flow from the DC input source to the primary winding of the transformer; and
further comprising
a primary switch sense circuit connected to sense current flowing in the primary - switch diode;
wherein the primary switch sense circuit initiates turning on the primary switch after a current flows through the primary - switch diode indicating that capacitances associated with the primary switch have discharged.
76. The apparatus of claim 35 further comprising,
a sense circuit connected to the series circuit for detecting completion of the forward energy transfer portion of the converter operating cycles.
77. The apparatus of claim 76 wherein the sense circuit senses magnetizing current flowing between the transformer and the reset capacitor.
78. The apparatus of claim 77 wherein:
the series circuit further comprises a first unidirectional conducting device poled to conduct a magnetizing current during a first portion of a magnetizing energy recycling portion of each of the succession of the converter operating cycles; and
the sense circuit senses the current flowing in the first unidirectional conducting device.
79. The apparatus of claim 78 wherein:
the series circuit further comprises an impedance connected in series with the first unidirectional conducting device and the sense circuit senses a voltage across the impedance induced by the magnetizing current.
80. The apparatus of claim 79 wherein the impedance comprises a resistor.
81. The apparatus of claim 79 wherein the first unidirectional conducting device comprises a diode.
82. The apparatus of claim 78 wherein the sense circuit senses a voltage across the first unidirectional conducting device.
83. The apparatus of claim 82 wherein the sense circuit further comprises:
a source of bias current connected through a second unidirectional conducting device to the capacitor leg side of the first unidirectional conducting device, the bias current and second unidirectional conducting device being poled to reverse bias the first unidirectional conducting device; and
the sense circuit senses the voltage, Vs, across the series combination of the first and second unidirectional conducting devices.
84. The apparatus of claim 83 wherein the second unidirectional conducting device comprises a diode.
85. The apparatus of claim 84 wherein the source of bias current further comprises a voltage source, Vb, and a current limiting resistor.
86. The apparatus of claim 83 wherein the sense circuit provides an indication of when the magnetizing current crosses zero.
87. The apparatus of claim 83 wherein the sense circuit produces a signal which inhibits ( enables ) initiation of another converter operating cycle before ( after ) the magnetizing current crosses zero.
88. The apparatus of claim 83 wherein the sense circuit produces a signal which inhibits ( enables ) initiation of another converter operating cycle before ( after ) the magnetizing current has passed through a predefined value.
89. The apparatus of claim 78 , 82 , 83 , 86 , 87 , or 88 wherein the sense circuit provides a signal indicating that the primary switch has entered an OFF state.
90. The apparatus of claim 89 wherein the reset circuitry further comprises a switch controller, the switch controller causing the switch circuitry to enter the closed state after the primary switch has entered the OFF state.
91. The apparatus of claim 90 wherein:
the primary switch further comprises a primary - switch diode connected in parallel across the primary switch and poled to block current flow from the DC input source to the primary winding of the transformer; and
further comprising
a primary switch sense circuit connected to sense current flowing in the primary - switch diode;
wherein the primary switch sense circuit initiates turning on the primary switch after a current flows through the primary - switch diode indicating that capacitances associated with the primary switch have discharged.
92. The apparatus of claim 39 further comprising,
a sense circuit connected to the series circuit for detecting completion of a forward energy transfer portion of the converter operating cycles.
93. The apparatus of claim 92 wherein the sense circuit senses magnetizing current flowing between the transformer and the reset capacitor.
94. The apparatus of claim 93 wherein:
the series circuit further comprises a first unidirectional conducting device poled to conduct a magnetizing current during a first portion of a magnetizing energy recycling portion of each of the succession of the converter operating cycles; and
the sense circuit senses the current flowing in the first unidirectional conducting device.
95. The apparatus of claim 94 wherein:
the series circuit further comprises an impedance connected in series with the first unidirectional conducting device and the sense circuit senses a voltage across the impedance induced by the magnetizing current.
96. The apparatus of claim 95 wherein the impedance comprises a resistor.
97. The apparatus of claim 95 wherein the first unidirectional conducting device comprises a diode.
98. The apparatus of claim 94 wherein the sense circuit senses a voltage across the first unidirectional conducting device.
99. The apparatus of claim 98 wherein the sense circuit further comprises:
a source of bias current connected through a second unidirectional conducting device to the capacitor leg side of the first unidirectional conducting device, the bias current and second unidirectional conducting device being poled to reverse bias the first unidirectional conducting device; and
the sense circuit senses the voltage, Vs, across the series combination of the first and second unidirectional conducting devices.
100. The apparatus of claim 99 wherein the second unidirectional conducting device comprises a diode.
101. The apparatus of claim 100 wherein the source of bias current further comprises a voltage source, Vb, and a current limiting resistor.
102. The apparatus of claim 99 wherein the sense circuit provides an indication of when the magnetizing current crosses zero.
103. The apparatus of claim 99 wherein the sense circuit produces a signal which inhibits ( enables ) initiation of another converter operating cycle before ( after ) the magnetizing current crosses zero.
104. The apparatus of claim 99 wherein the sense circuit produces a signal which inhibits ( enables ) initiation of another converter operating cycle before ( after ) the magnetizing current has passed through a predefined value.
105. The apparatus of claim 94 , 98 , 99 , 102 , 103 , or 104 wherein the sense circuit provides a signal indicating that the primary switch has entered an OFF state.
106. The apparatus of claim 105 wherein the reset circuitry further comprises a switch controller, the switch controller causing the switch circuitry to enter the closed state after the primary switch has entered the OFF state.
107. The apparatus of claim 106 wherein:
the primary switch further comprises a primary - switch diode connected in parallel across the primary switch and poled to block current flow from the DC input source to the primary winding of the transformer; and
further comprising
a primary switch sense circuit connected to sense current flowing in the primary - switch diode;
wherein the primary switch sense circuit initiates turning on the primary switch after a current flows through the primary - switch diode indicating that capacitances associated with the primary switch have discharged.
108. The method of claim 40 further comprising:
sensing completion of the forward energy transfer portion of the converter operating cycles.
109. The method of claim 108 wherein the sensing further comprises sensing magnetizing current flowing between a winding of the transformer and the reset capacitor.
110. The method of claim 109 wherein the sensing further comprises allowing the magnetizing current to flow through an impedance connected between the winding of the transformer and the reset capacitor and sensing a voltage induced in the impedance by the magnetizing current.
111. The method of claim 110 wherein the impedance is a resistor.
112. The method of claim 110 further comprising allowing the magnetizing current to flow through a first unidirectional conducting device in series with the impedance.
113. The method of claim 109 further comprising allowing the magnetizing current to flow through a first unidirectional conducting device connected between the winding of the transformer and the reset capacitor and sensing a voltage across the first unidirectional conducting device.
114. The method of claim 113 wherein the sensing further comprises:
providing a source of bias current connected through a second unidirectional conducting device to the reset capacitor side of the first unidirectional conducting device, the bias current and second unidirectional conducting device being poled to reverse bias the first unidirectional conducting device; and
sensing the voltage, Vs, across the series combination of the first and second unidirectional conducting devices.
115. The method of claim 114 wherein the second unidirectional conducting device comprises a diode.
116. The method of claim 115 wherein the source of bias current further comprises a voltage source, Vb, and a current limiting resistor.
117. The method of claim 114 wherein the sensing further comprises detecting a value of Vs corresponding to when the magnetizing current crosses zero.
118. The method of claim 117 further comprising inhibiting initiation of another converter operating cycle until Vs indicates that the magnetizing current crosses zero.
119. The method of claim 117 further comprising inhibiting initiation of another converter operating cycle until Vs indicates that the magnetizing current has passed through a predefined value.
120. The method of claim 109 , 113 , or 114 further comprising closing a reset switch after completion of the forward energy transfer portion of the converter operating cycles.
121. The method of claim 120 wherein:
said connecting comprises using a primary switch and further comprising
providing a primary - switch diode connected in parallel across the primary switch and poled to block current flow from a DC input source to the winding of the transformer; and
sensing current flowing in the primary - switch diode;
turning on the primary switch after a current flows through the primary - switch diode indicating that capacitances associated with the primary switch have discharged.
122. Apparatus for use in a switching power converter of the kind having
a transformer,
a primary switch for connecting a DC input source to a winding of the transformer during a portion of each of a series of converter operating cycles, and
a reset capacitor, the apparatus comprising:
a first unidirectional conducting device connected between a winding of the transformer and the reset capacitor to conduct a magnetizing current during a first portion of a magnetizing energy recycling portion of the converter operating cycles, the first unidirectional conducting device being poled to conduct the magnetizing current which flows at the time that the primary switch is opened; and
a sense circuit connected to sense the current flowing in the unidirectional conducting device.
123. The apparatus of claim 122 further comprising a resistance in series with the first unidirectional conducting device; and wherein the sense circuit senses the voltage across the resistance.
124. The apparatus of claim 122 wherein:
the first unidirectional conducting device comprises a diode; and
the sense circuit senses the voltage across the diode.
125. The apparatus of claim 124 further comprising:
a source of bias current, connected through a second unidirectional conducting device to the reset capacitor side of the first unidirectional conducting device;
the bias current and second unidirectional conducting device being poled to reverse bias the first unidirectional conducting device; and
wherein the sense circuit senses the voltage, Vs, across the series combination of the first and second unidirectional conducting devices.
126. The apparatus of claim 125 wherein the second unidirectional conducting device comprises a diode.
127. The apparatus of claim 126 wherein the source of bias current further comprises a voltage source, Vb, and a current limiting resistor.
128. The apparatus of claim 125 wherein the sense circuit provides an indication of when the magnetizing current crosses zero.
129. The apparatus of claim 125 wherein the sense circuit produces a signal for inhibiting ( enabling ) initiation of another converter operating cycle before ( after ) the magnetizing current crosses zero.
130. The apparatus of claim 125 wherein the sense circuit produces a signal for inhibiting ( enabling ) initiation of another converter operating cycle before ( after ) the magnetizing current has passed through a predefined value.
131. The apparatus of claim 122 , 124 , 125 , 128 , 129 or 130 wherein the sense circuit provides a signal indicating that the primary switch has entered an OFF state.
132. The apparatus of claim 131 further comprises a switch controller configured to cause a reset switch to enter a closed state after the primary switch has entered the OFF state.
133. The apparatus of claim 132 further comprising:
a primary - switch diode connected in parallel across the primary switch and poled to block current flow from the DC input source to the primary winding of the transformer; and
a primary switch sense circuit connected to sense current flowing in the primary - switch diode;
wherein the primary switch sense circuit is configured to initiate turning on the primary switch after a current flows through the primary - switch diode indicating that capacitances associated with the primary switch have discharged.
134. A method for use in a switching power converter of the kind having
a transformer,
a primary switch for connecting a DC input source to a winding of the transformer during a portion of each of a series of converter operating cycles, and
a reset capacitor, the method comprising:
providing a first unidirectional conducting device between a winding of the transformer and the reset capacitor to conduct a magnetizing current during a first portion of a magnetizing energy recycling portion of the converter operating cycles, the first unidirectional conducting device being poled to conduct the magnetizing current which flows at the time that the primary switch is opened; and
sensing current flowing in the unidirectional conducting device.
135. The method of claim 134 further comprising:
providing a resistance in series with the first unidirectional conducting device; and
the sensing comprises sensing the voltage across the resistance.
136. The method of claim 134 wherein:
the first unidirectional conducting device comprises a diode; and
the sensing comprises sensing the voltage across the diode.
137. The method of claim 136 further comprising:
providing a source of bias current, connected through a second unidirectional conducting device to the reset capacitor side of the first unidirectional conducting device;
the bias current and second unidirectional conducting device being poled to reverse bias the first unidirectional conducting device; and
the sensing comprises sensing the voltage, Vs, across the series combination of the first and second unidirectional conducting devices.
138. The method of claim 137 wherein the second unidirectional conducting device comprises a diode.
139. The method of claim 138 wherein the source of bias current further comprises a voltage source, Vb, and a current limiting resistor.
140. The method of claim 137 wherein the sensing further comprises detecting a value of Vs corresponding to when the magnetizing current crosses zero.
141. The method of claim 140 further comprising inhibiting initiation of another converter operating cycle until Vs indicates that the magnetizing current crosses zero.
142. The method of claim 140 further comprising inhibiting initiation of another converter operating cycle until Vs indicates that the magnetizing current has passed through a predefined value.
143. The method of claim 134 , 136 , or 137 further comprising closing a reset switch after completion of the forward energy transfer portion of the converter operating cycles.
144. The method of claim 143 further comprising:
providing a primary - switch diode connected in parallel across the primary switch and poled to block current flow from a DC input source to the winding of the transformer; and
sensing current flowing in the primary - switch diode;
turning on the primary switch after a current flows through the primary - switch diode indicating that capacitances associated with the primary switch have discharged.Cited by (0)
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