Driving semiconductor switches in power converters
An electronic switch driver improves control of semiconductor switches in resonant power trains, improves ZVS operation, eases design challenges, improves manufacturability, and scalability of power converter design. Individual switch timing control is offloaded from the main power train controller, eliminating the effects of parasitic impedances and timing errors, particularly in high power, large power trains. Deployed locally at each controlled switch, the driver circuit includes logic to optimize ZVS operation of the controlled switch in steady state operation and ensures continuity of operation, e.g. during start-up and other conditions under which ZVS may not be achieved. The driver circuit may turn the controlled switch OFF quickly in response to an ON command, ON quickly in response to an ON command when predetermined conditions, e.g. ZVS, exist; and ON slowly in response to an ON command when predetermined conditions, e.g. ZVS, do not exist.
1 . An apparatus for operating a semiconductor switch having a gate terminal, a source terminal, and a drain terminal, the apparatus comprising:
driver circuitry having a first input for receiving a switch control signal, an output for connection to the gate terminal, a common terminal for connection to the source terminal, and a second input for sensing the drain terminal, the driver circuitry including:
a first switch to turn off the gate terminal in response to an OFF signal at the first input;
a threshold detector connected to the second input and constructed and arranged to provide a ZVS signal indicating whether the drain-to-source voltage level is below a predetermined threshold;
a second switch to turn on the gate terminal after an ON signal is received at the first input and the ZVS signal is received from the threshold detector;
a slope detector connected to the second input and constructed and arranged to provide a slope signal indicating the rate of change of the drain-to-source voltage level;
gate slew control circuitry constructed and arranged to control a rate of change of voltage at the output for slowly turning ON the semiconductor switch in response to an ON signal at the first input and the slope signal if the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold.
2 . The apparatus of claim 1 wherein the driver circuitry is constructed and arranged to:
(a) turn the semiconductor switch OFF quickly using the first switch in response to an OFF signal at the first input;
(b) turn the semiconductor switch ON slowly using the gate slew control circuitry in response to a ON signal at the first input and the slope signal while the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold; and
(c) turn the semiconductor switch ON quickly using the second switch in response to a ON signal at the first input once the ZVS signal indicates the drain-to-source voltage is below the predetermined threshold.
3 . The apparatus of claim 2 wherein the driver circuitry is configured to (a) turn the semiconductor switch OFF within a first time duration using the first switch in response to the OFF signal at the first input, (b) turn the semiconductor switch ON slowly within a second time duration using the gate slew control circuitry in response to the ON signal at the first input and the slope signal while the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold, and (c) turn the semiconductor switch ON within a third time duration using the second switch in response to the ON signal at the first input once the ZVS signal indicates the drain-to-source voltage is below the predetermined threshold;
wherein the first time duration is less than 33% of the second time duration, and the third time duration is less than 33% of the second time duration.
4 . The apparatus of claim 2 wherein the driver circuitry is further constructed and arranged to:
(d) adjust the rate of change of voltage at the output as a function of the slope signal while the ON signal is present at the first input and the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold.
5 . The apparatus of claim 4 wherein the driver circuitry is configured to decrease the rate of change of voltage at the output in response to an increase of the slope signal while the ON signal is present at the first input and the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold.
6 . The apparatus of claim 1 wherein the driver circuitry is constructed and arranged to:
(a) turn the semiconductor switch OFF quickly using the first switch in response to an OFF signal at the first input;
(b) slowly increase a voltage at the output in response to an ON signal at the first input while the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold;
(c) turn the semiconductor switch ON with a predetermined minimum delay in response to an ON signal at the first input using the second switch if the ZVS signal indicates the drain-to-source voltage is below the predetermined threshold; wherein the driver circuitry establishes a maximum delay for turning the semiconductor switch ON after an ON signal is received at the first input and a minimum delay for turning the semiconductor switch ON after the ZVS signal indicates the drain-to-source voltage is below the predetermined threshold.
7 . The apparatus of claim 6 wherein the driver circuitry is configured to
(a) turn the semiconductor switch OFF within a first time duration using the first switch in response to the OFF signal at the first input;
(b) increase the voltage at the output from a first level that causes the semiconductor switch to be OFF to a second level that causes the semiconductor switch to be ON within a second time duration in response to the ON signal at the first input while the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold;
(c) turn the semiconductor switch ON within a third time duration in response to the ON signal at the first input using the second switch if the ZVS signal indicates the drain-to-source voltage is below the predetermined threshold;
wherein the first time duration is less than 33% of the second time duration, and the third time duration is less than 33% of the second time duration.
8 . The apparatus of claim 6 wherein the driver circuitry is configured to turn the semiconductor switch ON with a delay that ranges from a predetermined minimum value to a predetermined maximum value,
wherein the driver circuitry is configured to turn the semiconductor switch ON with a delay having the maximum delay value after the ON signal is received at the first input while the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold;
wherein the driver circuitry is configured to turn the semiconductor switch ON with a delay having the predetermined minimum value in response to the ON signal at the first input using the second switch if the ZVS signal indicates the drain-to-source voltage is below the predetermined threshold.
9 . The apparatus of claim 6 wherein the driver circuitry is further constructed and arranged to adjust a delay for turning the semiconductor switch ON after the ON signal is received at the first input as a function of the slope signal.
10 . The apparatus of claim 9 wherein the driver circuitry is further constructed and arranged to increase the time required to turn the semiconductor switch ON slowly after the ON signal is received at the first input for a slope signal indicating an increased rate of change of the drain-to-source voltage level.
11 . The apparatus of claim 9 wherein the driver circuitry is further constructed and arranged to decrease the time required to turn the semiconductor switch ON slowly after the ON signal is received at the first input for a slope signal indicating a decreased rate of change of the drain-to-source voltage level.
12 . The apparatus of claim 9 wherein the driver circuitry is configured to set a larger delay for turning the semiconductor switch ON after the ON signal is received at the first input and the slope signal has larger value, and set a smaller delay for turning the semiconductor switch ON after the ON signal is received at the first input and the slope signal has smaller value.
13 . The apparatus of claim 1 wherein the predetermined threshold is equal to a transition voltage for an output capacitance of the respective switch, such that the output capacitance, Coss, of the respective switch increases exponentially as a function of reductions in the drain-to-source voltage of the respective switch below the predetermined threshold.
14 . The apparatus of claim 1 wherein the predetermined threshold is greater than a transition voltage for an output capacitance of the respective switch, such that the output capacitance, Coss, of the respective switch increases exponentially as a function of reductions in the drain-to-source voltage of the respective switch below the predetermined threshold.
15 . The apparatus of claim 1 wherein the first switch and the second switch have one or more components in common.
16 . The apparatus of claim 15 wherein the first switch comprises a current sink that is activated in response to the OFF signal.
17 . The apparatus of claim 16 wherein the second switch comprises a first current source that is activated in response to the ON signal received at the first input and the ZVS signal received from the threshold detector.
18 . The apparatus of claim 17 wherein the gate slew control circuitry comprises a second current source configured to provide a current that is adjusted based on the slope signal if the ZVS signal indicates the drain-to-source voltage is above the predetermined threshold.
19 . Apparatus for converting power from an input for delivery to an output, the apparatus comprising:
a power train including one or more input switches constructed and arranged to selectively connect a resonant circuit including a transformer to the input, and one or more output switches constructed and arranged to selectively connect the transformer to the output;
a switch timing controller constructed and arranged to generate timing signals to operate the power train in a series of converter operating cycles;
one or more switch drivers having an input connected to receive selected ones of the timing signals from the switch timing controller;
wherein at least some of the input switches or the output switches, or both include a switch control terminal, a common terminal, and a switched terminal that is controlled by a respective switch driver;
each switch driver including a first input for receiving a switch control signal from the switch controller, an output for connection to the control terminal of its respective switch, a reference terminal for connection to the common terminal of its respective switch, a second input for sensing circuit conditions at the switched terminal of its respective switch, and a power input for receiving power to operate, the switch driver including:
a first current sink connected to sink a first current from the output in response to an OFF signal at the first input;
a threshold detector connected to the second input and constructed and arranged to provide a ZVS signal indicating that a voltage, Vsw, across the switched terminal and the common terminal of its respective switch is at or below a predetermined threshold;
a first current source connected to deliver a first current to the output in response to an ON signal at the first input if the ZVS signal is received from the threshold detector;
a slope detector connected to the second input and constructed and arranged to provide a slope signal indicating the rate of change of the voltage, Vsw, across the switched terminal and the common terminal of its respective switch;
a second current source connected to deliver a second current to the output in response to an ON signal at the first input, the second current being adjusted by the slope signal.
20 . The apparatus of claim 19 wherein each switch driver is constructed and arranged to:
(a) turn its respective switch OFF quickly using the first current sink in response to an ON signal at the first input;
(b) turn its respective switch ON slowly using the second current source in response to an ON signal at the first input;
(c) turn its respective switch ON quickly using the first current source in response to an ON signal at the first input when the voltage Vsw of its respective switch is below the predetermined threshold; and
(e) adjust the rate at which the respective switch is turned ON based upon the rate of change of the voltage Vsw of its respective switch.
21 . The apparatus of claim 20 wherein one or more of the at least some switches include a plurality of semiconductor switches connected in parallel to function as a single switch, and a plurality of respective switch drivers connected to operate respective ones of the plurality of semiconductor switches.
22 . The apparatus of claim 20 wherein each switch driver is constructed and arranged to adjust a delay for turning the respective switch ON after the ON signal is received at the first input as a function of the slope signal;
wherein the switch driver is constructed and arranged to increase the time required to turn the respective switch ON slowly after the ON signal is received at the first input for a slope signal indicating an increased rate of change of the switched terminal voltage level;
wherein the switch driver is constructed and arranged to decrease the time required to turn the respective switch ON slowly after the ON signal is received at the first input for a slope signal indicating a decreased rate of change of the switched terminal voltage level.
23 . The apparatus of claim 19 wherein the one or more switch drivers comprise a plurality of switch drivers, the apparatus further comprising:
a gate drive transformer having a primary winding connected to receive timing signals from the switch timing controller and a plurality of secondary windings each connected to an input of a respective one of the plurality of switch drivers.
24 . The apparatus of claim 23 wherein one or more of the at least some switches include a plurality of semiconductor switches connected in parallel to function as a single switch, and a plurality of respective switch drivers connected to operate respective ones of the plurality of semiconductor switches.
25 . Apparatus for converting power from an input for delivery to output terminals, the apparatus comprising:
a switching power conversion stage having a power train including a plurality of distributed output switches constructed and arranged to selectively conduct power from the power train to the output terminals;
each output switch including a switch control terminal, a common terminal, and a switched terminal;
each output switch being driven by a respective switch driver physically located proximal to said switch;
a switch timing controller constructed and arranged to generate timing signals to operate the power train including the plurality of distributed output switches, in a series of converter operating cycles;
a gate drive transformer having a primary winding connected to receive ON and OFF signals from the switch timing controller and a plurality of secondary windings each connected to deliver ON and OFF signals to one or more respective switch drivers;
wherein each switch driver includes a first input connected to a respective secondary winding of the gate drive transformer to receive the ON and OFF signals from the timing controller, an output for connection to the control terminal of its respective switch, a reference terminal for connection to the common terminal of its respective switch, a second input for sensing circuit conditions at the switched terminal of its respective switch, and a power input connected to the respective secondary winding of the gate drive transformer for receiving power to operate,
the switch driver including circuitry operative to: quickly turn OFF the respective switch in response to the OFF signal at the first input, turn ON the respective switch in response to an ON signal at the first input if the voltage (Vsw) across the switched and common terminals of the respective switch is below a predetermined threshold; and control a rate of change of voltage at the output for slowly turning ON the respective power switch in response to an ON signal at the first input if the voltage (Vsw) across the switched and common terminals of the respective switch is above the predetermined threshold.
26 . The apparatus of claim 25 wherein each of at least some of the switch drivers comprises:
a threshold detector connected to the second input and constructed and arranged to provide a zero-voltage switching (ZVS) signal indicating whether the voltage Vsw across the switched and common terminals of the respective switch is below the predetermined threshold;
a slope detector connected to the second input and constructed and arranged to provide a slope signal indicating the rate of change of the voltage Vsw across the switched and common terminals of the respective switch; and
gate slew control circuitry constructed and arranged to control the rate of change of voltage at the output for slowly turning ON the respective switch in response to an ON signal at the first input and the slope signal if the ZVS signal indicates the voltage Vsw across the switched and common terminals of the respective switch is above the predetermined threshold.
27 . The apparatus of claim 26 wherein each of at least some of the switch drivers is constructed and arranged to adjust a delay for turning the respective switch ON after the ON signal is received at the first input as a function of the slope signal;
wherein each switch driver is further constructed and arranged to increase the time required to turn the respective switch ON slowly after the ON signal is received at the first input for a slope signal indicating an increased rate of change of the voltage Vsw across the switched and common terminals of the respective switch.
28 . The apparatus of claim 27 wherein each of at least some of the switch drivers is further constructed and arranged to decrease the time required to turn the respective switch ON slowly after the ON signal is received at the first input for a slope signal indicating a decreased rate of change of the voltage Vsw across the switched and common terminals of the respective switch.
29 . The apparatus of claim 26 wherein each of at least some of the switch drivers comprises:
a first current source connected to deliver a first current to the output in response to an ON signal at the first input if the ZVS signal indicates that the voltage Vsw across the switched and common terminals of the respective switch is below the predetermined threshold; and
a second current source connected to deliver a second current to the output in response to an ON signal at the first input, the second current being adjusted by the slope signal.
30 . The apparatus of claim 25 wherein the driver circuit includes circuitry configured to turn OFF the respective switch within a first time duration in response to the OFF signal at the first input, turn ON the respective switch within a second time duration in response to the ON signal at the first input if the voltage Vsw across the switched and common terminals of the respective switch is below the predetermined threshold, and control the rate of change of voltage at the output for turning ON the respective power switch within a third time duration in response to the ON signal at the first input if the voltage Vsw across the switched and common terminals of the respective switch is above the predetermined threshold;
wherein the first time duration is less than 33% of the third time duration, and the second time duration is less than 33% of the third time duration.
31 . The apparatus of claim 25 wherein each switch driver includes:
a first current sink connected to sink a first current from the output in response to an OFF signal at the first input;
a threshold detector connected to the second input and constructed and arranged to provide a zero-voltage switching (ZVS) signal indicating that a voltage, Vsw, across the switched terminal and the common terminal of its respective output switch is at or below a predetermined threshold;
a first current source connected to deliver a first current to the output in response to an ON signal at the first input if the ZVS signal is received from the threshold detector;
a slope detector connected to the second input and constructed and arranged to provide a slope signal indicating the rate of change of the voltage, Vsw, across the switched terminal and the common terminal of its respective output switch;
a second current source connected to deliver a second current to the output in response to an ON signal at the first input, the second current being adjusted by the slope signal.
32 . The apparatus of claim 25 wherein each switch driver is constructed and arranged to adjust a delay for turning the respective output switch ON after the ON signal is received at the first input as a function of the slope signal;
wherein the switch driver is constructed and arranged to increase the time required to turn the respective output switch ON slowly after the ON signal is received at the first input for a slope signal indicating an increased rate of change of the switched terminal voltage level;
wherein the switch driver is constructed and arranged to decrease the time required to turn the respective switch ON slowly after the ON signal is received at the first input for a slope signal indicating a decreased rate of change of the switched terminal voltage level.
33 . A method of operating a power converter comprising:
providing a plurality of power switches to operate a power train, each power switch having a respective gate, source, and drain terminals, and a drain-source voltage, Vsw;
providing a switch timing controller constructed and arranged to provide ON and OFF switch control signals to operate the power train;
providing a switch driver for operating a respective power switch;
providing each switch driver a first input for receiving the switch control signals, an output for connection to the gate terminal, a common terminal for connection to the source terminal, and a second input for sensing the drain terminal, of the respective power switch;
using the switch driver to quickly turn off the respective power switch in response to the OFF signal at the first input, turn on the respective power switch in response to an ON signal at the first input if the drain-source voltage, Vsw, of the respective power switch is below a predetermined threshold, and control a rate of change of voltage at the output for slowly turning ON the respective power switch in response to an ON signal at the first input if the drain-source voltage, Vsw, of the respective power switch is above the predetermined threshold.
34 . The method of claim 33 , comprising:
providing a plurality of switch drivers;
providing a gate drive transformer having a primary winding constructed and arranged to receive the switch control signals from the switch timing controller and a plurality of secondary windings; and
connecting each secondary winding to the first input of a respective switch driver.
35 . The method of claim 34 , comprising:
providing a plurality of semiconductor switches having the source and drain terminals connected in parallel for predetermined ones of the plurality of power switches; and
providing a switch driver for each semiconductor switch in the plurality of semiconductor switches;
wherein the drain-source voltage, Vsw, of each predetermined one power switch is substantially equal to the drain-source voltage, Vds, of each respective semiconductor switch.
36 . The method of claim 35 further comprising:
providing a second plurality of semiconductor switches for predetermined others of the plurality of power switches;
connecting the semiconductor switches of the second plurality in series to divide the drain-source voltage, Vsw, of each predetermined other power switch, wherein the drain-source voltage, Vds, of each semiconductor switch of the second plurality is a fraction of the drain-source voltage, Vsw, of the predetermined other power switch;
providing a respective switch driver for each semiconductor switch of the second plurality; and
connecting the first input of each respective switch driver to a respective secondary winding to receive the switch control signals via the gate drive transformer.
37 . The method of claim 36 further comprising:
providing an auxiliary input for each respective switch driver;
connecting the auxiliary input of each respective switch driver to the respective secondary winding;
using each respective switch driver to harness energy in the switch control signals received from the respective secondary winding; and
using the energy to operate the respective switch.
38 . The method of claim 34 , further comprising providing a resonant circuit including a transformer for the power train and wherein the switch timing controller is constructed and arranged to operate the power train such that an output voltage of the power train divided by an input voltage to the power train is a fixed-ratio subject to an output resistance.
39 . The method of claim 38 , further comprising using a current flowing in the transformer to reduce the drain-source voltage of the respective switch prior to turning the respective switch ON.
40 . The method of claim 39 , further comprising providing a plurality of semiconductor switches having the source and drain terminals connected in parallel for predetermined ones of the plurality of power switches and providing a switch driver for each semiconductor switch in the plurality of semiconductor switches.
41 . The method of claim 39 , further comprising:
providing a plurality of semiconductor switches for predetermined ones of the plurality of power switches;
connecting the semiconductor switches in series to divide the drain-source voltage, Vsw, of each predetermined one power switch, wherein the drain-source voltage, Vds, of each semiconductor switch is a fraction of the drain-source voltage, Vsw, of the predetermined one power switch;
providing a respective switch driver for each semiconductor switch; and
connecting the first input of each respective switch driver to a respective secondary winding to receive the switch control signals via the gate drive transformer.
42 . The method of claim 41 further comprising:
providing an auxiliary input for each respective switch driver;
connecting the auxiliary input of each respective switch driver to the respective secondary winding;
using the switch driver to harness energy in the switch control signals received from the respective secondary winding; and
using the energy to operate the respective switch.
43 . The method of claim 33 , further comprising using a current flowing in an inductive component to reduce the drain-source voltage of the respective switch prior to turning the respective switch ON.
44 . The method of claim 33 , further comprising providing an inductive component for the power train and wherein the switch timing controller is constructed and arranged to operate the power train to control an output variable of the power train.
45 . The method of claim 44 wherein the switch timing controller is constructed and arranged to operate the power train to convert power either in a forward direction from an input to an output or in a reverse direction from an output to an input.
46 . The method of claim 45 , further comprising providing a plurality of semiconductor switches having the source and drain terminals connected in parallel for predetermined ones of the plurality of power switches and providing a switch driver for each semiconductor switch in the plurality of semiconductor switches.
47 . The method of claim 44 , further comprising using a current flowing in the inductive component to reduce the drain-source voltage, Vsw, of the respective power switch prior to turning the respective switch ON.
48 . The method of claim 47 , further comprising providing a plurality of semiconductor switches having the source and drain terminals connected in parallel for predetermined ones of the plurality of power switches and providing a switch driver for each semiconductor switch in the plurality of semiconductor switches.
49 . The method of claim 44 wherein the switch timing controller is constructed and arranged to operate the power train to control an output voltage.
50 . The method of claim 44 wherein the switch timing controller is constructed and arranged to operate the power train to control an output current.
51 . The method of claim 44 , further comprising:
providing a gate drive transformer having a primary winding connected to receive the switch control signals from the switch timing controller and a plurality of secondary windings;
providing a plurality of semiconductor switches for predetermined ones of the plurality of power switches;
connecting the semiconductor switches in series to divide the drain-source voltage, Vsw, of each predetermined one power switch, wherein the drain-source voltage, Vds, of each semiconductor switch is a fraction of the drain-source voltage, Vsw, of the predetermined one power switch;
providing a respective switch driver for each semiconductor switch; and
connecting the first input of each respective switch driver to a respective secondary winding to receive the switch control signals via the gate drive transformer.
52 . The method of claim 51 , further comprising:
providing an auxiliary input for each respective switch driver;
connecting the auxiliary input of each respective switch driver to the respective secondary winding;
using the switch driver to harness energy in the switch control signals received from the respective secondary winding; and
using the energy to operate the respective switch.
53 . The method of claim 33 , further comprising:
setting the predetermined threshold to a voltage that approximates a transition voltage for an output capacitance of the respective switch, such that the output capacitance, Coss, of the respective switch increases exponentially as the drain-to-source voltage decreases below the predetermined threshold.
54 . The method of claim 33 , wherein turning on or off the respective power switch comprises using the switch driver to turn off the respective power switch within a first time duration in response to the OFF signal at the first input, turn on the respective power switch within a second time duration in response to the ON signal at the first input if the drain-source voltage Vsw of the respective power switch is below the predetermined threshold, and control the rate of change of voltage at the output for turning on the respective power switch within a third time duration in response to the ON signal at the first input if the drain-source voltage Vsw of the respective switch is above the predetermined threshold;
wherein the first time duration is less than 33% of the third time duration, and the second time duration is less than 33% of the third time duration.
55 . A method of operating a power converter comprising:
providing a plurality of power switches to operate a power train, including an inductive component, each power switch having a respective gate, source, and drain terminal, a drain-to-source output capacitance, a drain-source voltage, Vsw, and a transition voltage, Vtr, for the output capacitance, Coss, wherein Coss=c 1 when Vsw=Vtr, Coss=c 2 when Vsw=40V, and c 1 =2×c 2 ;
providing a switch timing controller constructed and arranged to provide ON and OFF switch control signals to operate the power train;
providing a switch driver for operating a respective power switch;
the switch driver having a first input for receiving the switch control signals, an output for connection to the gate terminal, a common terminal for connection to the source terminal, and a second input for sensing the drain terminal, of the respective power switch;
using the switch driver to quickly turn off the respective switch in response to the OFF signal at the first input, turn on the respective switch in response to an ON signal at the first input if the drain-source voltage, Vsw, of the respective switch is below a predetermined threshold, and control a rate of change of voltage at the output for slowly turning ON the respective power switch in response to an ON signal at the first input if the drain-source voltage, Vsw, of the respective switch is above the predetermined threshold; and
setting the predetermined threshold to a voltage greater than the transition voltage for the output capacitance of the respective switch, such that the respective switch is turned ON to discharge its output capacitance, Coss, at a drain-source voltage, Vsw, that approximates the transition voltage.
56 . The method of claim 55 wherein providing the switch driver comprises:
providing a first current sink connected to sink a first current from the output in response to an OFF signal at the first input;
providing a threshold detector connected to the second input and constructed and arranged to provide a ZVS signal indicating that the voltage Vsw across the switched terminal and the common terminal of its respective output switch is at or below the predetermined threshold;
providing a first current source connected to deliver a first current to the output in response to an ON signal at the first input if the ZVS signal is received from the threshold detector;
providing a slope detector connected to the second input and constructed and arranged to provide a slope signal indicating the rate of change of the voltage, Vsw, across the switched terminal and the common terminal of its respective switch; and
providing a second current source connected to deliver a second current to the output in response to an ON signal at the first input, the second current being adjusted by the slope signal.
57 . The method of claim 56 wherein adjusting the second current by the slope signal comprises:
increasing the time required to turn the respective switch ON slowly after the ON signal is received at the first input for a slope signal indicating an increased rate of change of the switched terminal voltage level; and
decreasing the time required to turn the respective switch ON slowly after the ON signal is received at the first input for a slope signal indicating a decreased rate of change of the switched terminal voltage level.
58 . The method of claim 55 , comprising:
providing a gate drive transformer having a primary winding constructed and arranged to receive the switch control signals from the switch timing controller and a plurality of secondary windings; and
connecting each secondary winding to the first input of a respective switch driver.
59 . The method of claim 58 , further comprising:
providing a plurality of semiconductor switches having the source and drain terminals connected in parallel for predetermined ones of the plurality of power switches; and
providing a switch driver for each semiconductor switch in the plurality of semiconductor switches;
wherein the drain-source voltage, Vsw, of each predetermined one power switch is substantially equal to the drain-source voltage, Vds, of each respective semiconductor switch.
60 . The method of claim 55 , further comprising using a current flowing in an inductive component to reduce the drain-source voltage of the respective switch prior to turning the respective switch ON.
61 . The method of claim 60 , further comprising providing a resonant circuit including a transformer for the power train, and using the switch timing controller to operate the power train such that an output voltage of the power train divided by an input voltage to the power train is a fixed-ratio subject to an output resistance.
62 . The method of claim 61 , further comprising using a current flowing in the transformer to reduce the drain-source voltage of the respective switch prior to turning the respective switch ON.
63 . The method of claim 62 , further comprising providing a plurality of semiconductor switches having the source and drain terminals connected in parallel for predetermined ones of the plurality of power switches and providing a switch driver for each semiconductor switch in the plurality of semiconductor switches.
64 . The method of claim 55 , further comprising providing an inductive component for the power train and wherein the switch timing controller is constructed and arranged to operate the power train to control an output variable of the power train.
65 . The apparatus of claim 20 wherein each driver circuit is configured to:
(a) turn its respective switch OFF within a first time duration using the first current sink in response to the ON signal at the first input;
(b) turn its respective switch ON within a second time duration using the second current source in response to the ON signal at the first input; and
(c) turn its respective switch ON within a third time duration using the first current source in response to the ON signal at the first input when the voltage Vsw of its respective switch is below the predetermined threshold;
wherein the first time duration is less than 33% of the second time duration, and the third time duration is less than 33% of the second time duration.