U.S. patent application number 10/007882 was filed with the patent office on 2003-06-12 for half sine wave resonant drive circuit.
Invention is credited to Bennett, Paul George.
Application Number | 20030107413 10/007882 |
Document ID | / |
Family ID | 21728606 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030107413 |
Kind Code |
A1 |
Bennett, Paul George |
June 12, 2003 |
HALF SINE WAVE RESONANT DRIVE CIRCUIT
Abstract
A half sine wave resonant drive circuit provides a greater duty
cycle range of operation without a loss in power, particularly at
higher frequencies. A resonant circuit is capacitivly coupled to a
single switching device to provide the greater duty cycle range by
recycling the gate charge of the switching device through the
resonant circuit. A half sine wave drive signal is thereby produced
from an input square wave signal. The driving amplitude is constant
for operation over the range of duty cycles.
Inventors: |
Bennett, Paul George; (Stoke
Gifford, GB) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
21728606 |
Appl. No.: |
10/007882 |
Filed: |
December 6, 2001 |
Current U.S.
Class: |
327/108 |
Current CPC
Class: |
H03K 17/687 20130101;
H03K 17/04163 20130101; H03K 17/691 20130101; H03K 2217/0036
20130101 |
Class at
Publication: |
327/108 |
International
Class: |
H03B 001/00 |
Claims
What is claimed is:
1. A drive device providing improved operation and control of duty
cycle, the drive device comprising: switching means providing
operation at a duty cycle based upon a drive signal; and a gate
drive means for producing from an input signal a half sine wave
output signal for use as the drive signal to the switching means,
the gate drive means having a resonant circuit coupled to a gate of
the switching means.
2. The drive device according to claim 1 wherein the switching
means comprises a transistor and the gate drive means provides the
half sine wave output signal to the gate of the transistor.
3. The drive device according to claim 1 wherein the input signal
is a square wave and the resonant circuit is adapted to be
configured between an operating frequency and about twice the
operating frequency of the square wave input signal to thereby
provide a duty cycle of between about 50 percent and about 25
percent.
4. The drive device according to claim 3 wherein the resonant
circuit comprises a driver inductance and capacitance together
adapted to be configured to control the duty cycle based upon a
drive frequency defined by the square wave input signal.
5. The drive device according to claim 1 wherein the resonant
circuit comprises a driver inductance having a transformer and is
adapted to be configured to provide a duty cycle of between about
50 percent and about 75 percent.
6. The drive device according to claim 1 further comprising DC bias
means.
7. The drive device according to claim 1 wherein the resonant
circuit comprises a class E single ended resonant circuit
capacitivly coupled to the gate of the switching means.
8. The drive device according to claim 1 wherein the switching
means is a metal oxide semiconductor.
9. The drive device according to claim 3 further comprising a hard
switch for providing the square wave input signal.
10. A half sine wave drive circuit providing improved independent
amplitude and duty cycle control without power loss at higher
operating frequencies, the half sine wave drive circuit comprising:
a MOS controlled device to be switched to provide a duty cycle of
between about 25 percent and about 50 percent; and a resonant drive
circuit capacitivly coupled to a gate of the MOS controlled device
for providing from a periodic input signal a half sine wave output
signal for driving the MOS controlled device and adapted for
operation between an operating frequency and about twice the
operating frequency of the periodic input signal to thereby switch
the MOS controlled device.
11. The half sine wave drive circuit according to claim 10 wherein
the periodic input signal is a square wave and the resonant drive
circuit comprises a driver inductance and capacitance together
configurable to provide the duty cycle of between about 25 percent
and about 50 percent.
12. The half sine wave drive circuit according to claim 10 further
comprising a DC bias means.
13. The half sine wave drive circuit according to claim 10 wherein
the resonant drive circuit comprises a transformer providing a
driver inductance.
14. The half sine wave drive circuit according to claim 10 wherein
the MOS controlled device is a switching device comprising a
transistor.
15. The half sine wave drive circuit according to claim 10 adapted
for providing the duty cycle of between about 25 percent and about
50 percent during operation at frequencies exceeding 10 MHz.
16. The half sine wave drive circuit according to claim 11 further
comprising a hard switched input device for providing the square
wave input signal.
17. A method of controlling the duty cycle of a drive circuit
without losing power at higher operating frequencies, the method
comprising the steps of: receiving a periodic input signal;
producing a half sine wave output signal from the periodic input
signal using a resonant circuit capacitivly coupled to a switching
device; and configuring the resonant circuit to provide the half
sine wave output signal to thereby operate the switching device at
a duty cycle of between about 25 percent and about 50 percent.
18. The method according to claim 17 further comprising providing
DC bias to the resonant circuit.
19. The method according to claim 17 wherein the periodic input
signal is a square wave.
20. The method according to claim 17 further comprising using a
transformer in connection with the resonant circuit to add
isolation.
21. The method according to claim 17 further comprising using a
transformer in connection with the resonant circuit to invert the
driving waveform to provide a duty cycle of between about 50 and 75
percent.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to power electronic
devices, and more particularly to drive circuits for MOS gated
power electronic devices.
BACKGROUND OF THE INVENTION
[0002] Metal Oxide Semiconductor (MOS) devices are constructed
having a voltage controlled gate electrode. In operation, these
devices are turned on by the application of bias (i.e., voltage) to
the gate electrode. The gate provides capacitance to other
electrodes (e.g., source and drain electrodes in a
metal-oxide-silicon field-effect transistor) in these devices that
need to be charged and discharged in order to turn the device on
and off (i.e., charge is injected or extracted from the gate). In
determining the operating requirements of these devices, the charge
multiplied by the bias voltage represents a "turn on" and "turn
off" energy.
[0003] In many power semiconductor applications, the device must be
alternately turned on and off, often in conjunction with other
devices, to thereby form a power conversion circuit. There is a
desire to increase the frequency of operation (i.e., switching
speed) of such circuits, which allows these circuits to be
implemented with smaller and cheaper associated passive components.
However, with the frequency of operation increased, the power
required by the gate drive circuit increases proportionately (i.e.,
power equates to energy times frequency).
[0004] With respect specifically to gate drive circuits, half
bridge circuits are commonly used either discretely or as part of a
power MOS driver integrated circuit (IC). Using such a bridge type
circuit, the gate is charged and discharged from a voltage source
via the output resistance of the driver, the gate spreading
resistance of the controlled device and any added series
resistance. Thus, the forward and reverse passage of charge through
this resistance (i.e., the devices creating the resistance) results
in a power loss. It should be noted that this charge flows as the
driver switches, such that the driver will not necessarily be
saturated, thereby resulting in higher resistance than the quoted
"fully on" value of the driver. Reducing the resistance will not
help reduce the loss as it just enables the same charge to flow
more quickly.
[0005] In recent years, MOS gated power devices have replaced
bipolar devices in many applications as a result of the advantages
of MOS technology. For example, MOS gated power devices do not have
static (i.e., DC) drive power consumption. In these devices, some
AC power loss is acceptable, and at frequencies up to a few hundred
kilohertz (KHz), this loss is often insignificant compared to other
power losses in the circuit.
[0006] As frequencies are increased problems result. In particular,
switching losses may increase and power dissipation in the
switching device may also increase. In an attempt to address these
problems, zero voltage, zero current and resonant switching
techniques have been increasingly implemented in power conversion
circuits. These circuits typically recirculate or recycle the
energy involved in switching the device output capacitance, thereby
reducing the power dissipation of the device and increasing overall
efficiency.
[0007] Known devices, such as, for example, the MOS drive circuits
shown in FIGS. 1 and 2, use a high Q (i.e., quality factor, which
is a measure of the dissipation in a system) resonant circuit in
the gate circuit to "absorb" the gate capacitance, and generate a
sinusoidal gate voltage. Essentially, a filter circuit (i.e.,
single element high Q tuned circuit in FIG. 1 and a four element
filter circuit in FIG. 2) is provided to produce the sine wave
signal. Specifically, in a typical half bridge configuration, a
gate drive transformer is inserted between the resonant circuit and
gate, with the transformer phased such that each device is driven
with opposing phase. Correct switching of a driver device connected
to the resonant circuit can eliminate most of the driver loss.
However, only a very limited duty cycle is provided (i.e., at or
about 50 percent).
[0008] Full sine wave resonant drive circuits provide limited
control of duty cycle by varying amplitude, which affects the
crossing point of the waveform and the threshold voltage of the
driven device. In operation, reducing the drive voltage in order to
significantly reduce the duty cycle will result in low amplitude
past the gate threshold, and thus, poor saturation.
[0009] Therefore, known MOS drive circuits provide only very
limited effective duty cycle operation, which is essentially 50
percent less the delays between the zero crossing and the gate
threshold voltage. Reducing the amplitude will reduce the duty
cycle, but also lengthen the switching time and reduces the "peak
on bias." This will increase "DC on" losses.
[0010] In general, it is desirable to switch the controlled device
off as fast as possible. As frequencies are increased, a greater
portion of the switching period is required for the switching
transition, thus requiring a shorter conduction time, which is
shorter than can be achieved by known circuits.
[0011] Thus, there exists a need for a system having a drive
circuit capable of effectively operating (i.e., no or nominal loss
in power) over a greater range of duty cycles (i.e., about 25
percent to about 50 percent), and in particular, to such a system
for driving gated power devices (e.g., MOS devices) over this
greater range at higher frequencies. Such a system needs to control
the duty cycle without requiring the reduction of source amplitude
to unacceptable levels at these higher frequencies.
SUMMARY OF THE INVENTION
[0012] The present invention generally provides a half sine wave
drive circuit and method of providing the same having independent
adjustment of amplitude and duty cycle that recirculates or
recycles the energy involved in switching the input capacitance of
the driven device (e.g., MOS gated power device). Thus, the power
dissipation of the device is reduced and overall efficiency
increased, particularly at higher frequency operation (i.e., more
than a few hundred KHz). In operation the present invention
provides duty cycles of between about 25 percent and about 50
percent without loss of device power (i.e., no switching loss) at
higher switching frequencies.
[0013] Specifically, a drive circuit for use in connection with a
power device (e.g., MOS gated power device) includes switching
means for providing effective operation over a greater duty cycle
range, and a gate drive means for producing from a square wave
input signal a half sine wave output signal for use as a drive
voltage to the switching means to produce the greater duty cycle
range. The gate drive means includes a resonant circuit capacitivly
coupled to a gate of the switching means.
[0014] The switching means may be a transistor with the gate drive
means providing the half sine wave output signal to the gate of the
transistor. The resonant circuit is adapted to be configured
between the operating frequency of the input signal and about twice
the operating frequency to thereby provide a duty cycle of between
about 50 percent and about 25 percent. Essentially, a driver
inductance and capacitance of the resonant circuit are adapted to
be configured to control the duty cycle based upon a drive
frequency. The driver inductance of the resonant circuit may
comprise a transformer, and in this construction, may be adapted to
be configured to provide a duty cycle of between about 50 percent
and about 75 percent.
[0015] A DC bias means further may be provided to control the DC
level of the circuit. The resonant circuit may comprise, for
example, a class E single ended resonant circuit capacitivly
coupled to the gate of the switching means. A hard switch, such as
a logic gate, may be included for providing the input signal. The
relatively low power required at this input results in the power
lost, and hence dissipation, in the logic gate to not be
excessive.
[0016] In another embodiment, a resonant drive circuit of the
present invention providing improved independent amplitude and duty
cycle control without loss of power at higher operating frequencies
includes a MOS controlled device (e.g., transistor) to be switched
to provide a duty cycle of between about 25 percent and about 50
percent. A resonant drive circuit capacitivly coupled to a gate of
the MOS controlled device is also included and provides from a
square-wave input signal, a half sine wave output signal for
driving the MOS controlled device. The resonant drive circuit is
adapted for operation between an operating frequency of a driven
device (e.g., MOS gated power device) and about twice the operating
frequency, defined by the input signal.
[0017] A driver inductance and capacitance of the resonant drive
circuit are configurable to provide the duty cycle of between about
25 percent and about 50 percent. A DC bias may be provided to
control the DC level of the half sine wave signal. The resonant
circuit may include a transformer for providing the driver
inductance. A hard switched input device may be included for
providing the input signal.
[0018] A method of the present invention for controlling the
amplitude and duty cycle of a drive circuit without losing power at
higher operating speeds includes receiving a square wave input
signal, producing a half sine wave output signal from the square
wave input signal using a resonant circuit capacitivly coupled to a
switching a device, and configuring the resonant circuit to operate
at a duty cycle of between about 25 percent and about 50 percent.
DC bias also may be provided to the resonant circuit.
[0019] The method further may include recycling through the
resonant circuit a gate charge of the device being switched. A
transformer also may be used in connection with the resonant
circuit to add isolation or invert the drive waveform for 50 to 75
percent duty operation.
[0020] Thus, the present invention provides a resonant drive
circuit and method of providing the same that is capable of
operation over a greater duty cycle range (i.e., from about 25
percent to about 50 percent) without experiencing power loss at
higher frequencies. Through the adjustment of components within the
resonant circuit, an appropriate duty cycle may be provided for
driving a switching device, such as, for example, a MOS gated power
device.
[0021] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiments of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0023] FIG. 1 is a schematic diagram of a typical full sine wave
drive circuit;
[0024] FIG. 2 is a schematic diagram of another typical full sine
wave drive circuit;
[0025] FIG. 3 is a schematic diagram of a half sine wave drive
circuit constructed according to the principles of the present
invention;
[0026] FIG. 4 is a schematic diagram of the half sine wave drive
circuit of FIG. 3 with DC bias;
[0027] FIGS. 5(a) and 5(b) are graphs showing sine wave signals
produced by the half sine wave drive circuits of FIGS. 3 and 4;
[0028] FIGS. 6(a)-6(c) are graphs showing driver voltages produced
by the half sine wave drive circuit of the present invention;
[0029] FIG. 7 is a schematic diagram of another construction of a
half sine wave drive circuit of the present invention with
transformer coupling; and
[0030] FIG. 8 is a schematic diagram of a half sine wave drive
circuit of the present invention providing operation at 13.56
MHz.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The following description of the preferred embodiments is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses. Thus, although the application
of present invention as disclosed herein is generally directed to a
resonant drive circuit having a specific configuration for use in
driving a particular device, it is not so limited, and other
configurations for driving different devices may be provided in
accordance with the present invention.
[0032] In a typical resonant drive circuit as shown in FIGS. 1 and
2, and generally indicated by reference numeral 20 therein, a full
sine wave resonant drive circuit is provided for use in connection
with, for example, a MOS device. In particular, a transformer in
combination with a series resonant circuit 24, provides sinusoidal
outputs based upon a square wave voltage input signal. The
sinusoidal outputs are used to control switching devices 26, which
as shown, are insulated-gate field-effect transistors, which are
typically provided in a half-bridge configuration. It should be
noted that other types of transistors may be implemented depending
upon the particular application and drive requirements.
[0033] The outputs of the switching devices 26 are combined and
provided to the output network transformer, etc. Essentially, a
transformer-coupled push-pull operation (e.g., push-pull amplifier)
is provided, and may be used, for example, in power conversion
applications. It should be noted that other configurations are
possible, including, for example, parallel connection. In
operation, in order to change the duty cycle in the drive circuits
20 shown in FIGS. 1 and 2, which is accomplished by changing the
length of "dead time" or transition time between turning off one
switching device and turning on the other switching device, the
amplitude of the input signal to each of the switching devices must
be reduced. This may result in unacceptable operating voltages,
thus resulting in improper operation of the driven device,
particularly at higher operation frequencies (i.e., greater than
100 KHz).
[0034] Having described typical full sine wave drive circuits which
have limited control of duty cycle because of power problems,
particularly at higher frequencies, the present invention generally
provides a half sine wave resonant drive circuit having a greater
range of control of duty cycle without requiring a lower amplitude
(i.e., loss of power), including at higher operating frequencies.
In operation, a half sine wave output is provided to a single
switching device to control operation of that driven device (e.g.,
MOS gated power device).
[0035] In particular, and referring to one exemplary construction
of a half sine wave drive circuit configured according to the
principles of the present invention, such a drive circuit is shown
in FIG. 3 and indicated generally therein by reference numeral 30.
As shown therein, a class E single ended resonant circuit 32 is
capacitivly coupled to the gate 34 of a power switching device 36
(e.g., insulated-gate field-effect transistor).
[0036] Generally, in operation, a square wave voltage signal input
38 is provided to a driver switching device (Q1) 40 (e.g.,
transistor) with the drive circuit 30 of the present invention
producing a positive half sine wave signal 42 at the gate terminal
34 of the power switching device 36. The positive half sine wave
signal 42 has a period that is proportional to the resonant
frequency defined by a driver inductance (i.e., inductor L) 44, a
capacitance (i.e., capacitor C) 46, a coupling capacitance (i.e.,
capacitor C.sub.BL) 48 and a driven gate capacitance (i.e.,
capacitor C.sub.gs) 50. The positive half sine wave signal may be
provided at between about the operating resonant frequency and
about twice the operating resonant frequency based upon the square
wave voltage signal input 38 frequency to thereby provide a duty
cycle of between about 50 percent and about 25 percent. The driver
switching device (Q1) 40 in this exemplary construction experiences
normal zero voltage switching class E conditions, and thus
experiences no switching loss. All the gate charge is recycled
between the gate terminal 34 and driver supply stored in the supply
decoupling capacitor (Cd) 41.
[0037] With the gate terminal 34 capacitivly coupled to the
resonant circuit 32, the positive and negative volt/seconds will
balance, resulting in some negative off bias. Additional DC bias
can be added to counteract the negative off bias so as to maximize
the positive AC swing. For example, and as shown in FIG. 4, a
resistance (i.e., resistor R) 52 may be provided for coupling any
DC bias or grounding leaking currents. As shown in FIG. 5(a), the
half sine wave signal 42 produced by the drive circuit 30 may have
a negative component 54, as the DC level of the circuit is
undefined due to the capacitive coupling. With the addition of
appropriate resistance 52 (i.e., to compensate for negative off
bias), the negative component 54 can be reduced or virtually
eliminated to produce a half sine wave signal 42' as shown in FIG.
5(b).
[0038] The driver switching device (Q1) 40 is typically driven with
an approximately 50:50 duty cycle in a known manner. However, in
operation, this does not force the driver switching device (Q1) 40
output to switch at 50:50. As shown in FIGS. 6(a)-6(c), during the
cycle after the voltage has fallen to zero, indicated as t1 at 56,
the driver switching device (Q1) 40 reverse conducts, thereby
returning the resonant energy to the driver switching device (Q1)
40 supply stored in Cd 41. Thus, it is only necessary for the
driver switching device (Q1) 40 to be turned on at some point
before all this energy is recovered.
[0039] In an alternate construction of a half sine wave drive
circuit 30' as shown in FIG. 7, the driver inductance 44 may be
configured as a transformer 58 to add isolation between the driver
switching device (Q1) 40 and an output device. This construction
may also provide phase inversion for duty cycles of typically
between about 50 percent and about 75 percent with a negative half
sine signal. Alternately, a driver switching device (Q1) 40 with
the opposite polarity may be used.
[0040] As a further specific example of a half sine wave drive
circuit 30 constructed according to the principles of the present
invention, and to more clearly show such a circuit having
particular operating characteristics, FIG. 8 shows a half sine wave
drive circuit 30" constructed for operation at 13.56 MHz. As shown
therein, inductors (L1) 60 resonate with the capacitance of the
gates 66 of the STP10NB20 transistors 62 via the 690 pF capacitors
64 to produce a half sine pulse at approximately 18 MHz (i.e.,
about a 38 percent duty cycle). DC bias is applied to the gates 66
via the 1K resistors 68 and 4K7 70, forming a potential
divider.
[0041] A start up supply is bled from the main DC rail via the 47K
resistors 72. Charge stored in the 47 uF capacitors 74 begins drive
operation until the output swing has built up enough amplitude to
supply power via the two turn windings on inductor (L2) 76 and the
1DQ06 diodes 78. The current into the inductor (L2) 76 facilitates
switching the output capacitance of the STP10NB20 62. The IRF510s
transistors 80 are driven sinusoidaly in antiphase by transformers
(T1) 82, with their gate capacitance resonated out by inductor (L3)
84 at the input.
[0042] Thus, the present invention provides a half sine wave
resonant drive circuit having independent amplitude and duty cycle
control over a greater duty cycle range (i.e., about 25 percent to
about 50 percent) by providing short enough duty cycles to allow
enough time for output capacitance charging/discharging, thereby
resulting in efficient switching. As disclosed herein, the
invention is particularly well suited for operation at higher
frequencies (e.g., 10+ MHz). For example, operation at a greater
range of duty cycles is particularly adapted for use in high
frequency half bridge circuits wherein significant dead time is
needed between alternate conduction to cycle the output capacitance
of the bridge device. It should be noted that the half sine wave
signal normally contains significant harmonics, and as such, any
transformer provided in connection with the present invention must
have enough high frequency performance and bandwidth to reliably
pass these harmonics.
[0043] Although the present invention has been described in
connection with specific component parts operating at specific
frequencies, it is not so limited. For example, in constructing a
half sine wave drive circuit 30 according to the present invention,
the inductance 44, capacitance 46 and capacitance 48 may be
adjusted to obtain the desired gate 34 swing for a particular
driver DC voltage and driver device swing. Further, the driven
device may be any MOS controlled device such as a MOSFET, IGBT,
etc. Additionally, the driver device may be MOS controlled or
bipolar and include an anti parallel diode to provide reverse
conduction.
[0044] The description of the invention is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the invention are intended to be within the scope of the invention.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention as claimed.
* * * * *