Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2002-01-31
2002-11-26
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S112000
Reexamination Certificate
active
06486714
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a half-bridge inverter circuit and, in particular, to a half-bridge inverter circuit to which a load driven at a high voltage is connected.
2. Description of the Related Art
A configuration of a half-bridge inverter circuit for lighting is shown in FIG.
1
. Q
1
and Q
2
denote main switching elements, each including a power MOSFET. D
1
and D
2
are resonance current-commutating diodes, each including a parasitic diode between the drain and source of the power MOSFET. In a ballast circuit, L denotes a resonance reactor, C
1
denotes a direct current component-cutting capacitor, C
2
denotes a filament-preheating capacitor, and a circuit configuration is provided such that a fluorescent lamp
3
is connected in parallel with the filament-preheating capacitor C
2
.
FIG. 2
shows operating waveforms when the lamp of the circuit of
FIG. 1
is on. VGS
1
and VGS
2
denote gate-source voltages of the main switching elements Q
1
and Q
2
, respectively. During operation, the main switching elements Q
1
and Q
2
are alternately repeatedly turned on and off, and in order to prevent the main switching elements Q
1
and Q
2
from simultaneously being turned on, dead time periods, during which both main switching elements Q
1
and Q
2
are off, are provided.
The high-side main switching element Q
1
is turned on when VGS
1
becomes high and a drain current shown by ID
1
flows. Thereby, a square wave voltage is applied to the ballast circuit composed of L, C
1
, C
2
and fluorescent lamp
3
, and a sine wave-shaped ballast current I
1
flows. The ballast current I
1
when the lamp is on is a composite current formed of a filament current I
2
and a lamp current I
3
.
The low-side main switching element Q
2
is turned on when VGS
2
becomes high and a drain current ID
2
flows. When that happens, energy which has been accumulated in the ballast circuit is discharged and the ballast current I
1
, the filament current
12
, and the lamp current
13
decrease in the negative direction.
In an ordinary half-bridge inverter circuit, operations are carried out at a frequency in a delayed phase band which is higher than a resonance frequency. Accordingly, since the ballast current I
1
can be changed by a switching frequency of the main switching elements Q
1
and Q
2
, it becomes possible to adjust brightness.
Referring to
FIG. 1
, an input signal from a control circuit
1
is converted to appointed drive signals (for example, VGS
1
and VGS
2
) at a drive circuit
2
, whereby the main switching elements Q
1
and Q
2
are driven.
A detailed circuit block of this drive circuit
2
is shown in FIG.
6
. This drive circuit
2
includes a signal input circuit
21
, dead time control circuits
22
and
23
which perform dead time control on the high side and the low side, respectively, a pulse generating circuit
24
, a level shifting circuit
25
, a pulse filter circuit
26
, a latch circuit including an RS flip-flop circuit
27
, and output circuits
28
and
29
which supply drive signals HO and LO for driving the main switching elements Q
1
and Q
2
on the high side and the low side.
In such a drive circuit
2
, an output signal from the control circuit
1
is shaped by the signal input circuit
21
, then inputted into the dead time control circuits
22
and
23
which perform dead time control on the high side and the low side, and as shown in
FIG. 7
, a high-side output signal HO, which is delayed from the input signal (output signal from the control circuit
1
), and a low-side output signal LO, which falls before the high-side output signal HO rises, are formed. For the high-side output signal HO and the low-side output signal LO, dead time periods are provided during which both become low level so that the main switching elements Q
1
and Q
2
are not simultaneously turned on.
In the drive circuit
2
on the high side, since the main switching element Q
1
is driven at a voltage of approximately 600V, it is necessary to form a drive signal VGS
1
by shifting the high-side output signal HO to a high voltage of approximately 600V. An output signal PGIN from the dead time control circuit
22
is inputted into the pulse generating circuit
24
and a set output signal OUT (Set) and a reset output signal OUT (Reset) are outputted therefrom. These signals are inputted into the subsequent level shifting circuit
25
for shifting to a high voltage and converted to a high-voltage set output signal OUT (Set) and a high-voltage reset output signal (Reset). These signals allow signals of a predetermined pulse width or longer to pass through the pass filter circuit
26
, thereby setting and resetting the latch circuit
27
, and a high side output signal HO is outputted from the output circuit
28
, thereby driving the main switching element Q
1
on the high side.
In such a half-bridge inverter circuit, in order to prevent the main switching elements Q
1
and Q
2
from simultaneously being turned on, dead times are provided during which both drive signals (for example, VGS
1
and VGS
2
) are off.
However, at a start-up time, it is uncertain whether a high-side output signal is first outputted from the drive circuit or a low-side output signal is first outputted therefrom, and therefore a stable start-up condition cannot be obtained. A problem exists that if the high-side output signal is first outputted, the main switching elements Q
1
and Q
2
are simultaneously turned on.
SUMMARY OF THE INVENTION
The present invention is provided to solve the foregoing problem such that at a start-up time two main switching elements simultaneously may turn to the on-mode, and provides a half-bridge inverter circuit including dead time control circuits on the high side and the low side which form dead time periods based on an input signal to be inputted from a control circuit, and a start-up circuit including a latch circuit, which is reset upon detection of a rise in power supply on the low side, then set by a low-side output signal from the dead time control circuit on the low side, and a gate circuit, which receives the low-side output signal in response to an output from the latch circuit, then allows a high-side output signal from the dead time control circuit on the high side to pass. This configuration prevents the two main switching elements from being simultaneously turned on at a start-up time.
According to the present invention, by providing the start-up circuit which prioritizes a low side signal, the main switching element on the low side is always first turned on at start-up. Thus, an advantage exists such that a stable start-up of the half-bridge inverter circuit can be performed.
REFERENCES:
patent: 4733104 (1988-03-01), Steigerwald et al.
patent: 5684686 (1997-11-01), Reddy
patent: 6002213 (1999-12-01), Wood
patent: 6081438 (2001-06-01), Saint-Pierre et al.
Ikeda Kenji
Saito Takaaki
Ushida Atsuya
Le Dinh T.
Morrison & Foerster / LLP
Sanyo Electric Co,. Ltd.
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