Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2002-09-24
2004-05-11
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S090000, C327S112000
Reexamination Certificate
active
06734706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit for driving a power device, and particularly to a technology operable to prevent false operation of the high potential side output associated with an false signal due to the negative noise and the like at the high potential side reference potential.
2. Description of the Related Art
FIG. 9
shows a configuration of a prior driving circuit for power devices. The driving circuit is connected to a power device such as the IGBT and MOSFET (not illustrated), and used to generate a control signal to drive the power devices. Such the driving circuit is described below.
The driving circuit illustrated in
FIG. 9
is equipped with a level shift circuit
10
′, a transmitter circuit
30
′, and a driver circuit
50
. The level shift circuit
10
′ includes resisters R
1
and R
2
, high-voltage field effect transistors (hereafter called “HNMOS transistor”) T
1
and T
2
. The transmitter circuit
30
′ has an RS flip-flop
31
, NOR gates
33
and
34
, NAND gates
35
and
36
, inverter gates
37
and
38
, and a mask signal circuit
40
c
including an AND gate. The driver circuit
50
is connected to a power device such as the IGBT and MOSFET, and its output signal controls the driving of the power device.
A signal on the high potential side that controls the ON and OFF operation of the power device is fed into the level shift circuit
10
′. The high potential side signal is a square wave signal, and is fed to the HNMOS transistors T
1
and T
2
of the level shift circuit
10
′ such that a level of the high potential side signal is shifted to a high potential. The level-shifted signals (hereafter referred to “ON signal” and “OFF signal”) are transmitted from the driver circuit
50
to the power device through the inverter gates
37
and
38
of the transmitter circuit
30
′.
In general, a load of the power device driven by the driving circuit can be an inductive load of a motor or a fluorescent lamp. Owing to an influence of such an inductive load and parasitic inductance components of wiring on a printed circuit board, the high potential side reference potential (potential at the grounding line
23
) in the driving circuit fluctuates to the negative side of the ground (potential at the grounding line
25
) during switching, so that the high potential side signal becomes false by this fluctuation. The false signal can be generated by dv/dt applied to the high potential side reference potential or by a large negative noise level in the high potential side reference potential.
The false signal causes a current to flow through level shift resistors R
1
and R
2
connected to the high potential side power supply
21
by parasitic capacitance or parasitic diodes of the HNMOS transistors T
1
and T
2
, and the like, thereby causing a voltage drop. Then the false signal is transmitted to the transmitter circuit
30
′, resulting in false operation of the power device.
The circuit illustrated in
FIG. 9
uses a logic filter technique to counteract the false operation. That is, the circuit has a mask signal circuit
40
c that generates a signal that cancels the false signal. The mask signal circuit
40
c
generates a signal (called “mask signal” hereafter) that masks the “ON” and “OFF” signals so that these signals are not transmitted to the RS flip-flop
31
if they are both active. The mask signal masks the “ON” and “OFF” signals input to the transmitter circuit
31
, that is, output signals (called “main signals” hereafter) of the NAND gates
35
and
36
. At this time, the operation ranges of the main signals and the mask signal are set to the same. However when their operation ranges are dispersed, the false signal may be transmitted to the transmitter circuit
31
. We now describe this situation referring to FIG.
10
.
For example, suppose the case where the outputs of level shift circuit
10
′, that is, the “ON” and “OFF” signals rapidly decline by the influence of dv/dt and the like as shown in FIG.
10
A. Also suppose that the level of the threshold values of the NAND gates
35
and
36
and the level of the threshold value for the mask signal circuit
40
c
are different by dispersion and the like. In
FIG. 10A
, the threshold values for the NAND gates
35
and
36
is illustrated by the broken line B′ and the level of the threshold value for the mask signal circuit
40
c
is illustrated by the broken line A′. In this case, the main signals and the mask signal respectively vary as shown in
FIGS. 10B and 10C
. More particularly, the range where the mask signal is active (i.e. HIGH) becomes narrower than the range where the main signals become inactive (i.e. LOW), so that a main signal that becomes falsely inactive, i.e. a false signal, can not be sufficiently masked. Therefore, a false signal occurs in a latch input signal which is a set input signal of the RS flip-flop
31
, as shown in FIG.
10
D.
SUMMARY OF THE INVENTION
The present invention is aimed to solve the above problem, and its object is thus to provide a driving apparatus for driving power devices operable to securely prevent an false signal due to negative noise, dv/dt and the like on the high potential side reference potential from occurring.
A driving circuit according to the present invention is a circuit for driving a power device including level shift circuit that shifts levels of main signals comprising ON and OFF signals that respectively instruct ON and OFF of the power device and outputs the shifted signals, transmitter circuit that latches the main signals to transmit to the power device, mask signal circuit that generates a mask signal based on the main signals, the mask signal preventing the main signals from transmitting when the logic of the “ON” and “OFF” signals becomes the same to cause false operation, and potential difference adding circuit that provides a potential difference between a signal as the main signal fed to the mask signal circuit and a signal as the main signal fed to the transmitter circuit. Therefore, the operation range of the mask signal is enlarged, and the false signal can be masked more securely, so that the occurrence of the false signal can be securely prevented.
In the driving circuit, the mask signal circuit may generate a mask signal to cancel one of the main signals from a signal obtained by inverting the other of the main signals. Therefore, it does not require to adjust with high precision threshold values, delay time, and so on of logic gate elements involved in the mask signal path and the main signals path, so that design efficiency can be improved. Further, the signal circuits can be simplified.
Further, the potential-difference adding circuit may include a resistor element, and bias current can be reduced by appropriately determining the resistance value of the resistor element. Therefore, a heat loss which is a latent problem in driving circuits can be improved.
Further, the potential-difference adding circuit may include a PMOS transistor, and the threshold voltage can be increased by using the back-gate effect. In that case, there is an advantage when the potential difference &Dgr;V is set at a large value.
Further, the potential-difference adding circuit may include an NMOS transistor. In that case, the potential difference &Dgr;V is less affected by current, so that the potential-difference value becomes more stable. Therefore, the operation range of the main signals and the operation range of the mask signal can be stably separated.
Further, the potential-difference adding circuit may include a diode. In that case, the value of the potential difference &Dgr;V can be more finely set with a plurality of stages of diodes.
Further, the potential-difference adding circuit may include a Zener diode. In that case, a large value of the potential difference &Dgr;V can be obtained with a single-stage of Zener diode, so that the layout area can be reduced.
REFERENCES:
patent: 4638187 (1987-01-01), Boler et al.
patent:
Tanaka Yoshikazu
Yoshida Hiroshi
Lam Tuan T.
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Hiep
LandOfFree
Circuit for driving a power device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit for driving a power device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit for driving a power device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3209372