Electricity: power supply or regulation systems – In shunt with source or load – Using a three or more terminal semiconductive device
Reexamination Certificate
2000-07-07
2001-11-13
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using a three or more terminal semiconductive device
Reexamination Certificate
active
06316922
ABSTRACT:
BACKGROUND
FIG.
28
(
a
) is a block circuit diagram of a first conventional switching DC-DC converter of step-down type. As shown in the figure, a smoothing capacitor Cin for smoothing a DC input voltage Vin, a main switching transistor
1
as a main switching semiconductor device for connecting and disconnecting the DC input voltage Vin, a freewheel diode
11
, a coil L, a capacitor Cout, a control circuit
3
, a gate driver (hereinafter referred to simply as a “driver”)
2
, and passive components
4
are provided. In FIG.
28
(
a
), the main switching transistor
1
is a p-channel MOSFET.
The freewheel diode
11
provides a load current path when the main switching transistor
1
is OFF. The coil L and the capacitor Cout are disposed to smooth an output voltage Vout from the DC-DC converter.
The input voltage Vin is connected, as a power supply, to the control circuit
3
and the driver
2
. The control circuit
3
detects the output voltage Vout and outputs a control signal
3
a
for setting the timing of switching on and off the main switching transistor
1
to keep the output voltage Vout at a certain value. The driver
2
outputs a drive signal
2
a
in response to the control signal
3
a
from the control circuit
3
to directly switch on and off the main switching transistor
1
.
Various attached passive components for the control circuit
3
are collectively represented by the passive components
4
in FIG.
28
(
a
). For example, a capacitor for smoothing the output of the constant voltage source in the control circuit
3
, a resistor and a capacitor for setting the oscillator frequency in the control circuit
3
are included in the passive components
4
.
FIG.
28
(
b
) is a block circuit diagram of a second conventional switching DC-DC converter of step-down type. FIG.
28
(
b
) shows only a part of the second conventional DC-DC converter different from the corresponding part of the first conventional DC-DC converter. The second conventional DC-DC converter is different from the first conventional DC-DC converter in that the freewheel diode
11
of FIG.
28
(
a
) is replaced by a synchronous commutation transistor
12
formed of an N-channel MOSFET in FIG.
28
(
b
).
The synchronous commutation transistor
12
is switched off and on in response to the drive signal
2
b
from the driver
2
synchronizing with the ON and OFF of the main switching transistor
1
to provide a load current path when the main switching transistor
1
is OFF.
Since the on-voltage of the transistor may be set lower than the forward voltage drop across the diode, the synchronous commutation transistor
12
used in substitution for the freewheel diode
11
facilitates improving the efficiency of the switching DC-DC converter.
FIG. 29
is a block circuit diagram showing a circuit configuration that integrates the main switching transistor
1
, the driver
2
and the control circuit
3
of FIG.
28
(
a
) in a one-chip semiconductor integrated circuit (hereinafter referred to as a “one-chip IC”)
100
.
In the circuit configuration shown in
FIG. 29
, the operation of the converter becomes unstable when the load is heavy, presumably because the control circuit malfunctions due to an increase of the switching noise caused by load current increase, and it becomes impossible for the converter to operate properly as the switching frequency increases.
The conditions are worse for the DC-DC converter shown in FIG.
28
(
b
) that incorporates the synchronous commutation transistor
12
in the one-chip IC
100
, since the switching noise from the synchronous commutation transistor
12
is added.
In view of the foregoing, it is an object of the invention to provide a DC-DC converter, including a main switching transistor, a driver and a control circuit incorporated in a one-chip IC, that facilitates preventing switching noises, caused by a heavily load or by high-speed switching, from affecting the control circuit adversely and securing stable operations of the control circuit.
SUMMARY OF THE INVENTION
The invention provides a switching DC-DC converter including: a one-chip semiconductor integrated circuit; the one-chip semiconductor integrated circuit including at least a main switching semiconductor device including main terminals and a control terminal (gate), the main switching semiconductor device periodically switching on and off to periodically connect and disconnect a DC power supply, the main switching semiconductor device feeding an output voltage to a load; a control circuit fed from the DC power supply, the control circuit detecting the output voltage outputted from the main switching semiconductor device, the control circuit outputting a control signal indicating the timing of switching on and off the main switching semiconductor device; and a first drive circuit fed from the DC power supply, the first drive circuit feeding a drive signal for directly switching on and off the main switching semiconductor device to the control terminal of the main semiconductor switching device in response to the control signal; the switching DC-DC converter is characterized by inclusion of: a positive feed line and a negative feed line connecting the DC power supply to the control circuit including attached passive components thereof; and a resistor inserted in the positive feed line or in the negative feed line inside or outside the semiconductor integrated circuit, the resistor preventing a noise current from flowing into the control circuit.
Advantageously, the switching DC-DC converter further includes another resistor inserted in the negative feed line or in the positive feed line inside or outside the semiconductor integrated circuit, the other resistor preventing the noise current from flowing into the control circuit.
Advantageously, the switching DC-DC converter further includes a commutation switching semiconductor device in the one-chip semiconductor integrated circuit, the commutation switching semiconductor device including main terminals and a control terminal (gate), one of the main terminals (drain) of the commutation switching semiconductor device being connected to the load-side one (drain) of the main terminals of the main switching semiconductor device, the commutation switching semiconductor device being switched off and on in synchronism with the switching on and off of the main switching semiconductor device to provide a load current path when the main switching semiconductor device is OFF; and a second drive circuit in the one-chip semiconductor integrated circuit, the second drive circuit being fed from the DC power supply, the second drive circuit feeding a drive signal indicating the switching off and on of the commutation switching semiconductor device to the control terminal (gate) of the commutation switching semiconductor device.
Advantageously, the switching DC-DC converter further includes a capacitor disposed inside or outside the semiconductor integrated circuit, the capacitor dividing the noise current, the capacitor being connected between the positive feed line and the negative feed line without any of the resistors interposed between the capacitor and the feed lines.
Advantageously, the positive feed line or the negative feed line connects the resistor incorporated in the semiconductor integrated circuit to the control circuit without any lead-out terminal of the semiconductor integrated circuit interposed between the control circuit and the resistor.
Advantageously, the positive feed line and the negative feed line connect the respective resistors incorporated in the semiconductor integrated circuit to the control circuit without any lead-out terminal of the semiconductor integrated circuit interposed between the control circuit and the resistors.
Advantageously, the capacitance of the capacitor is the parasitic capacitance of the semiconductor integrated circuit.
The switching DC-DC converter according to the invention inserts an insulation resistor (filter resistor) between a feed line, to which a main switching transistor, a driver and, if necessary, a synchronou
Katayama Yasushi
Sugahara Satoshi
Fuji Electric & Co., Ltd.
Riley Shawn
Rossi & Associates
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