Electricity: power supply or regulation systems – In shunt with source or load – Using a three or more terminal semiconductive device
Reexamination Certificate
2000-09-28
2001-11-20
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using a three or more terminal semiconductive device
C323S282000, C323S283000, C323S287000, C323S270000
Reexamination Certificate
active
06320359
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a DC-DC converter, and more particularly, to a synchronous rectifier type DC-DC converter used as a power source for electronic devices and a controller for such DC-DC converter.
The recent increase in the operational frequency speed of a CPU for electronic devices has resulted in an increase in the power source current. This, in turn, has increased the power of a synchronous rectifier type DC-DC converter, which is used as a power source of the CPU. In a DC-DC converter, a main switching device and a synchronous switching device, which are connected in series, are alternately activated and deactivated to supply a constant voltage to a load. When these switching devices are short-circuited, an amount of current greater than that during normal operation may flow toward other externally connected devices and damage the externally connected devices. Accordingly, it is required that the externally connected devices be protected.
FIG. 1
is a schematic circuit diagram of a prior art DC-DC converter
1
. The DC-DC converter
1
includes a controller
2
, which is formed as a circuit on a single semiconductor substrate, and a plurality of externally connected devices, that is, a main switching device
3
, a synchronous switching device
4
, a choke coil
5
, a flyback diode
6
, and a smoothing capacitor
7
.
The controller
2
provides the main switching device
3
with a first drive signal SG
1
. The switching device
3
is an enhancement n-channel MOS transistor, which gate is provided with the drive signal SG
1
. The drain of the switching device
3
is supplied with power source voltage Vi from a battery E. The source of the switching device
3
is connected to the synchronous switching device
4
.
The synchronous switching device
4
is an enhancement n-channel MOS transistor having a drain connected to the source of the main switching device
3
. The gate of the synchronous switching device
4
is provided with a second drive signal SG
2
from the controller
2
and the source is connected to the ground GND.
The source of the main switching device
3
is connected to an output terminal To via the choke coil
5
, and also to the cathode of the flyback diode
6
, which anode is connected to the ground GND.
The output terminal To is connected to the ground GND via the smoothing capacitor
7
and to a load (not shown), such as a CPU. The output terminal To provides the load with an output voltage Vo and returns the output voltage Vo to the controller
2
.
With reference to
FIG. 2
, the controller
2
provides the switching devices
3
,
4
respectively with first and second drive signals SG
1
, SG
2
, which are essentially complementary signals. This alternately activates and deactivates the main switching device
3
and the synchronous switching device
4
. The switching of the main switching device
3
fluctuates the voltage VS at a node N
1
between the two switching devices
3
,
4
in a pulse-like manner. The voltage VS is smoothed by the choke coil
5
and the smoothing capacitor
7
to generate a predetermined output voltage Vo.
The controller
2
compares the returned output voltage Vo with a reference voltage to vary the duty ratio of the first and second drive signals SG
1
, SG
2
. This enables the DC-DC converter
1
to substantially match the output voltage Vo with a set voltage.
When the main switching device
3
is deactivated, the synchronous switching device
4
is activated. This maintains the voltage drop of the voltage VS, which is caused by the forward voltage VD of the flyback diode
6
, at substantially zero volts. Thus, the synchronous switching device
4
suppresses power consumption by the flyback diode
6
and prevents the smoothing efficiency from being decreased. This improves the efficiency of the DC-DC converter
1
. Thus, the synchronous rectifier DC-DC converter
1
is used in equipment that requires a large output current.
However, when a short-circuit occurs between the drain and the source of the main switching device
3
, the output voltage Vo becomes higher than the set voltage. Since such short-circuit results in an abnormal output, a protection measure has been provided in the prior art.
When a short-circuit occurs between the gate and source of the synchronous switching device
4
, the switching device
4
is deactivated. Thus, the DC-DC converter
1
operates as a normal DC-DC converter, which does not have the synchronous rectifying function, and the output voltage is almost the same as that during a normal state. However, the rating of each of the devices
3
-
7
is set as for a synchronous rectifier type DC-DC converter. Thus, the load applied to the main switching device
3
and the flyback diode
6
increases, which may, in turn, produce heat and damage the devices. Such problem is especially prominent in a DC-DC converter having a large output current.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a DC-DC converter and a controller for a DC-DC converter that protects devices when an abnormality occurs in a synchronous switching device.
To achieve the above object, the present invention provides a controller for controlling a DC-DC converter. The DC-DC converter includes a main switching device and a synchronous switching device, which are series-connected, and a flyback diode and a smoothing circuit, which are connected to a node between the switching devices. The controller includes a drive control circuit for alternately activating and deactivating the main switching device and the synchronous switching device by supplying the main switching device with a first drive signal and the synchronous switching device with a second drive signal. A signal control circuit detects malfunction of the synchronous switching device and upon detection of a malfunction, controls the drive control circuit to inhibit the supply of the first and second drive signals.
Another aspect of the present invention provides a controller for a DC-DC converter. The DC-DC converter includes a main switching device and a synchronous switching connected in series between a power supply and a ground. The controller includes a drive control circuit for supplying a first drive signal to the main switching device and a second drive signal to the synchronous switching device to alternately activate and deactivate the main switching device and the synchronous switching device. A detection circuit is connected to the synchronous switching device for detecting a malfunction thereof and generating a detection signal. A protection circuit, connected to the detection circuit and the drive control circuit, inhibits the first and second drive signals in response to the detection signal. The controller is formed on a single semiconductor substrate.
A further aspect of the present invention provides a DC-DC converter including a main switching device, a synchronous switching device connected in series with the main switching device, a flyback diode connected to a node between the two switching devices, a smoothing circuit connected to a node between the two switching devices, and a controller connected to the main switching device and the synchronous switching device. The controller includes a drive control circuit for alternately activating and deactivating the main switching device and the synchronous switching device by supplying the main switching device with a first drive signal and the synchronous switching device with a second drive signal. A signal control circuit detects a malfunction of the synchronous switching device and upon detection of the malfunction, controls the drive control circuit to inhibit the supply of the first and second drive signals.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 5705919 (1998-01-01), Wilcox
patent: 5731694 (1998-03-01), Wilcox et al.
patent: 599488
Inatomi Koichi
Matsuyama Toshiyuki
Nagaya Yoshihiro
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Limited
Riley Shawn
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