Electricity: power supply or regulation systems – Input level responsive – Using a linearly acting final control device
Reexamination Certificate
2000-05-30
2001-02-06
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Input level responsive
Using a linearly acting final control device
C323S273000, C323S277000, C323S908000
Reexamination Certificate
active
06184669
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current control circuit, disposed between a primary terminal and a secondary terminal, for controlling a current flowing from the primary terminal to the secondary terminal.
2. Description of the Related Art
Hitherto, there is known a rush current preventing circuit, disposed between a source output terminal of a power supply and a source input terminal of an arbitrary electronic circuit, for preventing a rush current so that an output of the power supply does not exceed a predetermined rated output.
Further, there is known an overcurrent detection circuit for detecting an overcurrent to prevent fumes and going up in flames from occurring even if the electronic circuit of the secondary is subjected to a short-circuit and the like, while a sufficient current is supplied even if the maximum load is involved within a usual operating range of the electronic circuit of the secondary.
FIG. 4
is a circuit diagram of a current control circuit according to an embodiment of the present invention. a circuit diagram showing a state that both the rush preventing circuit and the overcurrent detection circuit are provided.
Usually, a considerably large capacity of capacitor C is disposed at the secondary. At the time of a power supply is turned on, a rush current will occur for a charge of the capacitor C and the like. The rush preventing circuit is disposed to prevent the primary power supply from being damaged by the rush current. Further, the overcurrent detection circuit is connected in series to the rush preventing circuit to prevent an overcurrent from conducting when an electronic circuit connected to the secondary is subjected to a short-circuit and the like. When the overcurrent detection circuit detects the overcurrent, a detection result is transmitted to an overcurrent recognition circuit (not illustrated). Thus, the overcurrent recognition circuit recognizes that the overcurrent, which is not to be accepted, conducts. And then the overcurrent is suppressed by an overcurrent control circuit (also not illustrated).
According to the circuit constitution as shown in
FIG. 4
, both the rush preventing circuit and the overcurrent detection circuit are provided on a current path directed from the primary to the secondary. This constitution brings about power loss on the respective circuits and voltage drop at the secondary. This causes shortage of ability in operation for the electronic circuits connected to the secondary, or alternatively increments of a circuit scale and a circuit cost for suppressing power loss on the rush preventing circuit and the overcurrent detection circuit to avoid the occurrence of the shortage of ability in operation for the electronic circuits.
Individual provision of the rush preventing circuit and the overcurrent detection circuit as shown in
FIG. 4
brings about necessity for design and test of respective circuits. This involves an increment of process.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a current control circuit for controlling a current flowing from the primary to the secondary, the current control circuit being capable of reducing power loss and voltage drop.
To achieve the above-mentioned object, the present invention provides a current control circuit, disposed between a primary terminal and a secondary terminal, for controlling a current flowing from the primary terminal to the secondary terminal, said current control circuit comprising:
a first resistance disposed on a current path directed from the primary terminal to the secondary terminal;
a MOSFET, in which its drain and source are connected in series to said first resistance, disposed between said first resistance and the secondary terminal, said MOSFET permitting a maximum permissible current or less current to conduct in accordance with a voltage applied to its gate;
a PNP transistor in which its emitter is connected to a primary of said first resistance and its base is connected to the secondary of said first resistance; and
a voltage drop device, disposed between the collector of said PNP transistor and the gate of said MOSFET, for supplying to the gate of said MOSFET a voltage dropped by a predetermined potential from a voltage of the collector of said PNP transistor.
According to the current control circuit of the present invention as mentioned above, when a current flows through the first resistance, there is generated a voltage between the primary and the secondary of the first resistance, which voltage is proportional to the current thus flowed. This voltage makes it possible to derive as an overcurrent detection signal a signal outputted from the collector of the PNP transistor when the PNP transistor turns on. Further, when the overcurrent occurs, the voltage drop device connected to the collector of the PNP transistor causes a gate-to-source voltage of the MOSFET disposed between the first resistance and the secondary terminal to be lowered, and thus the drain current is subjected to a constant current control with a somewhat larger current value than the overcurrent detection current.
In this manner, according to the current control circuit of the present invention, simply disposing one resistance (the first resistance) and one MOSFET between the primary terminal and the secondary terminal makes it possible to implement a circuit capable of performing both the overcurrent detection and the rush current prevention, through suppressing power loss and voltage drop to the minimum.
In the current control circuit of the present invention as mentioned above, it is preferable that said voltage drop device is a diode of which an anode is connected to the collector of said PNP transistor. Or alternatively, it is acceptable that said voltage drop device is a Zener diode of which a cathode is connected to the collector of said PNP transistor.
In the current control circuit of the present invention as mentioned above, it is preferable that a capacitor is connected in parallel to said voltage drop device.
In the event that a large capacity of capacitor is connected to the secondary, when the power supply of the primary turns on, or when the motor of the secondary is activated, it happens that a current exceeding a set value flows transitionally owing to a delay in operational time of the voltage drop device. This problem is solved in accordance with the present invention. That is, connecting a capacitor in parallel to the voltage drop device makes it possible to reduce the response time and thereby suppressing generation of a transitional large current.
In the current control circuit of the present invention as mentioned above, it is preferable that a second resistance is connected between the base of said PNP transistor and the emitter of said PNP transistor, and the base of said PNP transistor is connected via a third resistance to a secondary of said first resistance. In this case, it is preferable that at least one of said second resistance and said third resistance is a variable resistance.
In some load of the secondary, there is a need to alter the criterion of the overcurrent to be regarded as it. Here, as the first resistance, in order to lower the voltage drop, there is used a resistance which is the low impedance and is high in heat capacity, and usually the sort of such a resistance is restricted. Therefore, it is not effective that the first resistance is altered whenever the secondary load is altered. For this reason, as mentioned above, the second resistance and the third resistance, which are connected in series to one another, are connected in parallel to the first resistance, so that a voltage is divided by the second resistance and the third resistance. This feature makes easy to alter the current value to be detected as the overcurrent. Here, the use of a variable resistance for the second resistance or the third resistance makes more easy to adjust the alteration.
In the current control circuit of the present inventi
Fujitsu Limited
Riley Shawn
Staas & Halsey , LLP
LandOfFree
Current control circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Current control circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Current control circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2585120