Electrical transmission or interconnection systems – Switching systems – Condition responsive
Patent
1996-10-30
1999-09-14
Gaffin, Jeffrey
Electrical transmission or interconnection systems
Switching systems
Condition responsive
307125, 307139, H01H 3500
Patent
active
059527404
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a load drive device wherein the load is driven with intermittent voltage applied to the load or with the current controlled; in particular, it relates to a load drive device of simple construction and high reliability.
BACKGROUND ART
Conventionally, as a load drive device wherein an inductive load such as for example the coils of a solenoid plunger or stepping motor were driven, a device has been employed whereby the mean voltage or mean current applied to the load is controlled by opening and closing a circuit opening/closure means inserted between this load and the power source and consisting of a semiconductor switch or the like. This device is known as a chopper control or PWM (pulse width modulation) control, and a typical conventional circuit layout is shown in FIG. 11 and FIG. 12.
The circuit shown in FIG. 11 is of a circuit construction called a high side switch for switching current on the power source side of the load; the circuit shown in FIG. 12 has a circuit construction called a low side switch that switches current on the earthed side of the load.
FIG. 11 is constituted by providing two transistors TR1, TR2 constituting switch means and two resistors R0, R1; a PWM signal of predetermined duty ratio is applied to the base of transistor TR1, a power source is connected to the emitter of transistor TR2; resistor R0 is connected between the emitter and base of transistor TR2; resistor R1 is connected between the collector of transistor TR1 and the base of transistor TR2; and the emitter of transistor TR1 is earthed. Also, a flywheel diode FD is connected in parallel with the inductive load L that is the subject of drive by this circuit; the cathode of flywheel diode FD is connected to the collector of transistor TR2; and the anode of flywheel diode FD is earthed.
With such a construction, when the PWM signal becomes high level, turning transistor TR1 ON, in response to this, transistor TR2 is turned ON, and the power source is applied to load L through transistor TR2, so that load current flows to earth from the power source through transistor TR2 and load L. When this happens, due to the characteristic of the load L, this load current increases with time, finally becoming constant at a saturation point given by the power source voltage and the amount of resistance, not shown, in inductive load L.
However, when chopper control is exercised, with the object of controlling the mean current flowing in the load, the mean current value required in load L is lower than the current value at the saturation point, so, before the load current flowing in load L reaches this saturation point, the PWM signal goes from high level to low level, causing transistor TR1 to go from ON to OFF and transistor TR2 also to go from ON to OFF, cutting off the power source from load L.
In this connection, the ON/OFF timing of transistor TR2, i.e. the timing of high level/low level of the PWM signal is determined by for example ON/OFF ratio control (duty control) of transistor TR2 based solely on the time or by detecting the load current flowing in load L by means of a current detector, not shown, in accordance with a predetermined standard such as constant-current control based on its instantaneous value or mean value.
In either case, when transistor TR2 turns OFF and the power source is cut off from load L, the load current flowing in load L flows back through flywheel diode FD due to the inductive component of load L, and is gradually decreased by the electrical resistance of the circuit and the forward voltage of the flywheel diode FD.
In this condition, when the PWM signal again goes from low level to high level, causing transistor TR1 to turn ON and transistor TR2 to turn ON, the power source is once more connected to load L and the load current flowing in load L progressively increases as described earlier.
Thus, with this high side switch, the ON/OFF timing of transistor TR2 is altered by means of the ON/OFF timing of the PWM signal applied to the base of transis
REFERENCES:
patent: 4473784 (1984-09-01), Morez
patent: 4873453 (1989-10-01), Schmerda et al.
patent: 5523632 (1996-06-01), Seragnoli
patent: 5539610 (1996-07-01), Williams et al.
N. Kumagai, "Gate Operation Circuit Configuration with a Power Supply for MOS-Gate Devices", Proceedings of 1992 International Symposium on Power Semiconductor Devices & IC's, Tokyo, May 19-21, 1992, pp. 194-197.
Kato Koichi
Kawaji Yasushi
Maeda Kenichiro
Yoshida Daisuke
Gaffin Jeffrey
Kaplan Jonathan
Komatsu Ltd.
LandOfFree
Load drive 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 Load drive device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Load drive device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1512670