Constant-current controller for an inductive load

Patent metadata

Field	Value
Publication number	US-2016307683-A1
Application number	US-201615098522-A
Country	US
Kind code	A1
Filing date	Apr 14, 2016
Priority date	Apr 14, 2015
Publication date	Oct 20, 2016
Grant date	—

Abstract

A constant-current controller that supplies a constant current to an inductive load. This controller comprises an electric control circuit module. The electric control circuit module comprises a primary switch and a secondary switch. During a time interval in which the primary switch is closed (t on ), the secondary switch is open and the voltage across the inductive load is equal to the source voltage (V s ). At time t on until the end of a time interval (T), zero volts appears across the inductive load. During this interval, current continues to flow as supplied by the energy stored in the inductance. The periodic current in the inductive load becomes constant with a sufficiently large PWM switching frequency and is dependent upon the parameters of the control circuit and the duration of t on .

First claim

What is claimed is:

1 . A switching circuit wherein said switching circuit provides an average current to an inductive load, wherein said inductive load is an electromagnetic door latch or strike having a coil, said switching circuit having a total circuit resistance and further comprising:
a) a source voltage; b) a first switch connected in series with said coil; c) a second switch connected in parallel with said coil wherein said coil has an inductance; and wherein, from time (t 0 ) to time (t on ) when said first switch is closed and said second switch is open, and source voltage is applied across the coil, a counter EMF decays until the voltage across said coil equals said source voltage at t on ; wherein, from time (t on ) to time (T), when said first switch is open and said second switch is closed, a positive EMF equal to said source voltage is applied across the coil until said positive EMF decays to zero at time (T); and wherein said average current is dependent upon the rate at which said first and second switches are opened and closed with respect to each other.

2 . The switching circuit in accordance with claim 1 wherein said average current is produced by a pulse-width modulated signal.

3 . The switching circuit in accordance with claim 2 wherein said pulse-width modulated signal is modulated to provide a varying periodic current to the inductive load.

4 . A constant-current controller operable to supply a constant current to an inductive load, said controller comprising:
a) a switching circuit comprising:
1) a source voltage;
2) a primary switch;
3) a secondary switch;
wherein, at time (t on ), when said primary switch is closed and said secondary switch is open, a first voltage across said inductive load and a circuit resistance is equal to the source voltage;
wherein, a time interval between time (t on ) and time (T), when said primary switch is open and said secondary switch is closed, current continues to flow to said inductive load as supplied by energy stored in the inductive load,
wherein a periodic current in the inductive load is dependent upon a time duration between time (t 0 ) and time (t on ).

5 . The constant-current controller in accordance with claim 4 , wherein the controller operates as a pulse-width modulation controller to cause the periodic current in the inductive load to become constant through the implementation of a sufficiently large switching rate.

6 . The constant-current controller in accordance with claim 5 , wherein a boundary current and a peak current approach the same constant value as the pulse-width rate increases.

7 . The constant-current controller in accordance with claim 4 , wherein the inductive load is selected from a group consisting of a solenoid, a DC motor and a magnetic actuator.

8 . The constant-current controller in accordance with claim 4 , wherein said switching circuit further comprises:
a current transformer having two primary windings for sensing the current of the inductive load and a secondary winding; wherein said primary windings are connected in series with both said primary switch and said secondary switch; and wherein said secondary winding is connected to a rectifier, said rectifier connected to a burden resistor and a low-pass filter.

9 . The constant-current controller in accordance with claim 8 , wherein said switching circuit further comprises:
4) a timer integrated circuit configured to establish the time interval of the periodic current in the inductive load, wherein said timer integrated circuit receives a signal through an input to initiate the time interval.

10 . The constant-current controller in accordance with claim 4 , wherein said inductive load is configured as having a multiple-filar winding.

11 . The constant-current controller in accordance with claim 4 , wherein said primary switch is a MOSFET and said secondary switch is a free-wheeling diode.

12 . A method of providing a constant-current to an inductive load, the method comprising the steps of:
a) sending an electric current to a switching circuit having a primary switch and a secondary switch; b) sending the electric current through the inductive load and primary switch at time (t 0 ) in which the primary switch is closed and the secondary switch is open, causing the voltage across the inductive load to be substantially equal to a source voltage; c) continuing the electric current through the inductive load and primary switch until time (t on ) during which the primary switch is closed and the secondary switch is open; d) sending the electric current through the inductive load during a time interval between time (t on ) and time (T) during which the secondary switch is closed and the primary switch is open, causing the voltage across the inductive load to equal 0; wherein between time (t on ) and time (T), current continues to flow as supplied by energy stored in the inductive load, wherein a periodic current in the inductive load is dependent upon the duration of time between time (t 0 ) and time (t on ).

13 . The method in accordance with claim 12 further comprising the step of:
e) causing the periodic current in the inductive load to become constant through the implementation of a sufficiently large periodic current frequency generated by a pulse-width modulation controller.

14 . The method in accordance with claim 13 further comprising the step of:
f) causing a boundary current and a peak current to approach the same value as the pulse-width modulated frequency increases.

Assignees

• Hanchett Entry Systems Inc

Inventors

• Davis Brett L
• Shaffer Randall

Classifications

• E05B47/00

  Operating or controlling locks or other fastening devices by electric or magnetic means (electric permutation locks E05B49/00) · CPC title

• H01F7/1615 Primary

  Armatures or stationary parts of magnetic circuit having permanent magnet · CPC title

• E05B2047/0054

  using microprocessor, printed circuits, or the like · CPC title

• E05B47/0012

  with rotary electromotors (actuators with rotary electromotors per se H02K7/06, H02K23/68) · CPC title

• E05B47/02 Primary

  Movement of the bolt by electromagnetic means}; Adaptation of locks, latches, or parts thereof, for movement of the bolt by electromagnetic means {(by means in the striker E05B63/248) · CPC title