US 4,227,230 A · Switch mode driver

Abstract

A switch mode driver for a wire matrix printer employs a single power switch circuit to connect one or more solenoids across a DC source or power and to disconnect those solenoids from that source. Enable signals are provided to select any one or all of the solenoids, such enable signals remaining for a predetermined time during which a slewing period, followed by a chopping period, occur and after which energy remaining in the selected solenoids is returned to the DC power source. The initial ramping of current through the selected solenoids occurs when the power switch circuit is closed for a time period determined by an RC circuit, such time period defining the slewing period. Then the power switch opens and the chopping period begins. The charge on the capacitor of the RC circuit is discharged and at a certain voltage point, the power switch is again closed until the charge on the capacitor of the RC circuit again reaches a predetermined voltage at which time the power switch opens. This chopping action continues until the enabling signals are disabled. In this preferred embodiment, the time when the power switch is turned on is approximately 1/10 of the chopping period.

Claims12

Dependent claims

A wire matrix switch mode driver for connection to a DC source of power for driving the armatures of a plurality of solenoids that are selectively connected across and disconnected from the DC source, including means for providing enable signals for a predetermined time for selecting each solenoid, comprising:

(a) enabling means connected to the plurality of solenoids and operatively connected to receive the enable signals and responsive thereto to provide a current path for each of the selected solenoids both when the plurality of solenoids is connected across the DC source and when it is disconnected from the DC source;
(b) a power switch adapted to drive any or all of the plurality of solenoids, connected to the DC source of power and to the plurality of solenoids, and having control means for permitting the power switch to close, thereby connecting the plurality of solenoids to the DC source and for permitting the power switch to open, thereby disconnecting the plurality of solenoids from the DC source;
and
(c) timing means responsive to the means for providing enable signals and connected to the control means to permit the power switch to open after it has been closed a predetermined time, and to close after it has been open a predetermined time.

1 more element

(a) enabling means connected to the plurality of solenoids and operatively connected to receive the enable signals and responsive thereto to provide a current path for each of the selected solenoids both when the plurality of solenoids is connected across the DC source and when it is disconnected from the DC source;
(b) a power transistor connected to the DC source of power and to the plurality of solenoids, and having control means for enabling the power transistor, thereby connecting the plurality of solenoids to the DC source and for disabling the power transistor, thereby disconnecting the plurality of solenoids from the DC source;
and
(c) timing means responsive to the means for providing enable signals and connected to the control means to disable the power transistor after it has been enabled a predetermined time, and to enable it after it has been disabled a predetermined time wherein the timing means comprises:
(i) an RC circuit, connected to the enabling means;
and
(ii) comparator means having a first input connected to the enabling means for establishing a reference voltage, and a second input connected to the RC circuit for providing an output signal to disable the power transistor when the first and second input voltages reach a prescribed difference in magnitude.

4 more elements

Dependencies are inferred from the claim text.

Switch mode driver

Life of this patent

Switch mode driver

Life of this patent

Abstract

Claims12