BACKGROUND
1. Technical Field
[0001]
The present invention relates to a reverse voltage
regeneration circuit and a dot impact printer.
2. Related Art
[0002]
JP-A-200S-7678 teaches technology that is used in the head
pin drive circuit of a dot impact printer to lower the reverse
voltage produced in a coil that drives a head pin to the voltage
of the power supply that drives the head pins, and return the
reverse voltage to the power supply for reuse.
[0003]
In JP-A-2005-7678, two Zener diodes are connected in series
between the drain and gate, and a resistor is connected between
the gate and source, of an n-channel FET (field effect
transistor) in a regeneration circuit disposed between the coil
that drives the head pin and the power supply for driving the
head pin.
[0004]
When the reverse voltage generated in the head pin drive
coil reaches a level exceeding the sum of the supply voltage
plus the Zener voltage of the two Zener diodes, the n-channel
FET turns on and works to return the reverse voltage produced in
the head pin drive coil to the power supply for driving the head
pin.
[0006]
With the regeneration circuit taught in JP-A-2005-7678, the
n-channel FET is stable while holding an intermediate
resistance, and power based on the reverse voltage produced in
the head pin drive coil is consumed as heat by the n-channel FET
2
operating as a resistor. More specifically, some of the power
derived from the reverse voltage produced in the head pin drive
coil is returned to the power supply for driving the head, and
the rest is spent as heat by the n-channel FET.
[0007]
As a result, the n-channel FET produces heat each time the
head pin is driven, and this heat can lead to thermal runaway or
affect other parts. This makes such measures as using parts with
high heat resistance or providing a heat radiator necessary,
thus increasing cost or device size.
SUMMARY
[0008]
An object of the present invention is to increase the
proportion of power that is recovered to the power supply from
the power generated from the reverse voltage produced in the
head pin drive coil, and reduce heat output from the device.
[0009]
One aspect of the invention is a reverse voltage
regeneration circuit used in a dot impact printer, the reverse
voltage regeneration circuit including a voltage detection
circuit, a control signal generating circuit, a switch circuit,
and a smoothing circuit. The voltage detection circuit changes
the level of a signal output to the control signal generating
circuit according to the amount of reverse voltage produced in a
coil of a head pin drive circuit. The control signal generating
circuit outputs an ON signal to the switch circuit when an
output signal indicating the reverse voltage is greater than or
equal to a specif ic voltage is input from the voltage detection
circuit, and outputs an OFF signal to the switch circuit when an
output signal indicating the reverse voltage is less than the
specific voltage is input from the voltage detection circuit.
3
The switch circuit makes a connection between the coil and the
smoothing circuit when the ON signal is input, and breaks the
connection between the coil and the smoothing circuit when the
OFF signal is input. The smoothing circuit has an output node
connected to the positive potential side of the power supply for
the head pin drive circuit, and smoothes and returns to the
power supply current generated by the reverse voltage supplied
from the coil through the switch circuit.
[0010]
The peak of the reverse voltage can be suppressed and power
consumption by the switch circuit and other components can be
minimized by the switch circuit intermittently supplying current
to the smoothing circuit. Switch devices with a lower rating
(such as FET devices) can therefore be used, and heat output can
be suppressed. A heat radiator is therefore not necessary, or a
small radiator can be used, circuit board size can be minimized,
and device size can be reduced. The size of the power supply can
also be reduced as a result of improved power supply efficiency.
[0011]
In a reverse voltage regeneration circuit according to
another aspect of the invention, the voltage detection circuit
is connected to detect the amount of reverse voltage produced in
the coil of the head pin drive circuit; the control signal
generating circuit is connected to receive input of the output
signal of the voltage detection circuit; and the switch circuit
is disposed between the coil of the head pin drive circuit and
the smoothing circuit, causes the reverse voltage produced in
the coil to drop by making the connection between the coil and
the smoothing circuit, and passing current generated by the
reverse voltage in the coil to the smoothing circuit, when the
ON signal is input from the control signal generating circuit,
and stops the reverse voltage produced in the coil from dropping
4
by breaking the connection between the coil and the smoothing
circuit, and stopping the flow of current generated by the
reverse voltage produced in the coil to the smoothing circuit,
when the reverse voltage goes below the specific voltage due to
the reverse voltage drop causes and the OFF signal from the
control signal generating circuit is input.
[0012]
This configuration enables the switch circuit to reliably
turn on and off repeatedly, and return energy remaining in the
coil to the power supply with low heat output.
[0013]
In another aspect of the invention, the voltage detection
,
circuit changes the level of the output signal by comparing the
reverse voltage with the specific voltage. This configuration
enables rendering the voltage detection circuit easily using a
common part such as a comparator.
[0014]
Further preferably, the voltage detection circuit is a
differential amplifier; and the control signal generating
circuit is included in the differential amplifier. This
configuration enables rendering the voltage detection circuit
easily using an easily obtainable differential amplifier.
[001.5 ]
Further preferably, the control signal generating circuit
inputs the ON signal to the switch circuit after a specific time
passes from when a signal indicating the reverse voltage is
greater than or equal to the specific voltage is output from the
voltage detection circuit, and inputs the OFF signal to the
switch circuit after a specific time passes from when a signal
indicating the reverse voltage is less than the specific voltage
is output from the voltage detection circuit. As a result, the
switch circuit can be reliably turned on and off.
5
[0016]
Further preferably, the switch circuit is a transistor, the
ON signal is a signal that causes the transistor to operate in
the saturation region, and the OFF signal is a signal that
causes the transistor to operate in the cutoff region. This
configuration enables rendering the reverse voltage regeneration
circuit using an easily obtainable transistor.
[0017]
Further preferably, the voltage detection circuit and
control signal generating circuit operate using the positive
potential side of the power supply of the head pin drive circuit
as a reference potential. As a result, power consumption by the
voltage detection circuit and control signal generating circuit
can be suppressed. The reverse voltage regeneration circuit can
also be embodied using low voltage devices, and cost can
therefore be suppressed.
[0018]
Another aspect of the invention is a dot impact printer
having the reverse voltage regeneration circuit described above.
This enables reducing the size of the dot impact printer.
Other objects and attainments together with a fuller
understanding of the invention will become apparent and
appreciated by referring to the following description and claims
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]
FIG. 1 is a circuit diagram showing an example of the
configuration of a head pin driving device that is used in a dot
impact printer according to a preferred embodiment of the
invention.
FIG. 2 conceptually describes an example of the printing
6
operation.
FIG. 3 is used to describe where several voltages or
currents are produced.
FIG. 4 is a timing chart describing the time change in the
voltage or current of selected parts.
FIG. 5 is a circuit diagram showing another exemplary
configuration of the voltage detection circuit 11 and control
signal generating circuit 12.
DESCRIPTION OF EMBODIMENTS
[0020]
A preferred embodiment of the present invention is
described below with reference to the accompanying figures.
[0021]
FIG. 1 is a circuit diagram showing an example of a head
pin driving device used in a dot impact printer according to
this embodiment of the invention. The dot impact printer
according to this embodiment of the invention has a head pin
driving device such as shown in FIG. 1. This head pin driving
device includes a head pin drive circuit 20 and a reverse
voltage regeneration circuit 10.
[0022]
The head pin drive circuit 20 has plural head pins, plural
coils 200, plural switches 201, and plural diodes 202. The head
pin drive circuit 20 according to this embodiment of the
invention has one each of a coil 200, switch 201, and diode 202
for one head pin.
[0023]
The switch 201 is, for example, an n-channel FET with the
gate connected to a microprocessor in the dot impact printer,
the drain connected to the anode of the corresponding diode 202,
and the source connected to ground.
7
[0024]
One end of each coil 200 is connected to the head pin drive
power supply, and the other end is connected to the drain of the
corresponding switch 201.
[0025]
The anode of each diode 202 is connected to the drain of
the corresponding switch 201, and the cathode is connected to
the reverse voltage regeneration circuit 10. The diodes 202 may
be silicon diodes, but are preferably Schottky barrier diodes
with low forward voltage drop.
[0026]
Each switch 201 passes current to the coil 200 when the
print control signal input to the gate thereof from the
microprocessor is HIGH, and drives the head pin with the
magnetic force produced by the current flowing through the coil
200 to strike the paper or other recording medium.
[0027]
When the print control signal input to the gate goes LOW,
the switch 201 cuts off the current flow to the coil 200,
magnetic force is no longer produced in the coil 200, and the
head pin returns to the original position. Reverse voltage is
produced in the coil 200 by this current interruption, and this
reverse voltage is sent through the diode 202 to the reverse
voltage regeneration circuit 10.
[0028]
FIG. 2 schematically describes an example of the printing
operation. When the print control signal output from the
microprocessor in the dot impact printer goes HIGH and the
switch 201 passes current to the coil 200, magnetic force is
produced by the current flowing through the coil 200.
[0029]
As shown in FIG. 2A, this magnetic force causes the metal
8
lever 204 to pivot on the pin 203 and be pulled to the core 206.
The head pin 207 connected to the lever 204 thus strikes the
paper or other recording medium 209 with the ink ribbon 208
therebetween, and forms a dot on the recording medium 209.
[0030]
The return spring 205 then pushes the lever 204 in the
direction away from the core 206, and when the switch 201 stops
the current flow through the coil 200 according to the print
control signal output from the microprocessor, magnetic force is
not produced in the coil 200. As a result, the lever 204 pivots
on the pin 203 due to the urging force of the return spring 205,
and returns to the original position. The head pin 207 therefore
also separates from the ink ribbon 208 and returns to the
original position.
[0031]
Referring again to FIG. I, the reverse voltage regeneration
circuit 10 has a voltage detection circuit II, a control signal
generating circuit 12, a switch circuit 13, and a smoothing
circuit 14.
[0032]
The voltage detection circuit 11 changes the level of the
signal output to the control signal generating circuit 12
according to the amount of reverse voltage produced in the coil
200 of the head pin drive circuit 20.
[0033]
The control signal generating circuit 12 outputs an ON
signal to the switch circuit 13 when an output signal indicating
that the reverse voltage produced in the coil 200 of the head
pin drive circuit 20 equals or exceeds a specific voltage is
input from the voltage detection circuit II, and outputs an OFF
signal to the switch circuit 13 when an output signal indicating
that the reverse voltage went below the specific voltage is
9
input from the voltage detection circuit 11.
[0034]
When an ON signal is input from the control signal
generating circuit 12, the switch circuit 13 makes a connection
between the coil 200 and smoothing circuit 14, and when the OFF
signal is input from the control signal generating circuit 12,
breaks the connection between the coil 200 and smoothing circuit
14.
[0035]
The output of the smoothing circuit 14 is connected through
a diode 15 to the positive potential side of the power supply
for the head pin drive circuit 20, and smoothes and returns
current generated by the reverse voltage supplied from the coil
200 through the switch circuit 13 to the power supply.
[0036]
The voltage detection circuit 11 includes resistor 110,
resistor 111, and Zener diode 112. Resistor 110 and resistor 111
are connected in series with one end connected to the cathode of
the corresponding diode 202, and the other end connected to the
cathode of the Zener diode 112. The anode of the Zener diode 112
is connected to the power supply for driving the head pin.
[0037]
When the reverse voltage produced in the coil 200 and
supplied through the diode 202 exceeds the Zener voltage of the
Zener diode 112, the Zener diode 112 passes current to the
resistors 110 and 111. This causes a voltage drop from the
reverse voltage corresponding to the passing current in resistor
110.
[0038]
As the reverse voltage rises, current flow through the
resistor 110 increases, and the voltage drop of the resistor 110
increases. When the reverse voltage increases, current flow
10
pnp
123,
12 has a
resistor
through the resistor 110 increases, and the voltage drop in the
resistor 110 exceeds a specific voltage (such as 0.7 V) at some
point.
[0039]
The control signal generating circuit
transistor 120, resistor 121, resistor 122,
resistor 124, and npn transistor 125.
[0040]
The base of the pnp transistor 120 is connected to a node
between resistor 110 and resistor 111, the emitter is connected
to the cathode of the diode 202, and the collector is connected
to the head pin drive power supply through the resistors 121 and
122 connected in series.
[0041]
The base of the npn transistor 125 is connected to a node
between resistor 121 and resistor 122, the emitter is connected
to the head pin drive power supply, and the collector is
connected to the cathode of the diode 202 through the resistors
123 and 124 connected in series.
[0042]
When the reverse voltage rises and the voltage drop at the
resistor 110 in the voltage detection circuit 11 exceeds the
specific voltage (such as 0.7 V), the pnp transistor 120 turns
ON and current flows to resistors 121 and 122. As a result, a
voltage drop occurs in resistor 122, exceeds the 0.7 V between
the emitter and base of the npn transistor 125, and the npn
transistor 125 turns ON. Current then flows to resistors 123 and
124, and a voltage drop occurs in resistor 123.
[0043]
When the reverse voltage is high and then starts to drop,
and the voltage drop of the resistor 110 in the voltage
detection circuit 11 goes below the specific voltage, the pnp
11
transistor 120 turns OFF, and current flow to the resistors 121
and 122 is cut off. The voltage drop in the resistor 122
therefore stops, and the npn transistor 125 turns OFF. Current
to the resistors 123 and 124 is thus cut off, and the voltage
drop in resistor 123 goes to zero.
[0044]
Because the resistance of resistors 122 and 123 is
sufficiently high (several ten ohms or more, for example) the
control signal generating circuit 12 operates as a voltage
amplifier that amplifies the voltage from both ends of resistor
110 according to the amount of reverse voltage and outputs the
amplified voltage from both ends of resistor 123.
[0045]
As a result, if the voltage drop in the resistor 110 equals
or exceeds a specific voltage (0.7 V in this embodiment), the
voltage drop at resistor 123 is a voltage (more than 10 V, for
example) sufficient to turn the p-channel FET 130 described
below on in the saturation region (when the ON resistance is
substantially 0 A) .
[0046]
If the voltage drop in the resistor 110 is less than the
specific voltage, the voltage drop of the resistor 123 is a
voltage (such as 0 V) that is sufficient to turn the p-channel
FET 130 described below OFF in the cutoff region (when
substantially no current flows between the drain and source)
[0047]
The voltage detection circuit 11 and control signal
generating circuit 12 operate using the positive potential side
of the head pin drive power supply as the reference potential.
This enables suppressing power consumption by the voltage
detection circuit 11 and control signal generating circuit 12.
12
The cost of the reverse voltage regeneration circuit 10 can also
be reduced because the reverse voltage regeneration circuit 10
can be configured using low voltage devices.
[0048]
The switch circuit 13 has a p-channel FET 130. The gate of
this p-channel FET 130 is connected to a node between resistor
123 and resistor 124, the source is connected to the cathode of
the corresponding diode 202, and the drain is connected to the
smoothing circuit 14.
[0049]
When the npn transistor 125 turns ON and the voltage drop
produced in the resistor 123 by the current flow through the
resistor 123 equals or exceeds a specific voltage (such as
several volts), the p-channel FET 130 receives a signal denoting
this voltage drop as an ON signal, and connects the coil 200 to
the smoothing circuit 14.
[0050]
Because the control signal generating circuit 12 outputs a
sufficiently high voltage (such as ten or more volts) as the ON
signal, the p-channel FET 130 connects the coil 200 to the
smoothing circuit 14 in the saturation region (when the on
resistance is substantially 0 A)
[0051]
When the npn transistor 125 turns OFF and current flow to
the resistor 123 is cut off, causing the voltage drop through
the resistor 123 to go below a specific voltage (several
millivolts, for example), the p-channel FET 130 receives a
signal denoting this voltage drop as an OFF signal, and breaks
the connection between the coil 200 and smoothing circuit 14.
[0052 ]
Because the control signal generating circuit 12 outputs a
13
sufficiently low voltage (such as 0 V) as the OFF signal, the pchannel
FET 130 disconnects the coil 200 from the smoothing
circuit 14 in the cutoff region (when there is substantially no
current flow between the drain and source) .
[0053]
Because the resistance of the p-channel FET 130 is
extremely low when there is continuity between the coil 200 and
smoothing circuit 14, and substantially no current flow to the
p-channel FET 130 when continuity between the coil 200 and
smoothing circuit 14 is interrupted, very little heat is
produced in the p-channel FET 130 by current flow through the pchannel
FET 130.
[0054]
A heat radiator is therefore not needed (or a small
radiator will suffice) for the p-channel FET 130, thereby
helping to minimize the size of the reverse voltage regeneration
circuit 10 and reduce overall device size. In addition, because
the power that is otherwise consumed as heat can be returned to
the power supply, power supply efficiency can be improved and a
smaller power supply can be used.
[0055]
The smoothing circuit 14 includes a diode 140, coil 141,
and capacitor 142. The anode of the diode 140 goes to ground,
and the cathode is connected to the drain of the p-channel FET
130. One end of the coil 141 is connected to the cathode of the
diode 140, and the other end is connected to one end of the
capacitor 142. The other end of the capacitor 142 goes to
ground.
[0056]
The current produced by the reverse voltage supplied from
the coil 200 through the p-channel FET 130 is received by the
smoothing circuit 14 as input to the cathode of the diode 140.
14
smoothes the current received at the
and outputs from a node between the
The smoothing circuit 14
cathode of the diode 140,
coil 141 and capacitor 142.
[0057]
The current that was smoothed by the smoothing circuit 14
is returned to the power supply through the diode 15. Diode 140
and diode 15 may be silicon diodes, but are preferably Schottky
barrier diodes with low forward voltage drop.
[0058]
The change over time in the voltage and current at selected
parts of the reverse voltage regeneration circuit 10 shown in
FIG. 1 is described next.
[0059]
FIG. 3 describes where the several voltages and currents
occur.
[0060]
Veco is the voltage applied to the reverse voltage
regeneration circuit 10 by the reverse voltage produced in the
coil 200, and denotes the voltage at the cathode of the diode
202 referenced to the head pin drive power supply.
[0061]
VR denotes the voltage drop from the reverse voltage
occurring in the resistor 110. Vz denotes the Zener voltage of
the Zener diode 112. Vgs denotes the source voltage of the pchannel
FET 130 referenced to the gate of the p-channel FET 130.
[0062]
Id is the current flowing from the drain of the p-channel
FET 130. Vd is the voltage between the cathode of the diode 140
and ground.
[0063]
FIG. 4 is a timing chart describing the time change in
voltage or current at these selected parts.
15
rises again, the voltage drop VR of the
specific voltage VTh (0.7 V in this
The value of voltage Veco at time t3 is
[0064]
When the print control signal changes from HIGH to LOW at
time tl, the respective switch 201 interrupts the current flow to
the coil 200, and a reverse voltage results in the coil 200.
[0065]
Due to the reverse voltage produced at time tl, the voltage
Veco applied to the reverse voltage regeneration circuit 10 rises
gradually according to the capacitance of the substrate and
lines, and the capacitance of a capacitor that is disposed
between ground and the cathode of the diode 202 to suppress a
sudden rise in voltage Ve=.
[0066]
When voltage Veco reaches the Zener voltage Vz of the Zener
diode 112 at time t2, current flows through the Zener diode 112
and voltage drop VR occurs in resistor 110.
[0067]
When voltage Veco
resistor 110 reaches
embodiment) at time t3.
denoted vol tage Vl.
[0068]
When the voltage drop VR of resistor 110 reaches specific
voltage VTh, the pnp transistor 120 turns ON, current flows to
resistors 121 and 122, and a voltage drop corresponding to the
current results in resistor 122.
[0069]
When the voltage drop of the resistor 122 reaches the
specific voltage (0.7 V in this embodiment) at time t3, the npn
transistor 125 turns ON and current flows to resistors 123 and
124. When the voltage drop of the resistor 123 reaches a
specific voltage (several volts in this embodiment), the pchannel
FET 130 turns ON at time t4.
16
[0070]
Note that the p-channel FET 130 turns ON at time t4 delayed
®t from the time t3 the voltage drop VR of the resistor 110
reaches specific voltage VTh due to delay by the pnp transistor
120 and npn transistor 125 in the control signal generating
circuit 12. This embodiment uses two transistors in the control
signal generating circuit 12, and this delay ®t increases as, the
number of transistor stages increases.
[0071]
When the p-channel FET 130 turns ON at time t4, current Id
based on the reverse voltage in the coil 200 flows through the
p-channel FET 130 to the smoothing circuit 14. As a result,
voltage Veco is applied to the cathode voltage Vd of the diode
140, and voltage Veco begins to drop.
[0072]
When the voltage drop VR of the resistor 110 goes below
specific voltage VTh at time ts, the pnp transistor 120 turns OFF.
As a result, current flow to the resistors 121 and 122 stops,
the voltage drop of the resistor 122 goes to 0, and the npn
transistor 125 turns OFF. When the npn transistor 125 turns OFF,
current flow to the resistors 123 and 124 stops, the voltage
drop of resistor 123 goes to 0, and the p-channel FET 130 turns
OFF at time t6.
[0073]
Note that the p-channel FET 130 turns OFF at time t6 delayed
®t from the time ts the voltage drop VR of the resistor 110 goes
below specific voltage VTh due to delay by the pnp transistor 120
and npn transistor 125 in the control signal generating circuit
12. Note that the delay from time t3 to time t4, and the delay
from time ts to time t6, are denoted by the same reference
numeral ®t in this embodiment, but the delays are not
17
necessarily the same.
[0074]
When the p-channel FET 130 turns OFF at time t6, the reverse
voltage in the coil 200 causes voltage Ve~ to begin rising again.
Note that when the p-channel FET 130 is OFF, the potential of
the node between diode 140 and coil 141 becomes negative,
current flows through the diode 140, there is a forward voltage
drop in the diode 140 from the ground potential, and the cathode
voltage Vd of the diode 140 goes to approximately -1 V.
[0075]
As described above, when the reverse voltage produced in
the coil 200 causes the voltage Veco applied to the reverse
voltage regeneration circuit 10 to rise gradually, the voltage
detection circuit 11 of the reverse voltage regeneration circuit
10 according to this embodiment of the invention detects when
voltage Veco reaches or exceeds a specific voltage, and the
control signal generating circuit 12 outputs to the switch
circuit 13 a signal that turns the switch circuit 13 ON.
[0076]
When switch circuit 13 turns ON, current based on the
reverse voltage in the coil 200 flows through the switch circuit
13 to the smoothing circuit 14, and voltage Veco gradually drops.
When the voltage detection circuit 11 detects that voltage Veco
has gone below the specific voltage, the control signal
generating circuit 12 outputs to the switch circuit 13 a signal
that turns the switch circuit 13 OFF. When the switch circuit 13
turns OFF, voltage Veco stops dropping, and if any energy from the
reverse voltage of the coil 200 remains, voltage Ve~ Starts
rising again.
[0077]
Voltage Veco repeatedly rises and falls, and the p-channel
FET 130 turns ON and OFF, until no more energy can be recovered
18
from the reverse voltage in the coil 200, that is, until the
reverse voltage in the coil 200 cannot increase voltage Veco to
the voltage Vl that produces a voltage drop of specific voltage
VTh in the resistor 110 even when the p-channel FET 130 is OFF.
[0078]
The smoothing circuit 14 smoothes the current that is
supplied intermittently by the p-channel FET 130, and returns
the current to the head pin drive power supply through the diode
15 provided to prevent current backflow.
[0079 ]
The upper limit Vu of the range through which voltage Veco
rises and falls is determined by the voltage resistance of the
parts rendering the reverse voltage regeneration circuit 10. The
average voltage of the voltage Ve= that rises and falls is
determined by the configuration of the smoothing circuit that
produces a power supply of a particular voltage.
[0080]
For example, if a 42-V head pin drive power supply is used
and the smoothing circuit 14 is configured as shown in FIG. I,
current smoothing is based on a voltage supplied at an
approximately 50% duty, and voltage goes to substantially 0 V
when off, a voltage of approximately 100 V is required when on
considering current consumption by the smoothing circuit.
[0081]
In practice, a design in which the average voltage during
the period when the p-channel FET 130 is ON is approximately 100
V is preferable because a dropped voltage Veco is supplied to the
smoothing circuit 14 during the period from time t4 to time t6
when the p-channel FET 130 is ON.
[0082]
When printing is stopped by cutting off current to the coil
200, reverse voltage occurs in the coil 200, and if the current
19
produced by this reverse voltage is released slowly over time,
current will continue flowing through the coil 200 at the same
time. As a result, magnetic force is produced in the coil 200
and interferes with the operation that returns the head pin to
the original position after printing, and the head pin may catch
the ink ribbon or paper or other recording medium.
[0083]
The head pin must therefore be returned quickly to the
original position after printing in order to achieve high speed
printing. Cons idering the speed of the printhead and the paper
feed rate, this embodiment is designed to deplete the current
produced by the reverse vol tage in the coi1 200 wi thin several
ten microseconds after printing.
[0084]
The lower limit VL of the range in which voltage Veco rises
and falls is preferably set as high as possible in order to
quickly deplete the current produced by the reverse voltage in
the coil 200. However, as described above, the upper limit Vu of
the voltage Veco range and the average voltage Veco cannot be
changed because of such limitations as the voltage resistance of
component parts and the configuration of the smoothing circuit
that produces a power supply of the desired voltage.
[0085]
Voltage Veco can conceivably be made to vary within a narrow
range by rapidly switching the p-channel FET 130 around the
designed average voltage, but the upper limit of the p- channel
FET 130 operating frequency is approximately several megahertz,
and the p-channel FET 130 cannot be switched more rapidly.
[0086]
Therefore, in order to set the
possible while observing specific
voltage resistance of component parts
20
lower limit VL as high as
limitations such as the
and the configuration of
the smoothing circuit that produces a power supply of the
desired voltage, the lower limit VL of the range of the rise and
fall of voltage Veco is determined by the maximum frequency at
which the p-channel FET 130 can be switched.
[0087]
A preferred embodiment of the invention is described above.
,[0088]
As will be understood from the foregoing description, a dot
impact printer according to this embodiment of the invention can
increase the proportion of power that is recovered to the power
supply from the power generated by the reverse voltage produced
in the head pin drive coil 200, and can reduce heat output by
component devices.
[0089]
The invention is not limited to the foregoing embodiment,
and can be varied in many ways. For example, the voltage
detection circuit 11 in the above embodiment includes resistors
and a Zener diode, but the invention is not so limited.
[0090]
For example, a comparator or other device that changes the
level of the signal output to the control signal generating
circuit 12 by comparing the voltage Veco that is applied to the
reverse voltage regeneration circuit 10 according to the reverse
voltage in the coil 200 with a predetermined voltage could be
used.
Further alternatively, the voltage detection circuit 11 and
control signal generating circuit 12 could include a
differential amplifier.
[0091]
The voltage detection circuit 11 and control signal
generating circuit 12 in the embodiment described above are also
not limited to the configurations shown in FIG. 1, and could be
21
configured as shown in FIG. 5, for example.
[0092]
FIG. 5 is a circuit diagram showing other configurations of
the voltage detection circuit 11 and control signal generating
circuit 12. In this embodiment the voltage detection circuit 11
includes a Zener diode 300 and resistor 301. The cathode of the
Zener diode 300 is connected to the cathode of diode 202, and
the anode of the Zener diode 300 is connected through the
resistor 301 to the head pin drive power supply.
[0093]
The control signal generating circuit 12 includes a
resistor 302, resistor 303, and n-channel FET 304. The resistor
302 and resistor 303 are connected in series with one end
connected to the cathode of the diode 202, and the other end
connected to the drain of the n-channel FET 304. The gate of the
n-channel FET 304 is connected to the anode of the Zener diode
300, and the source is connected to the head pin drive power
supply.
[0094]
When the voltage Veco applied to the cathode of the Zener
diode 300 and based on the reverse vol tage of the coi1 200
exceeds the Zener voltage of the Zener diode 300, current flows
through the Zener diode 300 and resistor 301, and the n-channel
FET 304 turns ON when the voltage drop of the resistor 301
reaches a specific value.
[0095]
When the n-channel FET 304 turns ON, current flows to
resistors 302 and 303, and the p-channel FET 130 turns ON when
the voltage drop of resistor 302 reaches a specific value. If
the voltage drop in the resistor 302 is a voltage drop
sufficient to turn the p-channel FET 130 ON in the saturation
region by turning the n-channel FET 304 ON, this configuration
22
can also turn the p-channel FET 130 ON in the saturation region
and OFF in the cutoff region.
[0096]
Because this configuration uses one transistor stage in the
control signal generating circuit 12, the delay ®t described in
FIG. 4 is shorter than with the control signal generating
circuit 12 configuration shown in FIG. 1. If delay ®t is short,
faster switching is possible within the range of the frequency
characteristic of the p-channel FET 130.
[0097]
Further alternatively, the switch circuit 13 shown in FIG.
1 could include a charge pump and an n-channel FET device, for
example.
[0098]
The invention being thus described, it will be obvious that
it may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the
invention, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope
of the following claims.
23

WE CLAIM:
1. A reverse voltage regeneration circuit used in a dot impact
printer, comprising:
a voltage detection circuit;
a control signal generating circuit;
a switch circuit; and
a smoothing circuit;
wherein the voltage detection circuit changes the level of
a signal output to the control signal generating circuit
according to the amount of reverse voltage produced in a coil of
a head pin drive circuit;
the control signal generating circuit outputs an ON signal
to the switch circuit when an output signal indicating the
reverse voltage is greater than or equal to a specific voltage
is input from the voltage detection circuit, and
outputs an OFF signal to the switch circuit when an
output signal indicating the reverse voltage is less than the
specific voltage is input from the voltage detection circuit;
the switch circuit makes a connection between the coil and
the smoothing circuit when the ON signal is input, and
breaks the connection between the coil and the
smoothing circuit when the OFF signal is input; and
the smoothing circuit has an output node connected to the
positive side of the power supply for the head pin drive
circuit, and smoothes and returns to the power supply current
generated by the reverse voltage supplied from the coil through
the switch circuit.
2. The reverse voltage regeneration circuit as claimed in
claim I, wherein:
the voltage detection circuit is connected to detect the
amount of reverse voltage produced in the coil of the head pin
24
drive circuit;
the control signal generating circuit is connected to
receive input of the output signal of the voltage detection
circuit; and
the switch circuit is disposed between the coil of the head
pin drive circuit and the smoothing circuit,
causes the reverse voltage produced in the coil to
drop by making the connection between the coil and the smoothing
circuit, and passing current generated by the reverse voltage in
the coil to the smoothing circuit, when the ON signal is input
from the control signal generating circuit, and
stops the reverse voltage produced in the coil from
dropping by breaking the connection between the coil and the
smoothing circuit, and stopping the flow of current generated by
the reverse voltage produced in the coil to the smoothing
circuit, when the reverse voltage goes below the specific
voltage due to the reverse voltage drop causes and the OFF
signal from the control signal generating circuit is input.
3. The reverse voltage regeneration circuit as claimed in
claim 1, wherein:
the voltage detection circuit changes the level of the
output signal by comparing the reverse voltage with the specific
voltage.
4. The reverse voltage regeneration circuit as claimed in
claim 3, wherein:
the voltage detection circuit is a differential amplifier;
and
the control signal generating circuit is included in the
differential amplifier.
25
5. The reverse voltage regeneration circuit as claimed in
claim 3 or 4, wherein:
the control signal generating circuit inputs the ON signal
to the switch circuit after a specific time passes from when a
signal indicating the reverse voltage is greater than or equal
to the specific voltage is output from the voltage detection
circuit, and
inputs the OFF signal to the switch circuit after a
specific time passes from when a signal indicating the reverse
voltage is less than the specific voltage is output from the
voltage detection circuit.
6. The reverse voltage regeneration circuit as claimed in any
of claims 1 to 5, wherein:
the switch circuit is a transistor;
the ON signal is a signal that causes the transistor to
operate in the saturation region; and
the OFF signal is a signal that causes the transistor to
operate in the cutoff region.
7. The reverse voltage regeneration circuit as claimed in any
of claims 1 to 6, wherein:
the voltage detection circuit and control signal generating
circuit operate using the positive potential side of the power
supply of the head pin drive circuit as a reference potential.
8. A dot impact printer comprising the reverse voltage
regeneration circuit as claimed in any of claims 1 to 7.