GB2247998A

GB2247998A - Motor control circuit for head lamp cleaner system

Info

Publication number: GB2247998A
Application number: GB9119263A
Authority: GB
Inventors: Hiroki Shibata; Hitoshi Takeda
Original assignee: Koito Manufacturing Co Ltd
Current assignee: Koito Manufacturing Co Ltd
Priority date: 1990-09-11
Filing date: 1991-09-09
Publication date: 1992-03-18
Anticipated expiration: 2011-09-09
Also published as: GB9119263D0; DE4130200A1; DE4130200C2; JPH04121256A; GB2247998B; JP2573885B2

Abstract

A head lamp cleaner control circuit which is substantially resistive against corrosion duo to moisture and humidity, durable against vibration, is scarcely affected by magnetic fields, and can be combined with the cleaner motor with a simple water-proof structure, employs a semiconductor switching device eg an N-channel MOSFET (TFET) having a source electrode S connected to one terminal of a cleaner motor 3 the other terminal of which is grounded. Alternatively a bipolar transistor may be employed. A drain electrode D is connected to the positive terminal of a power source 9 mounted on a vehicle. A capacitor C6 and diode D4 are connected between the source electrode of the MOSFET and the positive terminal of the power source through an ignition switch 8, so that the capacitor is charged in response to the ignition switch being on. A timer circuit 10-2 starts a timing operation when a cleaner switch 1 is turned on with the ignition switch turned on, to raise the potential level of the gate electrode G of the MOSFET above that of the source electrode, in order to render the MOSFET conductive, and applies the charge voltage of the capacitor to the gate electrode for a predetermined period of time. <IMAGE>

Description

1 M.A CLEANER CONTROL DEVICE The present invention relates to a control

circuit for a headlamp cleaner which jets a cleaning solution contained in a cleaner tank through a nozzle to wash the headlamp.

Some recent vehicles have been provided with headlamp cleaners to clean their headlamps. Fig. 9 shows the arrangement of a conventional headlamp cleaner. With the ignition switch turned on, a cleaner switch 1 is turned on, whereby a cleaner motor 3 is driven through a control unit 2. As a result, the cleaning solution f rom a cleaner tank 4 is jetted from a nozzle 5 to clean a headlamp 6, as depicted in Fig. 10.

Fig. 11 shows a headlamp cleaner control circuit in the control unit 2. The headlamp cleaner control circuit includes PNP transistors Q1 and Q2, an NPN transistor Q3, diodes D1 through DS, a relay RY with a normally open contact xy, capacitors Cl and C2, and resistors Rl through R7. In Fig. 11, reference numeral 8 designates an ignition switch, and 9, a power soiii:ce mounted on the vehicle.

The operation of the control circuit thus constructed will be described.

When the cleaner switch 1 is in the "off,' state with the ignition switch 8 turned on, current flows from the positive terminal of the power source 9 through the ignition switch 8, is the resistor R7, the resistor R6, the capacitor C2. the diode D5, the capacitor 1 (the resistor R4), and the diode D1 to ground, in the stated order, so that the capacitor C2 is charged. At the same time, current flows from the positive terminal of the power source 9 through the ignition switch 8, the resistor R51 the diode DS, the base-emitter junction of the transistor Q3, and the diode D1 to ground, so that the transistor Q3 is rendered conductive (on). With the transistor Q3 turned on in this manner, the transistor Q2 is turned on, as a result of which the potential at the connecting point of the base of the transistor Q1 and the collector of the transistor Q2 becomes equal to the supply voltage E (for instance +12 volts). Therefore, the transistor Q1 is maintained nonconductive (off), and accordingly no current flows in the coil CL of the relay RY, and the normally open contact xy is held opened. Hence, no current is supplied from the power source 9 to the cleaner motor 3; that is, the motor 3 is not operated.

When, on the other hand, the cleaner switch 1 is turned on with the ignition switch 8 turned on, the potential at the connecting point of the capacitor C2 a-. zj,,a j.-jist:6r R5 falls quickly as the capacitor C2 is discharged. Since the potential at the connecting point B falls quickly in this manner, the transistor Q3 is rendered non-conductive (off) as it is then reverse-biased, so that the transistor Q2 is also rendered nonconductive (off). Accordingly, the potential at the connecting f a point A becomes ground level, so that the transistor Q1 is rendered conductive (on). As a result, current flows in the coil CL of the relay RY, and the normally open contact x-y is therefore closed, so that current is supplied from the power source 9 to the cleaner motor 3. That is, the cleaner motor 3 is operated to jet the cleaning solution.

on the other hand, as the capacitor C2 is discharged, the potential at the connecting point B is increased gradually. When the potential reaches a certain value, that is, when a predetermined time has passed, the transistor Q3 is turned on. Accordingly, the transistor Q2 is turned on, and therefore the transistor Q1 is turned off. As a result, the application of current to the coil CL of the relay RY is suspended, so that the normally open contact xy is opened, and the cleaner motor 3 is therefore stopped.

The headlamp cleaner control circuit is mounted as a printed base assembly 2-1 on a printed wiring board 2-11, on which its circuit elements have been mounted. The printed base assembly 2-1 is accommodated in a casing 2-2, thus forming the control unit 2. Fli.!3 shows the printed base assembly 2-1 accommodated in the casing. The printed base assembly 2-1 is mounted on peening legs 2-21 and 2-22 of the casing 2-2 by peening them at room temperature. The casing 2-2 is closed through an O-ring 2-3 with a cover 2-4 with the printed base assembly held therein, and the cover 2-4 is secured to the is casing 2-2 with tapping screws 2-5. Hence, the control unit thus formed is waterproof.

However, in the above-described conventional headlamp cleaner control circuit, the cleaner motor 3 is connected to the positive terminal of the power source 9 on the vehicle at all times. That is, since the contact capacity of the ignition switch 8 is small, the supply voltage +12 volts is applied to the cleaner motor 3 at all times. Therefore, electrochemical corrosion is liable to occur due, for instance, to moisture or humidity.

In order to overcome this difficulty, the present applicant has proposed a headlamp cleaner control circuit and disclosed the same in Japanese Utility Patent Application No. 4735411990. In this control circuit, one terminal of the cleaner motor is grounded, and the normally open contacts of a relay are connected between the other terminal of the cleaner motor and the positive terminal of a power source on the vehicle. When a cleaner switch is turned on with the ignition switch turned on, the relay is driven so that its normally open contacts are closed for a predett.,.. ll.'-;- -' period of time.

However, the employment of the relay by the headlamp cleaner control circuit gives rise to the following difficulties. and makes it difficult to combine the circuit with the cleaner motor:

(1) The normally open contacts are liable to be is electrically corroded, for instance, by moisture or humidity. Thus, the required waterproof structure is rather intricate.

(2) The control circuit is liable to be damaged and rendered inoperative by vibration.

(3) The control circuit is liable to be affected by magnetic fields.

The foregoing and other problems have been overcome with the invention by the provision of a headlamp cleaner control circuit which, according to the invention, comprises: an Nchannel MOSFET having a source electrode connected to one terminal of a cleaner motor the other terminal of which is grounded, and a drain electrode connected to the positive terminal of a power source mounted on a vehicle; charging means connected between the source electrode of the MOSFET and the positive terminal of the power source through an ignition switch, the charging means being charged in response to the "on" operation of the ignition switch; and timer means which starts a timer operation when a cleaner switch is turned on with the ignition switch rux:i,ed on, to raise the level of the gate electrode of the MOSFET to render the MOSFET conductive. and which applies a charge voltage of the charging means to the gate electrode for a predetermined period of time lasting until the timer operation is ended, to maintain the level of the gate electrode higher than that of the source electrode.

is In the headlamp cleaner control circuit of the invention, one terminal of the cleaner motor is grounded, and the other terminal is connected to the positive terminal of the power source through the source electrode and the drain electrode of the N-channel MOSFET.

Furthermore, because of the employment of the N-channel MOSFET, the control circuit is substantially resistive to corrosion attributed to moisture, humidity, etc. In addition, for the same reason, it is durable against vibration, and is scarcely affected by magnetic fields. Thus, the inventive control circuit can be combined with the cleaner motor with ease.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs. 1 through 6 are circuit diagrams showing the arrangements of respective f irst through sixth examples of a headlamp cleaner control circuit according to the invention; Fig. 7 is a waveform diagram for a description of the operation of the headlamp cleaner control circuit shown in Fig. 1;

Fig. 8 is a sect-ionci -11d- -si-.Lew showing an example of a structure formed by combining the headlamp cleaner control circuit with a cleaner motor; Fig. 9 is an explanatory diagram outlining the arrangement of a headlamp cleaner mounted on a vihicle; Fig. 10 is a perspective view for a description of the operation of the headlamp cleaner shown in Fig. 9; Fig. 11 is a circuit diagram showing a conventional headlamp cleaner control circuit; Fig. 12 is a perspective view showing a printed base assembly including the conventional headlamp cleaner control circuit and a casing for accommodating the printed base assembly; and Fig. 13 is a sectional side view showing the printed base assembly accommodated in the casing.

A headlamp cleaner control circuit constructed according to the invention will now be described in detail.

Fig. 1 is a circuit diagram showing the arrangement of a first example of a headlamp cleaner control circuit according to the invention. In Fig. 1, parts corresponding functionally to those which have been already described with reference to Fig. 11 are therefore designated by the same reference numerals or characters.

The headlamp cleaner control circuit 101 includes an interface section 101, a time..I,-tion 10-2, a power-on reset section 10-3, and a drive section 10-4. The interface section 10-1 is composed of capacitors Cl and C2, a diode D1, an NPN transistor Trl, and resistors R1 through R4. The timer section includes capacitors C3 and C4, a diode D2. an NPN transistor Tr2, a PNP transistor Tr3, and resistors R5 through R8. The power-on reset section 10-3 is f ormed by a capacitor C5, a diode D3, an NPN transistor Tr4, and resistors R9 and R10. The drive section 10-4 is made up of a capacitor C6, a diode D4. an N-channel MOSFET Tm, and resistor Rll and R12.

In the drive section 10-4, the source electrode S of the MOSFET Tm is connected to one terminal of the cleaner motor 3, the other terminal of which is grounded, and the positive terminal of the power source 9 installed on the vehicle is connected to the drain electrode D of the MOSFET TyET. A series circuit of the diode D4 and the capacitor C6 is connected through the ignition switch 8 between the positive terminal of the power source 9 and the source electrode S of the MOSFET Tm. The gate electrode G of the MOSFET TyET is grounded through the resistors R12 and Rll. In the timer section 10-2, the emitter of the transistor Tr3 is connected to the connecting point E of the diode D4 and the capacitor C6 in the drive section 10-4. The collector of the transistor Tr3 is connected to the connecting points of the resistors R12 and R11. The base of the transistor Tr3 is connected to the connecting point of ---i-ie te=inal of the resistor R7 and one terminal of the resistor RS. The other terminal of the resistor R7 is connected to the emitter of the transistor Tr3. The other terminal of the resistor R8 is grounded through a capacitor C4.

The operation of the headlamp cleaner control circuit 101 is thus constructed will now be described in detail.

When the cleaner switch 1 is in the "off,' state with the ignition switch 8 turned on, current f lows f rom the power source 9 through the ignition switch 8. the diode D4, and the capacitor C6 to the cleaner motor 3, so that the capacitor C6 is charged. The potential at the source electrode S of the MOSPET TnT is abruptly raised to +12 volts (at the time instant t, in waveform (c) in Fig. 7) and quickly decreased to ground level. In this case, the potential at the gate electrode G of the MOSFET TyET is lower than the potential at the source electrode S, being at ground level. Therefore, the MOSFET Tm is maintained non-conductive (off), so that no current is supplied from the power source 9 to the cleaner motor 3; that is, the motor 3 is maintained at rest.

When the cleaner switch 1 is in the "off" state with the ignition switch 8 turned on as described above, current flows from the power source 9 through the ignition switch 8, the resistor R1, and the resistor R2 to the capacitor C2 (the resistor R3), so that the transistor Trl is maintained conductive (on). At the same time, cuircyit flows from the power source 9 through the ignition switch 8, the diode D4, the resistor R7, and the resistor R8 to the capacitor C4, so that the capacitor C4 is charged. In addition, current flows from the power source 9 through the ignition switch 8, the capacitor CS, and the resistor R9 to the resistor R10, so that the 9 - capacitor C5 is charged. In the control circuit shown in Fig. 1j, the time constant of the charge curve for the capacitor C5 is larger than that of the charge curve for the capacitor C4. Hence, even if the transistor Tr3 is rendered conductive (on) while the capacitor C4 is being charged, the transistor Tr4 is maintained conductive (on), so that the potential at the gate electrode G is held at ground level. Accordingly, the MOSFET Tm is maintained rendered non-conductive (off), and therefore no erroneous operation is caused.

When, on the other hand, the cleaner switch 1 is turned on with the ignition switch 8 held turned off, the transistor Tri is rendered non-conductive (of f) f or a very short period of time (one-shot time), so that the transistor Tr2 is rendered conductive (on). As a result, the capacitor C4 is discharged through the resistor R6 and the transistor Tr2, so that the base potential is decreased, and accordingly the transistor Tr3 is rendered conductive (at the time instant t2 in wavef orm (a) in Fig. 7); that is, the timer operation of the timer section 10-2 is started. As a result, current flows from the power source 9 thro ignition switch 8, the diode D4, and the transistor Tr3 to the resistor Rll. Hence, the potential (+12 volts) at the connecting point E of the diode D4 and the capacitor C6 is applied to the gate electrode G of the MOSFET Tp= (at the time instant t2 in wavef orm (b) in Fig - 7), so that the potential at the gate electrode G becomes higher than that - is at the source electrode S, thus rendering the MOSFET TIPET conductive (on). That is. the potential at the source electrode S is raised to +12 volts (at the time instant t2 in waveform (d) in Fig. 7), so that current is supplied to the cleaner motor 3, whereby the cleaning solution jetting operation is started.

on the other hand.. when the potential at the source electrode S of the MOSFET TyET is raised to +12 volts. the potential of the connecting point E is abruptly increased to +24 volts (at the time instant t2 in waveform (d) in Fig. 7).

As the capacitor C6 is discharged through the transistor Tr3, the potential at the connecting point E is gradually decreased, and accordingly the potential at the gate electrode G is also gradually decreased. When the transistor Tr2 is rendered non conductive during this period of time, the capacitor C4 is charged. As a result, the base potential of the transistor Tr3 is gradually increased, and finally the transistor Tr3 is rendered non-conductive (at the time instant t3 in waveform (a) in Fig. 7). That is, the timer operation of the timer section 10-2 is ended, and the potential of the cle-trode G is forcibly set to ground level (at the time instant t3 in waveform (b) in Fig. 7). As a result. the MOSFET TyET is turned off, so that the potential of the source electrode S is set to ground level (at the time instant t3 in waveform (c) in Fig.

7), and the potential of the connecting point E is decreased to is +12 volts (at the time instant t3 in waveform (c) in Fig. 7).

That is, for the time T marked by the timer for which the transistor Tr3 is kept conductive (on), i.e., for the time T which lasts until the end of the timer operation of the timer section 10-2, the charge voltage of the capacitor C6 is applied to the gate electrode, so that the potential of the gate electrode G is higher than that of the source electrode S. Thus, for this period of time, the current is supplied to the cleaner motor 3, so that the jetting of the cleaning solution is continued. After the time T, the MOSFET TyET is turned off, so that the application of current to the cleaner motor 3 is suspended; that is, the cleaner motor 3 is stopped.

Fig. 2 shows a second example of a headlamp cleaner control circuit according to the invention. In the headlamp cleaner control circuit 102. the timer section 10-21 employs a comparator 1C2. The power-on reset section 10-31 is composed of a diode D3, a capacitor CS, and resistors R8 and R9. The potential at the connecting point of the capacitor CS and the resistor R9 is applied to the inverting input terminal of the co,,, iarator iC2. to the non-inverting input terminal of which the potential at the connecting point of a capacitor C4 and a resistor R7 is applied. The output of the comparator IC2 is applied through a resistor R11 to the base of a transistor Tr3, which is provided on the side of the drive section 10-41.

When, in the headlamp cleaner control circuit 102. the 1 cleaner switch 1 is turned on with the ignition switch held turned on, the transistor Tr2 is rendered conductive (on), so that the capacitor C4 is discharged. and accordingly the voltage applied to the non-inverting input terminal of the comparator IC2 is decreased, and the output of the comparator IC2 is set to the "L" level. As a result, the transistor Tr3 is turned on, so that the voltage (+12 volts) at the connecting point E is applied to the gate electrode G of the MOSPET TyET, and the latter is turned on. In this case, owing to the charge voltage of the capacitor C6, the potential of the gate electrode G is held higher than that of the source electrode S. When the transistor Tr2 is turned off during this period, the capacitor C4 is charged again, so that the voltage applied to the non-inverting input terminal (+) of the comparator IC2 is is gradually increased. When the voltage applied to the non- inverting input terminal becomes higher than that applied to the inverting input terminal, the output of the comparator IC2 is raised to the "H" level, and the transistor Tr3 is turned off, so that the potential of the gate electrode G of the MOSFET Tm is forcibly set to ground level. In responsc zo the setting the potential of the gate electrode G to ground level, the MOSFET TyET is turned off, and the potential of the source electrode S is set to ground level again.

In the headlamp cleaner control circuit 102. the time constant of the charge curve for the capacitor C5 is larger - 13 c is than that of the charge curve for the capacitor C4. Therefore, when the ignition switch 8 is turned on, voltage is applied to the inverting input terminal of the comparator IC2 later than to the non-inverting input terminal. Hence, the voltage applied to the inverting input terminal will never be higher than that applied to the non-inverting input terminal. This feature prevents the erroneous operation of the control circuit. Furthermore in the headlamp cleaner control circuit 102r the time constant of the discharge curve of the capacitor C5 is smaller than that of the discharge curve of the capacitor C4. Therefore, when the ignition switch 8 is turned off, the voltage set for the inverting input terminal of the comparator IC2 is eliminated earlier than that set for the non-inverting input terminal. Hence, the voltage applied to the inverting input terminal will never become higher than that applied to the non-inverting input terminal. This characteristic prevents erroneous operation of the control circuit.

Fig. 3 shows a third example of a heeadlamp cleaner control circuit according to the invention. The headlamp cleaner C.L-rCUIt 103 shown in Fig. 3 dif f ers from the above described headlamp cleaner control circuit 102 in the connection of the inverting input terminal and the non inverting input terminal of the timer section 10-211 and the arrangement of the drive section 10-42. That is, in the drive section 10-42, the transistor Tr3 and its related circuits are is eliminated, and the connecting point of the diode D4 and the capacitor C6 is connected through the resistor R10 to the output of the comparator IC2. When, in the headlamp cleaner control circuit 103 thus constructed, the cleaner switch 1 is turned on with the ignition switch 8 turned on, the output of the comparator IC2 is raised to the "H" level. As a result, an "H" level voltage is applied to the gate electrode G of the MOSFET Tyrr, so that the latter Tyr:,T is turned on. When the MOSFET TyET is rendered conductive (on) in this mannar, and the potential of the source electrode S is raised to +12 volts, the potential of the connecting point E is raised to +24 volts quickly. As a result, the potential of the gate electrode G of the MOSFET TyET is also increased quickly, thus being maintained higher than that of the source electrode S. Therefore, the MOSFET TlET is maintained rendered conductive. In this operation. the capacitor C6 is scarcely discharged. That is, the capacitor C6 is slightly discharged because of leakage of current; however, the capacitor C6 is held substantially charged. In addition to the charge voltage of the capacitor C6, the high potential of the gate electrode maintainz, MOSFET TyET conductive. The employment of the above-described technique permits the use of a capacitor C6 which is small in capacitance, aiding in a reduction of the manufacturing cost.

Fig. 4 shows a fourth example of the headlamp cleaner control circuit according to the invention. The headlamp is 2.

cleaner control circuit 104 shown in Fig. 4 differs from the abovedescribed headlamp cleaner control Circuit 103 in the arrangement of the interface section. That is. in the interface section 10-11, a comparator IC1 is employed instead of the transistor Trl (Fig. 3). In the headlamp cleaner control circuit, an IC package may be effectively used. That is, two operational amplifiers (operational amplifiers are commonly packaged in pairs) may be employed as the comparators IC1 and IC2.

Fig. 5 shows a fifth example of a headlamp cleaner control circuit according to the invention. The headlamp cleaner control circuit 105 shown in Fig. 5 is the same as the abovedescribed headlamp cleaner control circuit 103 except for the interface section 10-12. That is, in the interface section 10-12, a PNP transistor is employed as.the transistor Trl. The employment of the PNP transistor prevents the occurrence of erroneous operation when the ignition switch 8 is turned off. This will be described in more detail.

In the case of the headlamp cleaner control Circuit 103r wh= the ignition switch 8 is turned off, the capacitors C4 and C5 are discharged,, so that the transistor Tr2 is rendered conductive (on). As a result, the output of the comparator IC2 is raised to the "H" level,, and the MOSFET TFET is turned on. Therefore, current is supplied to the cleaner motor 3 for a short period of time. On the other hand, in the case of the headlamp cleaner control circuit 105, when the ignition switch 8 is turned, the transistor Tr2 is not rendered conductive (on) because the transistor Trl is maintained non-conductive (off), as a result of which the supply of current to the cleaner motor 3 is suspended.

Fig. 6 shows a sixth example of a headlamp cleaner control circuit according to the invention. The headlamp cleaner control Circuit 106 has the same general arrangement as the above-described headlamp cleaner control circuit 10.5 except for its timer section 10-22. That is, in the timer section 10-22. a comparator IC1 is employed instead of the transistor Tr2.

As described above, in the headlamp cleaner control circuit 10 according to the invention, one terminal of the cleaner motor 3 is grounded at all times, and the other terminal is connected to the positive terminal of the power supply 9 through the source electrode S and the drain electrode D of the N-channel MOSFET TYET at all times. Therefore, the control circuit is substantially free from the difficulty of corrosion, for instance, by moisture or humidity. The Nchannel MOSFET TyET is substantially resistive against corrosion due to moisture, humidity, etc., durable against vibration, and is scarcely affected by magnetic fields. In addition, it is low in non,' resistance, and produces only a small quantity of heat. Thereforer the headlamp cleaner control circuit and the cleaner motor 3 can be constructed as one unit with a simple g.i is waterproof structure.

Fig. 8 is a sectional side view of the headlamp cleaner control circuit 10 and the cleaner motor 3 constructed as a single unit. In Fig. 8, reference numeral 3-1 designates the armature; 3-2, the stator; 3-31 and 3-32. bearings; 3-4, the commutator; and 3-5, a motor casing. In this unit, the headlamp cleaner control circuit 10 is mounted on a printed circuit board 11 to form a print base assembly 12. The print base assembly 12 is arranged on the bottom of the motor casing 3-5 with a simple waterproof structure. A male connector 14 is connected to a female connector 13 to supply current to the headlamp cleaner control circuit 10.

In the headlamp cleaner control circuit 10, a P-channel MOSFET may be employed instead of the N-channel MOSFET described above. However, the use of a P-channel MOSFET is disadvantageous in that a P-channel MOSFET has a higher,on,' resistance than an N-channel device, and thus is less suitable for driving a motor requiring a large current; that is, the use of a P-channel MOSFET results in a high running cost. In the headlamp cleaner control circuit of the invention, various techniques are employed to use an N-channel MOSFET as it were a P-channel MOSFET.

In addition, instead of the N-channel MOSFET, a PNP transistor may be employed. However, if a PNP transistor is used, it is necessary to increase the base current, and accordingly the PNP transistor generates a large quantity of heat. Hence, it is necessary to provide a heat sink for the transistor, which makes the overall unit bulky.

As is apparent from the above description, in the headlamp cleaner control circuit of the invention. one terminal of the cleaner motor is grounded at all times, and the other terminal is connected through the source electrode and the drain electrode of the N-channel MOSFET to the positive terminal of the power source mounted on the vehicle.

Furthermore, the headlamp cleaner control circuit. employing an N-channel MOSFET, is substantially resistive against corrosion due to moisture, humidity, etc., durable against vibration, and is scarcely affected by magnetic fields, and can be combined with the cleaner motor with a simple waterproof structure.

is - 19 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 is 19

Claims

1. A headlamp cleaner control circuit f or a headlamp cleaner system having a cleaner motor and cleaner switch, said control circuit comprising: an N-channel MOSFET having a source electrode connected to one terminal of said cleaner motor, the other terminal of which is grounded, and a drain electrode connected to the positive terminal of a power source; charging means connected between said source electrode of said MOSFET and the positive terminal of said power source through an ignition switch, said charging means being charged when said ignition switch is turned on; and timer means which starts a timing operation when said cleaner switch is turned on with said ignition switch turned on, to raise the level of the gate electrode of said MOSFET to render said MOSFET conductive, and which applies a charging voltage of said charging means to said gate electrode for a predetermined period of time lasting until said timer operation is ended, to maintain the level of said gate electrode higher than that of said source electrode.

- 1

2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 1 2 2. The headlamp cleaner control circuit of claim 1, wherein said charging means comprises a diode having an anode connected to said ignition switch and first capacitor having a first terminal connected to a cathode of said diode and a second terminal connected to said source of said MOSFET.

3. The headlamp cleaner control circuit of claim 2, wherein said timer means comprises a second capacitor and a resistor circuit connected to said second capacitor, a timing constant of said second capacitor and said resistor circuit determining said predetermined time.

4. The headlamp cleaner control circuit of claim 3, wherein said timer means further comprises transistor switch means for charging said second capacitor when said cleaner switch is in an off state and discharging said capacitor in response to said cleaner switch being placed in an on state.

5. The headlamp cleaner control circuit of claim 3, further comprising a power-on reset circuit for maintaining said MOSFET in an off state for a second predetermined period of time after said ignition switch is placed in an on state.

6. The headlamp cleaner control circuit of claim 5, wherein said power-on reset circuit comprises a third 21 - 3 3 4 1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 1 2 -W capacitor, said third capacitor having a longer charging time than said second capacitor.

7. The headlamp cleaner control circuit of claim 6, wherein said timer means comprises a first bipolar transistor connected between one terminal of said second capacitor and said gate of said MOSFET and a second bipolar transistor connected to said second capacitor to discharge said second capacitor when said cleaner switch is placed in said on state.

8. The headlamp cleaner control circuit of claim 6, wherein said timer means comprises a comparator, one terminal of said second capacitor being connected to a first input terminal of said comparator and one terminal of said third capacitor being connected to a second input terminal of said comparator, and an output of said comparator being connected to said gate of said MOSFET.

9. The headlamp cleaner control circuit of claim 8, further comprising a bipolar transistor connecting said output of said comparator to said gate of said MOSFET.

10. The headlamp cleaner control circuit of claim 8, wherein said timer means further comprises a bipolar transistor 3 4 1 2 3 4 5 1 2 3 4 5 1 2 3 4 1 2 3 4 1, connected to said second capacitor to discharge said second capacitor when said cleaner switch is placed in said on state.

11. The headlamp cleaner control circuit of claim 10, wherein said timer means further comprises a second comparator, said second comparator being connected to said second capacitor to discharge said second capacitor when said cleaner switch is placed in said on state.

12. The headlamp cleaner control circuit of claim 5, further comprising an interface circuit connected to said cleaner switch for starting operation of said timer means at said predetermined time period in response to said cleaner switch being placed in said on state.

13. The headlamp cleaner control circuit of claim 12, wherein said interface circuit comprises a fourth capacitor connected to said cleaner switch and said power source, said capacitor being charged when said cleaner switch is off and discharged when said cleaner switch is on.

14. The headlamp cleaner control circuit of claim 13, wherein said interface circuit further comprises a bipolar transistor connected between said fourth capacitor and a trigger input of said timer means.

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15. The headlamp cleaner control circuit of claim 13, wherein said interface circuit further comprises a comparator connected between said fourth capacitor and a trigger input of said timer means.

16. A headlamp cleaner control circuit according to claim 1, substantially as described with reference to any of the examples shown in figures 1 to 10 of the accompanying drawings.

Published 1992 at The Patent Office. Concept House. Cardiff Road, Newport. Gwent NP9 1 RH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach, Cross Keys. Newport, NP1 7HZ. Printed by Multiplex techniques lid. St Mary Cray, Kent.