Claims
- 1. An image forming apparatus comprising:
- a sample-and-hold circuit for sampling and holding a signal representative of detected laser beam power; and
- a current control circuit for controlling current applied to a laser device so that the sampled-and-held signal is driven to a value corresponding to a target laser beam power,
- wherein a time difference is provided between a time when the laser device is turned on and a time when said sample-and-hold circuit is set into a sampling mode.
- 2. An apparatus according to claim 1, wherein said apparatus comprises a laser power circuit for variably setting the target laser power in accordance with a signal from a target laser power setting means.
- 3. An apparatus according to claim 1, wherein said sample-and-hold circuit is set into a sampling mode only when said current control circuit turns laser beam emission ON.
- 4. An apparatus according to claim 1, wherein said apparatus includes a reset circuit which resets the sampled-and-held signal in a case where said image forming apparatus is in a standby mode.
- 5. An apparatus according to claim 4, wherein when said reset circuit is in a resetting mode, said sample-and-hold circuit is set into a holding mode.
- 6. An apparatus according to claim 1, further comprising a motor drive circuit which drives a scanning motor for rotating a polygonal mirror to scan the laser beam onto a photosensitive surface, wherein at least said laser drive circuit and said motor drive circuit are constructed on a monolithic drive IC using a bipolar device.
- 7. An apparatus according to claim 4, wherein said monolithic driver IC is installed onto a metal board on which the scanning motor is mountable.
- 8. A monolithic driver IC comprising:
- a sample-and-hold circuit for sampling and holding a signal representative of detected laser beam power; and
- a current control circuit for controlling current applied to a laser device so that the sampled-and-held signal is driven to a value corresponding to a target laser beam power;
- wherein a time difference is provided between a time when the laser device is turned on and a time when said sample-and-hold circuit is set into a sampling mode.
- 9. A monolithic driver IC according to claim 8, wherein said monolithic driver IC comprises a laser power circuit for variably setting the target laser power in accordance with a signal from an external device.
- 10. A monolithic driver IC according to claim 8, wherein said sample-and-hold circuit is set into a sampling mode only when said current control circuit turns laser beam emission ON.
- 11. A monolithic driver IC according to claim 8, wherein said monolithic driver IC includes a reset circuit which resets the sampled-and-held signal.
- 12. A monolithic driver IC according to claim 11, wherein when said reset circuit is in a resetting mode, said sample-and-hold circuit is set into a holding mode.
- 13. A monolithic driver IC according to claim 8, further comprising a motor drive circuit which drives a scanning motor for rotating a polygonal mirror to scan the laser beam onto a photosensitive surface.
- 14. An image forming apparatus comprising:
- a sample-and-hold circuit for sampling and holding a signal representative of detected laser beam power;
- a current control circuit for controlling current applied to a laser device so that the sampled-and-held signal is driven to a value corresponding to a target laser beam power; and
- a laser power abnormality detection circuit which detects a laser power abnormality and which controls said sample-and-hold circuit on the basis of a detection of laser power abnormality.
- 15. An apparatus according to claim 14, wherein said apparatus comprises a laser power circuit for variably setting the target laser power in accordance with a signal from a target laser power setting means.
- 16. An apparatus according to claim 14, wherein said sample-and-hold circuit is set into a sampling mode only when said current control circuit turns a laser beam emission ON.
- 17. An apparatus according to claim 14, wherein a time difference is provided between the time when said laser device is turned on and the time when said sample-and-hold circuit is set into the sampling mode.
- 18. An apparatus according to claim 14, wherein said apparatus includes a reset circuit which resets the sampled-and-held signal in a case where said image forming apparatus is in a standby mode.
- 19. An apparatus according to claim 18, wherein when said reset circuit is in a resetting mode, said sample-and-hold circuit is set into a holding mode.
- 20. An apparatus according to claim 14, further comprising a motor drive circuit which drives a scanning motor for rotating a polygonal mirror to scan the laser beam onto a photosensitive surface, wherein at least said laser drive circuit and said motor drive circuit are constructed on a monolithic driver IC using a bipolar device.
- 21. An apparatus according to claim 20, wherein said monolithic driver IC is installed onto a metal board on which the scanning motor is mountable.
- 22. A monolithic driver IC comprising:
- a sample-and-hold circuit for sampling and holding a signal representative of detected laser beam power;
- a current control circuit for controlling current applied to a laser device so that the sample-and-held signal is driven to a value corresponding to a target laser beam power; and
- a laser power abnormality detection circuit which detects a laser power abnormality and which controls said sample-and-hold circuit on the basis of a detection of laser power abnormality.
- 23. A monolithic driver IC according to claim 22, wherein said monolithic driver IC comprises a laser power circuit for variably setting the target laser power in accordance with a signal from an external device.
- 24. A monolithic driver IC according to claim 22, wherein said sample-and-hold circuit is set into a sampling mode only when said current control circuit turns laser beam emission ON.
- 25. A monolithic driver IC according to claim 22, wherein a time difference is provided between the time when said laser device is turned on and the time when said sample-and-hold circuit is set into the sampling mode.
- 26. A monolithic driver IC according to claim 22, wherein said monolithic driver IC includes a reset circuit which resets the sampled-and-held signal.
- 27. A monolithic driver IC according to claim 26, wherein when said reset circuit is in a resetting mode, said sample-and-hold circuit is set into a holding mode.
- 28. A monolithic driver IC according to claim 22, further comprising a motor drive circuit which drives a scanning motor for rotating a polygonal mirror to scan the laser beam onto a photosensitive surface.
Priority Claims (2)
Number |
Date |
Country |
Kind |
3-71699 |
Apr 1991 |
JPX |
|
3-71701 |
Apr 1991 |
JPX |
|
Parent Case Info
This application is a division of application Ser. No. 07/857,507 filed Mar. 25, 1992 U.S. Pat. No. 5,504,517, allowed.
US Referenced Citations (13)
Foreign Referenced Citations (4)
Number |
Date |
Country |
3618031 |
Jan 1987 |
DEX |
58-106622 |
Jun 1983 |
JPX |
59-067772 |
Apr 1984 |
JPX |
2229833 |
Oct 1990 |
GBX |
Divisions (1)
|
Number |
Date |
Country |
Parent |
857507 |
Mar 1992 |
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