Monitor circuit 16 has a divider network including transistor 52 having a base connected to the junction of resistors 53 and 54 between VDD and ground, a collector connected by resistor 55 to VDD and an emitter connected by resistor 56 to ground. The threshold clock 70 includes a timer 71 such as an NE , which is enabled by all three signals. The laser imaging apparatus of claim 1, including threshold circuit means for bringing said laser diode up to a threshold current before said image signal means modulates said laser diode. The laser diode 1 can, for example, be a 5 mW, nm laser diode. Their is a pin on the control connector which shows the crowbar protection circuit status. If, during this delay, the power supplies drop, diode provides a path to discharge capacitor rapidly to start the time delay over.

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These modules also have an on-board temperature sensor which will shut-down the output when the temperature exceeds a pre-set temperature.

SCR Thyristor Crowbar: overvoltage protection circuit

Typically a 5 volt rail may run with a 6. Applying Current to your Laser Diode: The laser diode has been used frequently as a light source in a variety of photographic applications. The output current is set by applying an analog signal to the current set pin on the control connector. The voltage at the gate of transistor 28 is set by the output of summing operational amp 29, and the amp 29 senses the voltage at the top of resistor The temperature of the laser diode 1 is monitored by a thermistor 3 which is mounted on a hybrid and has been disclosed in commonly assigned, copending U.

The SF6 series of CW drivers are used for laser marking, welding, soldering, and cutting applications.


Current Setpoint Absolute Accuracy: The thermistors are in series with a fixed resistor which is used to trim the total resistance to 5K. The thyristor crowbar circuit shown is very simple, only using a few components.

Current Setpoint Absolute Accuracy: This simple thyristor crowbar circuit can be very effective. The current set pin can be used for analogmodulation by applying sign wave, square wave or ramp signal. What is claimed is: The laser output power is monitored by back facet photodiode 2 which monitors the power on the back facet of the laser diode 1.

A faulty connection causing an open circuit to a negative temperature coefficient thermistor 3 can appear to be an under temperature condition and cause the TEC 87 FIG.

Practical Electronics/Crowbar circuit – Wikibooks, open books for an open world

For example, in the field of laser printing, a laser beam is focused through a lens and then scanned onto a photosensitive medium, such as film. An active crowbar is a crowbar that can remove the short circuit when the transient is over thus allowing the device to resume normal operation. This article is about the electrical circuit. Crowbar circuits are so named because their activation is similar in effect to dropping a crowbar across bus bars heavy duty power supply lines.

This invention relates in general to laser diodes and, more particularly, to an automatic power control circuit with means of protecting the laser crowbqr from over power, over or under temperature, and transient voltage or current spikes on power up and power down conditions.

The laser imaging apparatus of the present invention includes a laser diode for producing a laser light diide, an electrical power supply for supplying electrical power to said laser diode, a shunt circuit for shunting power around said laser diode, a laser power monitor for monitoring the laser light output of said laser diode, a thermal monitor for monitoring the temperature of said laser diode, lader power supply monitor crowvar monitoring the voltage power supply driving said laser diode and control means for controlling said crowar means to shunt croebar around said laser diode in response to one or more of the following signals: United States Patent On power up, capacitor 40 is charged through current path resistor 39, diode 38 and diode This cycle of thermal runaway can result in damage and failure of the laser diode 1.


Automatic frequency control circuit for coherent diversity reception. Other key protection features include a user adjustable driver current limit, over-current protection, overt-temperature protection and protection against reverse current transients.

An exemplary circuit is disclosed in commonly assigned, copending U. This will then provide a short circuit to ground, thereby protecting the circuitry that is being supplied form any damage and also blowing the fuse that will then remove the voltage from the series regulator. For purpose of explanation, only the top half of the power sequencer circuitry for the positive 12 volts VDD will be described.

Lwser allows capacitor 40 to be fully charged. A power-on reset circuit asserts the digital signal. Other signals which, when asserted lowcause the laser current to be shunted by the crowbar FET 34 are: They are also used in medical equipment and laser measurement equipment such as spectrometers, lidar and range finders.

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