Commonly used light source circuit in printing plate making

In the printing platemaking process, such as the illumination of the original, the electronic color separation scanning, the screening exposure recording, and the printing plate, etc., an appropriate electric light source needs to be selected.

At present, most of the light sources used in printing plates are gas discharge light sources, and there are also commonly used high-pressure gas discharge excitation laser light sources. This chapter mainly introduces commonly used electric light source circuits and laser light sources in printing plate making.

Section 1 commonly used electric light source circuit in the printing plate

一、Xenon lamp circuit

1. High voltage DC short arc xenon lamp circuit. Figure 4-1 shows the trigger circuit of a high-voltage DC short-arc xenon lamp with a power of 0.5-3kW. It is a spark oscillator type trigger circuit. T1 is a vibrator transformer with a transformer ratio of 1:130. T2 is a pulse transformer with a transformer ratio of 1:10.

The working principle of the circuit is: When the switch Q is closed, the circuit is connected to a 50V DC power supply, and a 50V DC voltage is applied to both ends of the lamp. At this time. Because the gas in the lamp has not been ionized, the lamp does not light.

When the normally open push button switch SB is pressed (about 3-5 s), the transducer transformer T1 is energized. Due to the magnetic field of the transformer core, the contact Z of the vibrator is disconnected. At this time, because the power supply is cut off, T1 is powered off, the iron core loses its magnetism, and the contact Z is re-closed by the bomb, causing the T1 to be energized again. jobs. So repeatedly in the T1 secondary induction 3-6kV high voltage, the capacitor C1 buffer capacitor, which is in parallel with the oscillator contact to eliminate contact spark, while also improving the primary waveform, C1 capacitance in 2 Between -4μF, withstand voltage 160-400V.

The high voltage generated by T1 secondary induction is charged every half cycle of the alternating voltage storage capacitor C2. When the voltage across the capacitor C reaches the breakdown voltage of the spark gap G, the spark gap breaks down and the capacitor C2 passes through the G to the pulse transformer T2. The primary performs high-frequency discharge and induces high-frequency voltages of up to 10,000 volts at the secondary of T2. Under this high-frequency high pressure, the helium gas in the tube generates spark discharge. If the trigger has enough energy to output, the discharge particle bombards the cathode to reach a certain high temperature, so that the cathode emits a large amount of electrons. At this time, the lamp will transition from the spark discharge to the arc discharge and the lamp will light up. When the Xenon lamp is ignited, the button switch SB should be released immediately to cut off the power supply of the trigger circuit so that the Xenon lamp can be powered by the 50 V DC power supply of the main circuit. The adjustable resistor RP is connected in series in the lamp circuit as a current limiter to adjust the operating current of the xenon lamp. C3 is a high frequency bypass capacitor. When the trigger is on, the secondary and lamp EL of the C3 and T2 constitute a high frequency circuit. Prevent high-frequency series DC power supply.

2. Exchange long xenon lamp circuit. AC long-arc xenon lamp triggers usually use spark-type triggers, and they can also use general-purpose oscillator-type triggers. Figure 4-2 shows the spark-type flip-flop circuit schematic. T1 is a high-voltage transformer that can raise 220V, 50Hz alternating current to 3.5-5kV high voltage. T2 is a pulse transformer with a transformer ratio of 1:7 to 1:10.

The working principle of the circuit is: When the power switch Q is turned on and the trigger button switch SB is pressed, the secondary inductive output of the high voltage transformer T1 is AC high voltage, and each half of the circumferential storage capacitor C1 is charged by R, and when C1 voltage rises to the spark gap G breakdown At voltage, G is broken down. At this time, the primary winding L1 of C1, G, and T2 constitutes a discharge loop. An arc discharge is formed when G breaks down to generate electric waves of various frequencies, and only high-frequency oscillations having the same frequency as the L1 and C1 oscillation circuits can obtain resonance at the resonance frequency of f=1/2Ï€(L1C1)1/2 It can be boosted to tens of thousands volts by the pulse transformer T2, so that the lamp EL breaks down and ionizes under high-frequency and high-voltage; when the output energy of the trigger is sufficient, the lamp is converted into arc discharge, and the xenon lamp is ignited. When the Xenon lamp is turned on, the button switch SB is released and the trigger power is cut off. At this time, the Xenon lamp is powered by 220V AC power. The choke L3 acts as a current limiter in the lamp circuit. In order to prevent the transformer T2 from heating too high, the current limiting resistor R is connected in series in the circuit, and the capacitor C2 is a high-frequency bypass capacitor to prevent the high-frequency series 220V power supply.

3. Pulsed xenon lamp circuit. The pulse xenon lamp tube is made of quartz glass, and two xenon nickel electrodes are sealed on both ends of the tube. The tube is filled with xenon gas and the gas pressure is 100-300 mmHg. The outer wall of the lamp tube is coated with a band-shaped metal film or a wire is wound along the lamp tube. The spiral shaped ignition pole is connected to the high voltage output of the pulse transformer. Because the xenon lamp is a pulse output, it can emit extremely strong light in a very short time, and the brightness is extremely high. Because its power spectrum is close to that of sunlight, it is particularly suitable for printing color separation plates. Due to the light intensity and high exposure speed, it is more suitable for direct screen color separation. The pulsed xenon lamp can also be used as a pump source pulsed xenon lamp trigger circuit for a dynamic holographic photographing laser, as shown in Figure 4-3.

The circuit consists of three parts:

1 The voltage regulator circuit consists of a current limiting resistor R6 and a Zener diode VZ. The voltage Ub is a DC power supply for the single junction transistor VU.

2 consists of resistors R1, R2, R3, R4, capacitor C3 and a single crystal tube VU to form a relaxation oscillation circuit for generating a trigger pulse to control the thyristor VT timing conduction.

3 by the resistor R5, capacitor C1, crystal reservoir tube VT and the primary winding of the pulse transformer T capacitor C1 charge and discharge circuit, so that the secondary pulse transformer T induced high-voltage pulse, so that the lamp helium breakdown ionization.

The working principle of the circuit can be analyzed as follows:

When the power is turned on, three DC power supplies (GH, AB, EF) supply power at the same time, but the lamp does not light up. The high voltage direct current power source EF input by the main circuit charges the capacitor group C2; the charging power source AB passes through the resistor R, and the coil L1 charges the capacitor C1. The voltage regulator Ub charges the capacitor C3 through R3 and R4. When the voltage U across the capacitor C3 gradually rises and Ue<Up, the voltage U of the output resistor R1 of the single junction transistor is zero, and the thyristor VT is at End state. When Ue>Up, the single-junction transistor is turned on, and the conduction current is Ie, then UR1=eR1. When UR1 is greater than the VT conduction voltage of the thyristor, VT is turned on. At this time, the charge accumulating on C1 will be discharged through the VT and L1 loops, so that the secondary inductive output of the pulse transformer T will output a high frequency and high voltage, causing the lamp to break down. At the same time, the main circuit's high-voltage energy storage capacitor discharges the xenon lamp through the lamp discharge. When the discharge current of C1 is lower than the thyristor VT's holding current, VT is automatically turned off. This completes a trigger pulse. The button switch SB can replace VT. Realize manual control as an emergency.

4. Double lamp circuit. There are two lamps in the original lighting. The light source is a tubular deuterium lamp with a power of 1.5kW, which is usually divided into four groups by the same two groups.

Dual-lamp light circuit shown in Figure 4-4, EL1, EL2 in the figure are two tubular xenon lamps; CF is a vibrator type high-frequency high-voltage trigger; TA is a xenon ballast; R is a starting current limiting resistor, resistance 8Ω; 6M, 7M cooling fan. The control of exposure time is manual and automatic; DG is an automatic switch and SA is a manual switch.

The working principle of the circuit is: When the switch SA closes, the relay KA4 pulls in, the normally open contact KA4 is closed, the contactor KM9 is energized and the contactor is closed, the KM9 normally open contact is closed, the cooling fan 6M, 7M operates, and the trigger circuit Begin to turn on, the current flow is:

Power supply B → KM9 (normally closed) → KT (normally closed contact) → phase → L1 (vibrator coil) → L2 (high voltage transformer primary coil) → 0

The vibrator G is disconnected from the circuit by the vibrator being attracted by the iron core in the loop L1. Since the circuit is powered off, the vibrator contact is reconnected to the circuit by means of the spring, and the vibration is thus repeated. When the vibrator is disconnected, the power supply charges the resonant capacitor C3. When the vibrator is turned on, the charge on C3 is discharged through L2. The resonant frequency is determined by the formula f=1/2Ï€(L2C2)1/2. Therefore, the primary winding L2 of the transformer T passes a high-frequency current, and such a high-frequency current generates a high-frequency high-voltage electromotive force in the secondary winding L3. It excites the xenon lamps EL1 and EL2 to ionize the gas in the tube. Since xenon lamps EL1 and EL2 are connected in series between the phases B and C, the xenon lamp is turned on and ignited at a voltage of 300V. The current limiting resistor R is connected in series with the ballast coil TA to limit the current. When the TA flows enough operating current, the secondary current induces the relay KA6 to pull in. The KA6 normally open contact closes the time relay KT. Work, so that the normally closed contact delays the disconnection of the phase C, and KA3 normally opens the contact and closes the end of the light source to the neutral line. At this point, the xenon lamp enters normal operation. The operating current flow is:

Power supply B → KM9 (normally closed) → EL2 → EL1 → TA → KA3 (normally closed) → 0

The function of the time delay relay KT is to allow the current in the current limiter TA to stabilize for a period of time, then disconnect the trigger circuit, turn on the relay KA3 to make the neon lamp work normally, and the capacitor C5 is the high frequency bypass capacitor of the lamp EL2. , C2, C4 is the high-frequency bypass capacitor of the lamp EL1.

Second, the deuterium lamp circuit

Xenon lamp is a new type of electric light source used in printing plate making. It is a metal halide gas discharge light source. The tube is filled with elements such as neon, xenon, mercury and iodine, also called xenon lamp. The xenon lamp has a long tubular shape with a round shape in between. Light color near the xenon lamp, luminous efficiency is about 1 times higher than xenon lamp about 801m/W, the brightness is extremely high, the color temperature is in 5000-6000K.

Since the deuterium lamp has a low ionization potential, the trigger voltage is lower than that of the deuterium lamp and it is easier to trigger the ignition. Its trigger circuit is relatively simple, usually using a vibrator trigger circuit.

A 1-3kW xenon lamp trigger circuit with output power is shown in Figure 4-5. In the figure, T is a high-frequency high-voltage transformer, L1 is a vibrator coil, L4 is a ballast, C1 is a resonant capacitor, and it forms a resonant circuit with the primary winding L2 of a high-frequency transformer, KA is a current relay, and C2 is a high-frequency bypass capacitor .

The working principle of the circuit is: When the switch Q is turned on, the AC voltage of 220V is applied to both ends of the lamp EL, but this voltage does not make the deuterium lamp lit. When the power is turned on, when the electromagnetic vibrator contact G is disconnected, the power supply charges C1; when G is turned on, the resonance frequency is f=1/2Ï€(C1L2)1/2, and the high-frequency current in L2 is high. The high-frequency high-voltage is induced in the sub-winding L3 of the high-frequency transformer T and is applied to the two ends of the lamp through the high-frequency bypass capacitor C2 to make the xenon lamp start to glow. Due to the rapid temperature rise of the lamp electrode, it gradually transitions to arc discharge. When the current rises to a certain value, the current relay KA acts, and its normally closed contact disconnects the trigger circuit power. Under the action of the AC 220V voltage, the xenon lamp enters the normal working state. The high-frequency bypass capacitor C2 is used to prevent high-frequency series power supply.



Source: "Circuit and Control of Printing Devices"