JPS6349911A - Interruption circuit - Google Patents

Abstract

PURPOSE:To surely interrupt current by detecting abnormal current flowing into a heater for a fixing device or the like at the time of non-driving of the heater. CONSTITUTION:A fixing device circuits is constituted by connecting a current transformer T1, a contact rl1 for a relay RL1, a thermal protector TP1, a fixing device heater H1, a TRIAC Q7 for switching the heater 1H, and a serial circuit for a coil L1 between terminals 2 and 3 and the IRIAC Q7 is driven by a solid-state relay SSR1 including a zero crossing detecting circuit 10. At that time, comparators CP1, CP2 are connected to a secondary side of the current transformer T1 to detect the current flowing into the heater H1. At the time of non-driving, i.e. when a driving signal to the terminal 1 is 0V (at the time of off of the TRIAC Q7), an abnormal current detecting circuit through a transistor (TR) Q2 is constituted. At the time of detecting the abnormal current, a TR Q5 is driven and the contact rl1 of the relay RL1 is opened to protect it.

Description

[Detailed description of the invention] [Industrial application field] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disconnection circuit.

[Prior Art] For example, in an image forming apparatus, a fixing device is used to fuse a toner image transferred from the surface of a photosensitive drum to a transfer material.

[Problems to be Solved by the Invention] Conventionally, in this type of fuser, if the semiconductor that switches the fuser heater breaks down in short mode,
An abnormal current flows through the fixing device heater, and the fixing device reaches a high temperature, which may damage the fixing device itself and the image forming apparatus.

Note that this type of semiconductor short-circuit damage is more likely to occur in a unidirectional short mode than in a bidirectional short mode.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cutoff circuit that can eliminate the drawbacks of the conventional example described above and can reliably cut off the current flowing to the fixing device when an abnormal current occurs, for example.

[Means for Solving the Problems] The present invention includes six cutoff means for cutting off the current flowing to the heater of the fixing device, etc., and a device for blocking the abnormal current flowing to the heater of the fixing device, etc. when the heater of the fixing device, etc. is not driven. a detection means for detecting; and a constant i when an abnormal current is detected by this detection means.
and means for controlling the interrupting means to interrupt the current flowing to the heater of the heater.

[Function] According to the present invention, abnormal current flowing through the heater of the fixing device or the like is detected when the heater of the fixing device or the like is not driven, and the current flowing through the heater of the fixing device or the like is interrupted.

[Example] An embodiment of the present invention will be described below.

FIG. 1 shows the configuration of the fuser circuit. As shown in Figure 1, terminal 2 is the primary terminal 15.16 of current transformer T1.
is connected to the make side of contact roll of relay RLI through contact rj! 1 common side is thermal protector T
PI is connected to the A1 side of the triac Q7 for switching the heater H1 via the fuser heater H1, and a spark killer SQI is connected between the make side and the common side of the contact rfL1.

Terminal 3 is connected to A of triac q7 via carp j%zL1.
2 side, end, child 3 is also spark killer SQ2
It is connected to the Al side of triac q7 via. A resistor R17 is connected between the A2 side of the triac q7 and the gate G, and the gate G of the triac Q7 is a solid state relay 5SRI with a built-in zero-cross detection circuit IO.
A of triac q7,
The 1 side is connected to the output terminal 14 of the old Solid Steadley SS via a resistor R16. A commercial AC power source Vo (not shown) is applied between terminals 2 and 3.

One terminal 17 on the secondary side of the current transformer TI is connected to the inverting input terminal 19 of the comparator CPI and the comparator C
It is connected to the non-inverting input terminal 24 of P2.

A resistor R1 is connected between the secondary side terminals 17 and 18 of the current transformer T1, and the other terminal 18 on the secondary side is connected to the resistor R3.
, R2 to the terminal 4, and a resistor R4,
It is connected to a reference potential (hereinafter referred to as GND) via R5. A DC power source E0 is applied to the terminal 4. The connection point between the resistors R3 and R2 is connected to the non-inverting input terminal 20 of the co-vaginator CP1, and a capacitor C1 is connected in parallel to the resistor R3. The connection point between the resistors R4 and R'5 is connected to the inverting input terminal 24 of the comparator CP2O, and the resistor R4
A capacitor C3 is connected in parallel with .

Furthermore, the secondary side terminal 18 of the current transformer TI is connected to the guard of the Zener diode 2D2 and also to the terminal 4 via a resistor R9. The anode of the Zener diode ZD2 is connected to GND, and a capacitor c! is connected in parallel with the Zener diode ZD2. i is connected.

The output terminal 21 of the comparator CPI is the comparator Cf
'2, and the connection point is connected to the base of the NPN transistor q1 and the resistor R6.
It is connected to terminal 4 via. The positive power input terminals 22 of the comparators CPI and CF2 are connected to terminal 4, the negative power input terminals 23 are connected to GND, and there is an NPN connection between the positive power supply 22 and the negative power supply 23o'.
The emitter of transistor Ql is connected to GND, and its collector is connected to terminal 4 via resistor R7 and to the base of NPN transistor q2 via resistor R8.

The base of the NPN transistor Q2 is connected to GND via the capacitor C4, and is also connected to the anode of the diode D4, and the emitter thereof is connected to the cathode of the Zener diode 201 and the Zener diode zD.
The anode of L is connected to GND. The collector of NPN transistor q2 is connected to the base of PNP transistor q3 via resistor RIO.

The emitter of the PNP transistor q3 is connected to the terminal 4, and the base thereof is connected to the terminal 4 via a resistor R11, and also to the cathode of the diode DI and the collector of the Nf'N transistor q4 via a resistor R12. The collector of PNP transistor q3 is resistor R13,
Connected to GND via R14. Resistance R13.

The connection point of R14 is connected to the base of NPN transistor Q4 and is also directly connected to GND via capacitor C6.

The anode of diode DI is connected to terminal 4 via resistor R15.
and the anode of diode 02. The cathode of diode D2 is connected to the base of NPN transistor Q5, and the emitter of NPN transistor Q5 is connected to GND. The collector of NPN transistor Q5 is connected to the anode of diode D3, the cathode of diode D3 is connected to terminal 4, and the NPN
N) - A relay R is installed between the collector of transistor q5 and terminal 4 to cut off the current flowing to heater H1 in the event of an abnormality.
LI is connected.

Terminal 1 is a terminal to which a level signal for controlling on/off of fixing heater H1 is input, and is connected to the base of NPN transistor Q6 via resistor R19.

NPN) - the base of transistor Q6 is also connected to resistor R20
Its emitter is connected to GND, and its collector is connected to the cathode of diode D4 and to the input side terminal 12 of solid state relay 5SRI. solid state relay 5sr
The input side terminal 11 of I is connected to the terminal 4 via a resistor R18.

Next, the detection levels of the two comparators CPI, CP, and 2 will be explained with reference to FIGS. 2 and 3.

The reference voltages of the comparators CPI and CF2 are set to the plus (non-inverting) side and the minus (inverting) side, respectively, and the values of the reference voltages VIN1. VIN2 is respectively s vZD2+vlNl+vlN2 is v, N2 <vZ
D2 <vlN.

There is a relationship between

Comparators CPI and CP2 are oven collector outputs, and their outputs vCPl+vCP2 (comparison input (inverting side for CPI, non-inverting side for CF2) is VIN
0) respectively, V INO < V INI・V IN2 < V IN
When O, it becomes an oven, and V +s+ < V INOI V INO < V 1
It operates so that it becomes OV when it is 82.

Output terminal 21 of comparator CPI and comparator CP
When the output terminals 26 of 2 are connected as shown by the dotted lines in FIG. 2, the voltage at the connection point is vcp. becomes an oven only when V IN2 < V + Na < V INI.

When the sine wave shown in FIG. 3(a) is input to VINO, the above Vcp+ (single), VCP2 (single), V
The voltage waveforms of cpo are shown in Figure 3 (b) and (c), respectively.
, shown in (d).

Next, the operation of the circuit shown in FIG. 1 will be explained.

In the normal state, when terminal 1 is O [V], transistor q6 is turned off, so solid state relay 5SR
Light emitting element 0 (connected between input terminals 11 and 12) of I
No current flows to 10, solid state relay 5SRI
is off, so no gate current flows through the triac Q7, the triac Q7 is turned off, and no current flows through the primary side of the current transformer T1 even if commercial AC power is applied between terminals 2 and 3.

When no current flows through the primary side of current transformer T1,
No voltage is induced on the secondary side of current transformer T1,
As described above, the voltage VINO of the inverting input terminal 19 of the comparator CPI and the non-inverting input terminal 24 of the comparator CP2 is V I82 < V INO= V 202 < V
INI, in this case comparator CP1. Since both outputs of CP2 are ovens, they are connected to N through resistor R6.
A base current flows through the PN transistor Q1, turning on the NPN transistor Q1. NPN transistor Q1
When turned on, the base voltage of the NPN transistor Q2 becomes close to 0 [V], so the NPN transistor q2 is turned off. When NPN transistor Q2 turns off, PNP transistor Q3. Since no base current flows through NPN transistor Q4, PNP transistor Q3. NPN) transistor q4 turns off, base current flows through resistor R15 and diode D2 to FiPN) transistor Q5, and NPN transistor q
Turn on 5. When the NPN transistor Q5 is turned on, a current flows through the relay RLI, the relay RLI is turned on, and the contact rfL1 of the relay -&L1 is switched to the dotted line side (meter side) in FIG. 1.

As mentioned above, if the voltage at terminal 1 continues to be O [V], triac Q7 is in the OFF state, so relay R
Even if the LI contact rfl switches to the dotted line side, no current flows to the primary side of the current transformer TI, and the above state is ilM.
be done.

In this state, when a signal (positive voltage) to turn on the fuser is applied to terminal 1, the NPN
A base current flows through the transistor q6, and the NPN transistor q6 is turned on. When NPN transistor q6 is turned on, the base of NPN transistor q2 is connected to diode D4. Since the collector and emitter of the NPN transistor Q6 are connected to GND, the NPN transistor Q2 is turned off, and as described above, the
3. NPN transistor q4 is turned off, NPN transistor Q5 is turned on, and relay RLI continues to be on. On the other hand, when the NPN transistor q6 turns on, the solid state relay is activated through the resistor R18.
Since current flows through the light emitting element 010 of 5SRI, solid state relay 5SRI is turned on, and triac q7
A gate current flows through. Triac Q7 is turned on by the gate current flowing, and terminal 2 - primary side of current transformer T1 - contact of relay RLL 11 - thermal protector TPI constant heater old - triac q7
- A main current loop between coil L1 and terminal 3 is formed, and current flows to fuser heater H1.

What has been described above is the circuit operation under normal conditions.Next, the operation under abnormal conditions will be explained with reference to the time charts shown in FIGS. 4 and 5.

FIG. 4 is a time chart in the case of a breakdown in which the triac q7 becomes conductive in both directions, and FIG. 5 is a time chart in the case in which a breakdown occurs in which the triac q7 becomes conductive in only one direction.

If triac q7 breaks down to bidirectional conduction while a voltage close to 0 [V] is applied to terminal 1, the voltage on the inverting input terminal side of comparator CPI and the voltage on the non-inverting input terminal side of comparator CP2 VIN
O becomes as shown in FIG. 4(b), and as described above, NPN only when V tNt < V sNo < V 181 )-transistor q1 is turned on, and as shown in FIG.
It operates as shown in C). .

On the other hand, since Nf'N transistor QB is off, t41'N transistor q
No current flows between the collector and emitter of Q6, so when NPN transistor Q1 is off, resistor R7,
Capacitor C4 is charged via R8, and when NPN transistor Q1 is on, capacitor C4 is discharged via resistor R8 and NPN transistor Ql. This state is shown in FIG. 4(d). As shown in FIG. 4(1), the voltage of capacitor C4 is the voltage of NPN transistor q1,
As it is repeatedly turned on and off, it gradually rises and reaches a voltage close to the sum of the Zener voltage of the Zener diode Z[11 and the base-emitter voltage of the NPN transistor Q2 (this voltage is called o*os). N
The base current flows through the PN transistor q2, and the NPN
Transistor q2 is turned on. When NPN transistor Q2 turns on, resistor RIO, NPN transistor q
Base 7 current flows through the PNP transistor Q3 through the PNP transistor Q3, turning on the PNP transistor Q3. PNP
) By turning on transistor q3, PNP transistor q3. The base current of the NPN transistor Q4 flows through the resistor R13, and the NPN transistor Q4
turns on. When NPN transistor q4 turns on, resistor R12.

Since the base current of PNP transistor q3 flows through NPN transistor Q4, a circuit consisting of PNP transistor q3 and NPN transistor Q4,
operates as a self-holding circuit, and the NPN transistor q
2 remains on even if it is turned off. On the other hand, when NPN transistor Q4 turns on, NPN ) transistor q5
Since the base current of is cut off, the NPN transistor Q5 is turned off, the relay RLI is also turned off, the contact r11 of the relay RLI is restored to the state shown by the solid line in FIG. 1, and the current of the fuser heater H1 is cut off.

As shown in FIG.
G, H (that is, NPN) - the time it takes for transistor Q2 to turn on is only longer than in the case of bidirectional conduction breakdown, and other circuit operations are the same as described above. The same is true for .

As mentioned above, since the circuit composed of the PNP transistor q3 and the NPN transistor Q4 is a self-holding circuit, no current flows to the primary side of the current transformer T1, resulting in V INO" V 202, and the NPN transistor Q1 is Turn on, NPN
Even if transistor Q2 is off, it remains on f4! Continue.

As described above, by adding an abnormal current detection circuit using a current transformer and two comparators to the main current circuit including the fuser heater, the surrounding components and, by extension, the entire device can be protected from heat generation due to the abnormal current of the fuser heater. be able to. In addition, when detection is performed using two comparators, when the triac Q7 causes breakdown of unidirectional conduction, the current value is smaller than that explained in Fig. 5, and the visa is shown in Fig. 6 (b). , (d), the NPN l-transistor Q1 is as shown in Fig. 6 (C
), it turns on and off as shown in (e), charges the capacitor C4, and has the effect of restoring the relay RLI as described above. However, in the case of detection by one comparator, for example, in the case of detection by only comparator CP1, the detection of abnormal current in the direction of FIG. 6(f) is NP! as shown in FIG. 6(g). 1 This is possible by turning on and off the transistor Q1, but in the case of an abnormal current in the direction shown in Fig. 6 (h),
As shown in FIG. 6(i), since the NPN transistor Q1 remains off, detection is impossible and the relay RLI is not restored.

[Effects of the Invention] As described above, according to the present invention, it is possible to reliably interrupt the current flowing to the heater of the fixing device or the like when an abnormal current occurs.

[Brief explanation of drawings]

1 is a circuit diagram of an embodiment of the present invention; FIG. 2 is a circuit diagram for explaining the detection section of the comparator shown in FIG. 1; FIG. 3 is a time chart for explaining FIG. 2; 5 is a time chart for explaining a part of the circuit operation of FIG. 1, and FIG. 6 is a time chart for explaining the effect. CPI, CF2... Comparator, 01~C6...
・Capacitor, Q1-Q6...Transistor, Q7...Triac, R1-RIO...Resistor, D1-D4...Diode, XDI, ZD2...Zener diode, RLI
(rfL 1) "・Relay (contact), TPI... Thermal protector, Hl... Fuser, 5SRI... Solid state relay, Ll... Coil, SQL, SQ2... Spark killer, T1... ...Current transformer.

Claims (1)

[Scope of Claims] A cutoff means for cutting off current flowing through a heater of the fixing device, etc.; a detection means for detecting an abnormal current flowing through the heater of the fixing device, etc. when the heater of the fixing device, etc. is not driven; A cutoff circuit comprising means for controlling said cutoff means to cut off current flowing to a heater of said fixing device or the like when an abnormal current is detected by said detection means.