JP2001057776A - Rush current preventive circuit in power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce wasteful power consumption and cost of a power supply circuit, using a rush current preventive circuit. SOLUTION: A normally-open contact Sy1 of a relay RL which operates, when the charge value of the smoothing capacitor C1 of a rectifying/smoothing circuit 3 reaches a prescribed value is inserted in one L of feeder lines L and N, between a power supply switch 2 and the rectifying/smoothing circuit 3. Two heaters HR1 and HR2, of which a heater circuit is composed, are connected in series with each other and are connected in parallel with the normally- open contact Sy1 of the relay RL. A connection point (e) between the two heaters is connected to the other feeder line N between the power supply switch 2 and the rectifying/smoothing circuit 3 via an energizing control circuit 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rush current prevention circuit in a power supply circuit in which a rectifying / smoothing circuit of a capacitor input type and a heater circuit are provided in parallel to an AC power supply via a power switch.

[0002]

2. Description of the Related Art For example, an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile machine or the like has a load to which a high DC voltage is applied such as a charging charger or a transfer charger and a heater such as a fixing device heater. There is a load to which an alternating current is applied. In order to generate a DC high voltage, generally, a rectifying and smoothing circuit of a capacitor input type rectifies and smoothes an alternating current from a commercial power supply and converts it to DC, and further generates a high voltage DC by a switching regulator or a DC-DC converter. A circuit is used.

In such a power supply circuit in which a capacitor input type rectifying / smoothing circuit is connected to an AC power supply, a rush current (rush current) is required to charge a large-capacity empty capacitor of the rectifying / smoothing circuit when the AC power supply is turned on. Flows. If such a rush current flows, there is a risk that circuit elements will be burned or deteriorated and noise will be generated. In order to reduce the rush current, a resistor and a switch circuit (relay, (Including a triac, a thyristor, etc.).

FIG. 4 shows such a capacitor input type rectifying / smoothing circuit and a switching regulator.
1 shows a conventional example of a power supply circuit of an image forming apparatus provided with a heater circuit and an inrush current prevention circuit.

This power supply circuit comprises an AC current input section comprising an AC plug 1 and a power switch 2 formed by bipolar switches SW1 and SW2, and a full-wave rectifier circuit (diode bridge).
A rectifying / smoothing circuit 3 including a BR and a smoothing capacitor C1,
A switching regulator 4 including a transformer T, a switching element Q such as a transistor, and a control IC 10;
A relay RL, a normally-open contact Sy1 thereof, and an inrush current prevention circuit 5 comprising a resistor R1 for preventing inrush current, and a parallel connection 2
And a heater circuit 6 to which an energization control circuit 11 using a triac is connected in series with the heaters HR1 and HR2. The heater circuit 6 includes an AC plug 1 serving as an AC power supply.
Are connected in parallel with the rectifying / smoothing circuit 3 via the power switch 2.

When the AC plug 1 is attached to the outlet of the commercial power supply and the power switch 2 is turned on (ON), an alternating current flows through the resistor R1 of the inrush current prevention circuit 5 (the normally open contact Sy1 of the relay RL is turned off). Rectified by the full-wave rectifier circuit BR (because it is open), and a large-capacity smoothing capacitor C
Charge 1 slowly. Then, when the terminal voltage of the capacitor C1 reaches a predetermined voltage, the voltage applied to the control IC via the starting resistor R2 reaches the starting voltage, the control IC 10 starts and outputs a switching pulse,
The on / off control of the switching element Q is started.

As a result, the primary winding L1 of the transformer T
, A current flows intermittently, and the switching regulator 4 enters an operating state. A high-voltage pulse is generated in each of the secondary windings L2 and L3 of the transformer T. The high-voltage pulse is rectified and smoothed by the diode D2 and the capacitor C4 or the diode D3 and the capacitor C5, respectively, to output DC high voltages Va and Vb. .

Further, the relay RL is activated by the voltage Vs obtained by rectifying and smoothing the voltage generated in the internal output secondary winding L4 by the diode D4 and the capacitor C2. Thereby, the normally open contact Sy1 of the relay RL is closed, and the current from the AC power supply flows directly to the rectifier circuit BR. Also, the control IC 10 continues to operate according to the voltage Vs. Diode D1, capacitor C3, resistor R
Reference numeral 3 denotes a snubber circuit that absorbs an abnormal voltage generated in the primary winding L1 by turning on / off the switching element Q.

The heaters HR1 and HR2 are provided with a heater ON / O
By controlling the conduction time (conduction angle) of the triac of the conduction control circuit 11 for each cycle or half cycle of the AC voltage via the photocoupler circuit 12 by the FF signal, on / off and execution current are controlled. The heating temperature is controlled.

According to this power supply circuit, the inrush current prevention circuit 5 is provided, and after the power switch 2 is turned on,
Until the large-capacity capacitor C1 is charged to a predetermined voltage, the input AC current flows through the resistor R1 to the full-wave rectifier circuit BR.
Rush current is reduced. Then, when the relay Rl is operated and its normally open contact Sy1 is closed, the input AC current flows directly to the full-wave rectifier circuit BR, and the rated operation is performed.

That is, the capacitor C of the rectifying / smoothing circuit 3
As 1 is charged, the impedance of the rectifying / smoothing circuit 3 as viewed from the input side increases, and an excessive current due to the input AC current does not flow. Therefore, the resistor R1 of the inrush current prevention circuit 5 becomes unnecessary. Therefore, the normally open contact Sy1 is closed by the operation of the relay RL to prevent wasteful power consumption by the resistor R1.

[0012]

However, in such a conventional inrush current prevention circuit 5, if the power rating of the resistor R1 is large in proportion to the capacitance of the capacitor C1 of the rectifying / smoothing circuit 3, it is necessary to use one. No. Therefore, there is a problem that not only the cost is increased but also the power loss is increased and the problem of heat generation is caused.

The present invention solves such a problem,
It is an object of the present invention to reduce costs and prevent wasteful power consumption by not using a resistor or having a small power rating in an inrush current prevention circuit.

[0014]

SUMMARY OF THE INVENTION The present invention provides a power supply circuit in which a rectifying / smoothing circuit and a heater circuit are provided in parallel with an AC power supply via a power supply switch. The circuit is configured as follows.

The heater circuit is constituted by inserting a normally open contact of a relay which operates when a predetermined amount of a smoothing capacitor of the rectifying / smoothing circuit is charged into one power supply line between the power switch and the rectifying / smoothing circuit. The two heaters are connected in series and connected in parallel to the normally open contact of the relay.
The connection point of the heaters is connected to the other power supply line between the power switch and the rectifying / smoothing circuit via the power supply control circuit.

Alternatively, a normally open contact of a switching contact of a relay, which is activated when a predetermined amount of a smoothing capacitor of the rectifying / smoothing circuit is charged, is inserted into one power supply line between the power switch and the rectifying / smoothing circuit. The heater constituting the heater circuit and a resistor for preventing inrush current are connected in series, and connected between the one power supply line and the normally closed contact of the switching contact of the relay, and the heater and the resistor are connected. May be connected to the other power supply line between the power switch and the rectifying / smoothing circuit via a conduction control circuit.

The heater may be directly connected between the one power supply line and a normally closed contact of the switching contact of the relay, omitting the resistor for preventing the inrush current.

As described above, when the power supply circuit is started after the power switch is turned on, the heater of the heater circuit is used in place of all or a part of the inrush current prevention resistor, thereby eliminating the need for the inrush current prevention resistor. In other words, the power rating is rather small, and cost reduction and wasteful power consumption can be reduced. Further, current flows to the heater when the power supply circuit is started, and the heater changes from a cold state to a preheated state. Therefore, the resistance value increases, and the rush current at the time of starting the heater circuit can be reduced.

In the rush current prevention circuit in these power supply circuits, the power supply circuit may be a power supply circuit in which a switching regulator for generating a high DC voltage is connected to the output side of the rectifying and smoothing circuit. Further, the power supply circuit may be a power supply circuit for an electrophotographic image forming apparatus, and the heater may be a heater for a fixing device.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of a power supply circuit provided with an inrush current prevention circuit according to the present invention. The same parts as those in the conventional example shown in FIG. Yes, and their explanation is omitted.

The power supply circuit of the first embodiment shown in FIG. 1 is different from the conventional power supply circuit shown in FIG.
The only difference is that an inrush current prevention circuit 15 is formed instead of the inrush current prevention circuit 5.

The rush current preventing circuit 15 eliminates the conventional resistor R1 for preventing rush current and connects a rectifying / smoothing circuit to one of the power supply lines L (on the side of the switch SW1) between the power switch 2 and the rectifying / smoothing circuit 3. 3 through the normally open contact Sy1 of the relay RL that is activated when a predetermined amount of the smoothing capacitor C1 is charged, and the two heaters HR1,
HR2 is connected in series, and the normally open contact Sy1 of the relay RL is connected.
And connected in parallel.

The heater circuit connects the connection point e between the two heaters HR1 and HR2 to the other (switch SW) between the power switch 2 and the rectifying / smoothing circuit 3 via the conduction control circuit 11.
2) to the power supply line N.

Next, a description will be given of the flow of current from the time when the power switch 2 is turned on to the time when the power supply switch 2 shifts to the normal operation. In the initial state, the relay RL is not operated, and the normally open contact Sy1 is open as shown in the figure. So, A
When the power switch 2 is turned on in a state where the C plug 1 is attached to the outlet of the commercial power supply, the switches SW1 and SW2 of the power switch 2 are turned on, and the heaters HR1 and HR2 of the inrush current prevention circuit 15 are connected. Rectifying smoothing circuit 3
A current flows through each connection point of the diode bridge (a, b, c, d).

When one of the AC power supply lines N and L has a positive value on the side of the power supply line L, L → HR1 → H shown in FIG.
A current flows through the path of R2 → a → d → C1 → b → c → N,
Electric charge is charged in the smoothing capacitor C1.

When the other power supply line N side is +, N
A current flows through a path of → c → d → C1 → b → a → HR2 → HR1 → L, and charges the smoothing capacitor C1.
In any case, since the current flows through the heaters HR1 and HR2 having resistance in series, there is sufficient resistance, so that an excessive current does not flow through the circuit and an inrush current is prevented from flowing.

After a while in this state, the capacitor C1 is charged with electric charge, and the electric charge starts to be charged in the capacitor C2 through the starting resistor R2. The voltage due to the electric charge charged in the capacitor C2 is equal to the control IC 10
, The switching operation of the switching element Q is started, and the current flowing through the primary winding L1 of the transformer T is interrupted. That is, the switching regulator 4 starts operating.

Thus, the secondary winding L of the transformer T
As described above, the DC high voltages Va and Vb are generated on the L2 and L3 sides, and the voltage Vs is generated by rectifying and smoothing the voltage generated in the internal output secondary winding L4 by the diode D4 and the capacitor C2.

The voltage Vs activates the relay RL, closing its normally open contact Sy1. That is, the AC input that has passed through the power switch 2 flows directly to the rectifying and smoothing circuit, thereby preventing wasteful power consumption. Also, two heaters H
R1 and HR2 are connected between the power supply lines L and N via the power supply control circuit 11 in a parallel state in which both ends are connected to each other. When the power supply control circuit 11 is activated, the operation as a normal heater is performed. start.

According to this embodiment, since a resistor for preventing inrush current having a large current rating in the conventional inrush current prevention circuit becomes unnecessary, cost can be reduced and wasteful power consumption due to the resistor can be reduced. It can also be prevented. Further, when the power supply circuit is started, a current flows through the heaters HR1 and HR2 of the heater circuit 6, and the heaters HR1 and HR2 change from a cold state to a preheated state.
1, rush current at the start of energization of HR2 (at the time of activation of heater circuit 6) can also be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. The power supply circuit according to the second embodiment shown in FIG. 2 differs from the power supply circuit according to the first embodiment shown in FIG. 1 in that an inrush current prevention circuit 25 is formed instead of the inrush current prevention circuit 15. And the heater circuit 26 instead of the heater circuit 6.

The inrush current prevention circuit 25 includes a relay RL
Is replaced with a switching contact Sy2 having a normally closed contact f and a normally opened contact g, and the normally opened contact g is inserted into one power supply line L. Further, a heater HR1 constituting the heater circuit 26 and a resistor R11 for preventing an inrush current are connected in series, and one of the power supply lines L
And the normally closed contact f of the switching contact Sy2. Then, the connection point h between the heater HR1 of the heater circuit 26 and the resistor R11 for preventing inrush current is connected to the energization control circuit 11
Is connected to the other power supply line N.

Next, the flow of the current from the time when the power switch 2 of the second embodiment is turned on to the time when the operation is shifted to the normal operation will be described. In the initial state, the relay RL is not operated, and the switching contact Sy2 closes the normally closed contact f and opens the normally open contact g as shown in the figure.

When the power switch 2 is turned on with the AC plug 1 attached to the outlet of the commercial power supply, the switches SW1 and SW2 of the power switch 2 are turned on, and the heater HR1 of the rush current prevention circuit 25 is turned on. Current flows through the rectifying / smoothing circuit 3 via the rush current preventing resistor R11.

If one of the AC power supply lines N and L is positive, the L → HR1 → R shown in FIG.
A current flows through a path of 11 → f → a → d → C1 → b → c → N, and charges the smoothing capacitor C1.

When the other power supply line N side is +, N
A current flows through the path of → c → d → C1 → b → a → f → R11 → HR1 → L, and charges the smoothing capacitor C1. In any case, the current is supplied to the heater HR1 having resistance.
And a resistor R11 for preventing an inrush current flows in series, so that there is sufficient resistance, so that an excessive current does not flow in the circuit and an inrush current is prevented from flowing.

In this state, after a while, the switching regulator 4 starts operating and the relay RL is activated in the same manner as in the first embodiment. However, when the relay RL is activated, the switching contact Sy2 is activated. The normally closed contact f is opened, and the normally opened contact g is closed.

In this way, the heater HR1 and the resistor R11 for preventing inrush current are disconnected from the power supply line to the rectifying / smoothing circuit 3, thereby preventing wasteful power consumption. Further, the heater HR1 is connected between the power supply lines L and N via the power supply control circuit 11, and the activation of the power supply control circuit 11 starts the operation as a normal heater.

According to this embodiment, since the heater and the inrush current prevention resistor are connected in series to the inrush current prevention circuit and used, the inrush current prevention resistor needs to have a small power rating. The cost can be reduced, and unnecessary power consumption is reduced. Further, when the power supply circuit is activated, a current flows through the heater HR1 of the heater circuit 26,
Since the heater HR1 changes from the cold state to the preheated state,
The resistance value becomes large, and the inrush current at the time of starting the energization to the heater HR1 by the activation of the energization control circuit 11 (at the time of activation of the heater circuit 26) can be reduced.

Next, a third embodiment of the present invention will be described with reference to FIG. The power supply circuit according to the third embodiment shown in FIG. 3 is different from the power supply circuit according to the second embodiment shown in FIG. 2 in that the inrush current preventing resistor R1 shown in FIG.
1, the rush current prevention circuit 35 is configured by directly connecting the heater HR1 of the heater circuit 36 between the one power supply line L and the normally closed contact f of the switching contact Sy2 of the relay RL. Then, the heater HR1 and the switching contact S
The connection point with the normally closed contact f at y2 is connected to the other power supply line N via the power supply control circuit 11.

The flow of current from the time when the power switch 2 of the third embodiment is turned on to the time when the power supply switch 2 shifts to the normal operation will be described.
In the initial state, the relay RL is not operated, and the switching contact Sy2 closes the normally closed contact f and opens the normally open contact g as shown in the figure. Therefore, when the power switch 2 is turned on while the AC plug 1 is attached to the outlet of the commercial power supply, the switches SW1 and SW2 of the power switch 2 are turned on, and the heater HR1 of the inrush current prevention circuit 35 is turned on. A current flows through the rectifying / smoothing circuit 3.

When one of the AC power supply lines N and L is positive, the signal L → HR1 → f shown in FIG.
A current flows through the path of → a → d → C1 → b → c → N, and the smoothing capacitor C1 is charged.

When the other power supply line N side is +, N
A current flows through the path of → c → d → C1 → b → a → f → HR1 → L, and the smoothing capacitor C1 is charged. In any case, since the current flows through the heater HR1 having resistance, there is sufficient resistance, so that an excessive current does not flow in the circuit and an inrush current is prevented from flowing.

In this state, after a while, the switching regulator 4 starts operating, the relay RL is activated, and the normally closed contact f of the switching contact Sy2 is opened.
The normally open contact g is closed as in the second embodiment. In this way, the heater HR1 is disconnected from the power supply line to the rectifying and smoothing circuit 3, thereby preventing wasteful power consumption. The heaters HR1 are connected to the power supply lines L and N via the power supply control circuit 11.
The operation as a normal heater is started by the activation of the energization control circuit 11.

According to this embodiment, since a heater is used in place of the inrush current prevention resistor of the inrush current prevention circuit, the inrush current prevention resistor becomes unnecessary, and the cost can be reduced accordingly. And wasteful power consumption is also reduced. Further, when the power supply circuit is started, a current flows through the heater HR1 of the heater circuit 36, and the heater HR1 changes from a cold state to a preheated state.
The inrush current at the start of energization of the heater HR1 by activation of the energization control circuit 11 (at the time of activation of the heater circuit 36) can also be reduced.

When the heater circuit has two heaters, the first embodiment may be employed. Further, even when only one heater is provided in the heater circuit, the third embodiment may be adopted if the heater has a sufficient resistance value and current rating. And the heater circuit has only one heater,
If the resistance value of the heater is not sufficient, the second embodiment may be adopted, and only the insufficiency resistance may be supplemented by the inrush current prevention resistor R11.

Each of the power supply circuits according to the first to third embodiments is a power supply circuit in which a switching regulator 4 for generating a high DC voltage is connected to the output side of the rectifying / smoothing circuit 3. Is a power supply circuit of an electrophotographic image forming apparatus that applies a DC high voltage applied to a charging charger, a transfer charger, and the like. In this case, the heater is a heater for heating the fixing device.

However, the present invention is not limited to this, and all the inrush current prevention circuits in a power supply circuit in which a capacitor input type rectifying and smoothing circuit and a heater circuit are provided in parallel to an AC power supply via a power switch are provided. Applicable.

[0049]

As described above, the inrush current prevention circuit in the power supply circuit according to the present invention is such that when the power supply circuit is started after the power switch is turned on, the heater of the heater circuit is entirely or partially provided with the resistance for preventing the inrush current. Therefore, a resistor for preventing an inrush current is not required, or at least a resistor having a small power rating can be used, so that cost reduction and unnecessary power consumption can be reduced. Further, current flows to the heater when the power supply circuit is started, and the heater changes from a cold state to a preheated state. Therefore, the resistance value increases, and the rush current at the time of starting the heater circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a power supply circuit including an inrush current prevention circuit according to the present invention.

FIG. 2 is a circuit diagram showing a power supply circuit including a rush current prevention circuit according to a second embodiment of the present invention;

FIG. 3 is a circuit diagram showing a third embodiment of a power supply circuit including an inrush current prevention circuit according to the present invention.

FIG. 4 is a circuit diagram showing an example of a power supply circuit including a conventional inrush current prevention circuit.

[Description of Signs] 1: AC plug 2: Power switch 3: Rectifying smoothing circuit 4: Switching regulator 6, 26, 36: Heater circuit 10: Control IC 11: Energization control circuit 12: Photocoupler circuit 15, 25, 35: Inrush current prevention circuit BR: Full-wave rectifier circuit (diode bridge) C1: Smoothing capacitor R2: Starting resistor Q: Switching element T: Transformer RL: Relay Sy1: Normally open contact Sy2: Switching contact HR1, HR2: Heater R11: Resistor for preventing inrush current L: One feed line N: The other feed line

Claims (5)

[Claims] 1. A power supply circuit in which a rectifying / smoothing circuit and a heater circuit are provided in parallel to an AC power supply via a power switch, wherein one power supply line between the power switch and the rectifying / smoothing circuit is provided. A normally open contact of a relay that operates when the smoothing capacitor of the rectifying / smoothing circuit is charged by a predetermined amount is inserted, and two heaters constituting the heater circuit are connected in series to be parallel to the normally open contact of the relay. And a connection point of the two heaters is connected to the other power supply line between the power switch and the rectifying / smoothing circuit via a conduction control circuit. 2. A power supply circuit in which a rectifying / smoothing circuit and a heater circuit are provided in parallel with an AC power supply via a power switch, wherein one power supply line between the power supply switch and the rectifying / smoothing circuit is provided. The normally open contact in the switching contact of the relay that operates when the smoothing capacitor of the rectifying smoothing circuit is charged by a predetermined amount is inserted, and the heater constituting the heater circuit and the rush current preventing resistor are connected in series. Connected between the one power supply line and the normally-closed contact of the switching contact of the relay, and connects a connection point between the heater and the resistor to the power switch and the rectifying / smoothing circuit via a conduction control circuit. A rush current prevention circuit connected to the other power supply line between the two. 3. A power supply circuit in which a rectifying / smoothing circuit and a heater circuit are provided in parallel to an AC power supply via a power switch, wherein one power supply line between the power switch and the rectifying / smoothing circuit is provided. The normally open contact of the switching contact of the relay that is activated when the smoothing capacitor of the rectifying and smoothing circuit is charged by a predetermined amount is inserted, and the heater constituting the heater circuit is connected to the one of the power supply line and the switching contact of the relay. Connected between the power supply switch and the rectifying / smoothing circuit via a conduction control circuit. Characteristic inrush current prevention circuit. 4. The inrush current prevention circuit in the power supply circuit according to claim 1, wherein the power supply circuit connects a switching regulator that generates a high DC voltage to an output side of the rectifying and smoothing circuit. Inrush current prevention circuit which is a power supply circuit. 5. The rush current prevention circuit according to claim 4, wherein said power supply circuit is a power supply circuit for an electrophotographic image forming apparatus, and said heater is a heater for heating a fixing device. circuit.