JP5915183B2 - Power circuit - Google Patents

Description

  The present invention relates to a power supply circuit.

  The following power supply circuit is described in Patent Document 1 below. The power supply circuit includes a rectifier circuit that rectifies an input AC voltage, a smoothing unit that smoothes the voltage from the rectifier circuit, and a threshold value that increases when the smoothed voltage increases and decreases when the smoothed voltage decreases. The threshold voltage generation unit that generates the voltage, the voltage from the rectifier circuit and the threshold voltage are compared, and when the voltage from the rectifier circuit is equal to or higher than the threshold voltage, the voltage from the rectifier circuit is not supplied to the output unit, When the voltage from the rectifier circuit is less than the threshold voltage, an output control unit that supplies the voltage from the rectifier circuit to the output unit, and an output unit that generates a DC voltage based on the voltage from the output control unit .

  When the AC voltage increases, the voltage value of the voltage from the rectifier circuit increases. Here, if the threshold voltage is constant, the period during which the voltage is supplied from the rectifier circuit to the output unit via the output control unit varies, the amount of charge supplied to the output unit changes, and the output voltage is a DC voltage. Fluctuates. However, the threshold voltage generated by the threshold voltage generation unit increases as the voltage obtained by smoothing the threshold voltage increases. Therefore, the amount of charge supplied to the output unit does not change, and the DC voltage that is the output voltage does not change. Similarly, when the AC voltage decreases, the threshold voltage generated by the threshold voltage generator decreases as the voltage obtained by smoothing the threshold voltage decreases. Therefore, the amount of charge supplied to the output unit does not change, and the DC voltage that is the output voltage does not change. As described above, according to the power supply circuit, a stable DC voltage can be output.

  However, since the power supply circuit of Patent Document 1 only compares the voltage from the rectifier circuit with the threshold voltage, the output voltage fluctuates when the current flowing from the capacitor of the output unit fluctuates. There is a problem of end. Even when the output capacitor (ie, load) is short-circuited to the ground potential, that is, when the capacitor charging voltage is 0 V (ground potential), the voltage from the rectifier circuit and the threshold voltage Since the current is supplied to the capacitor based only on the comparison result, the current cannot be sufficiently supplied to the output section, the protective fuse cannot be cut, and the protection cannot be activated. is there.

JP 2010-271554 A

  The present invention has been made to solve the above-described conventional problems, and a typical object of the present invention is to provide a power supply circuit capable of flowing a sufficient current to the output section even when the output section is short-circuited to the ground potential. It is to provide.

  A power supply circuit according to a preferred embodiment of the present invention is a power supply circuit that generates a DC voltage based on an input AC voltage, and rectifies the AC voltage, and increases as the voltage from the rectifier circuit increases. A threshold voltage generator that generates a threshold voltage that decreases when the voltage from the rectifier circuit decreases and that is fixed to a predetermined voltage when the voltage from the rectifier circuit is equal to or higher than a predetermined value; and an output of the power supply circuit When the output voltage of the power supply circuit is larger than the threshold voltage, the voltage from the rectifier circuit is not supplied to the output unit, and the output voltage from the power supply circuit is An output control unit that supplies a voltage from the rectifier circuit to the output unit, and a DC voltage that is an output voltage of the power supply circuit based on the voltage from the output control unit when the voltage is equal to or lower than the voltage. And a said output unit to be formed.

  According to the present embodiment, the output control unit compares the output voltage of the power supply circuit with the threshold voltage, and does not supply the voltage from the rectifier circuit to the output unit when the output voltage of the power supply circuit is larger than the threshold voltage. When the output voltage from the power supply circuit is equal to or lower than the threshold voltage, the voltage from the rectifier circuit is supplied to the output unit. Therefore, when the output unit is short-circuited, that is, when the output voltage of the power supply circuit becomes 0 V, the output control unit determines that the output voltage from the power supply circuit is below the threshold voltage for a long period. The current can continue to flow through the output section for a long period of time. Further, the output control unit compares the output voltage of the power supply circuit with the threshold voltage, and controls whether to supply the voltage from the rectifier circuit to the output unit according to the comparison result. The output voltage can be stabilized even when the current flowing through the capacitor fluctuates.

  In a preferred embodiment, the output control unit compares an output voltage of the power supply circuit with the threshold voltage, and changes to an on state or an off state, and an on state or an off state of the first transistor. And a second transistor that changes to an on state or an off state and switches supply or non-supply of the voltage from the rectifier circuit to the output unit, and the base of the first transistor includes An output voltage is supplied, and the threshold voltage is supplied to the emitter of the first transistor.

  In a preferred embodiment, the current flowing from the second transistor to the output unit is detected to change the second transistor to an off state, and the current flowing from the second transistor to the output unit is limited. And a third transistor.

  The third transistor determines the magnitude of the current flowing from the rectifier circuit to the output unit via the second transistor, and when it detects that the current is excessive, it changes the second transistor to the off state. To function. If a large current flows instantaneously, there are problems such as generation of radiation noise and an increase in power consumption. However, provision of the third transistor can prevent an excessively large current from flowing.

  It is possible to provide a power supply circuit capable of flowing a sufficient current to the output unit even when the output unit is short-circuited to the ground potential.

1 is a circuit diagram showing a power supply circuit according to a preferred embodiment of the present invention. It is a simulation result which shows operation | movement of the power supply circuit of this invention. It is a simulation result which shows operation | movement of the power supply circuit of this invention. It is a simulation result which shows operation | movement of the power supply circuit of this invention. It is a simulation result which shows operation | movement of the power supply circuit of this invention. FIG. 6 is a circuit diagram showing a power supply circuit according to another preferred embodiment of the present invention.

  Hereinafter, although preferable embodiment of this invention is described, this invention is not limited to these embodiment. FIG. 1 is a schematic circuit diagram showing a power supply circuit 1 according to a preferred embodiment of the present invention. The power supply circuit 1 generally includes a full-wave rectifier circuit D1, a threshold voltage generation unit 2, an output control unit 3, and an output unit 4.

  In the power supply circuit 1, the output control unit 3 compares the output voltage Vo of the power supply circuit 1 with the threshold voltage Vth generated by the threshold voltage generation unit 2, and when the output voltage Vo is larger than the threshold voltage Vth, The current based on the DC voltage Vd1 is not supplied to the output unit 4 (the DC voltage Vd1 is not supplied), and the current based on the DC voltage Vd1 is supplied to the output unit 4 when the DC voltage Vd1 is equal to or lower than the threshold voltage Vth ( DC voltage Vd1 is supplied).

  The threshold voltage Vth generated by the threshold voltage generator 2 increases as the DC voltage Vd1 increases, decreases as the DC voltage Vd1 decreases, and the DC voltage Vd1 from the rectifier circuit D1. Is fixed to a predetermined voltage when the value is equal to or higher than a predetermined value (that is, the threshold voltage Vth does not increase beyond the predetermined voltage).

  The full-wave rectifier circuit D1 has two input terminals connected to a secondary winding of a transformer (not shown), and full-wave rectifies the AC voltage input from the transformer to generate a DC voltage (full-wave rectified waveform) Vd1. And output. One output terminal of the full-wave rectifier circuit D1 is connected to the threshold voltage generator 2 and the output controller 3, and the other output terminal is connected to the ground potential. A fuse f is connected to one input terminal of the full-wave rectifier circuit D1.

  The threshold voltage generation unit 2 generates a threshold voltage Vth for determining whether or not the output control unit 3 supplies a current based on the DC voltage Vd1 from the full-wave rectifier circuit D1 to the output unit 4. The generated threshold voltage Vth is supplied to the emitter of the transistor Q1 of the output control unit 3. The threshold voltage Vth varies according to the voltage value of the DC voltage Vd1 from the full-wave rectifier circuit D1. That is, when the DC voltage from the full-wave rectifier circuit D1 increases, the threshold voltage Vth generated by the threshold voltage generator 2 also increases, and when the DC voltage from the full-wave rectifier circuit D1 decreases, the threshold voltage The threshold voltage Vth generated by the voltage generator 2 also decreases. When the DC voltage from full-wave rectifier circuit D1 is equal to or higher than a predetermined voltage, threshold voltage Vth is fixed without increasing beyond the predetermined voltage.

  The threshold voltage generation unit 2 includes a Zener diode D2 that is a constant voltage generation unit, and a resistor R1. One end of the resistor R1 is connected to the output of the full-wave rectifier circuit D1, and the other end is connected to the emitter of the transistor Q1 and the cathode of the Zener diode D2. The anode of the Zener diode D2 is connected to the ground potential. The threshold voltage Vth is a voltage obtained by subtracting the voltage across the resistor R1 from the DC voltage Vd1 output from the full-wave rectifier circuit D1, but does not increase beyond the Zener voltage of the Zener diode D2. Therefore, it increases or decreases between the Zener voltage of the Zener diode D2 and 0 V as the DC voltage Vd1 from the full-wave rectifier circuit D1 increases or decreases.

  The output controller 3 compares the output voltage Vo of the power supply circuit 1 with the threshold voltage Vth generated by the threshold voltage generator 2, and when the output voltage Vo is larger than the threshold voltage Vth, the current based on the DC voltage Vd1 Is not supplied to the capacitor C2 of the output unit 4 (DC voltage Vd1 is not supplied to the capacitor C2), and when the output voltage Vo is equal to or lower than the threshold voltage Vth, a current based on the DC voltage Vd1 is supplied to the capacitor C2 of the output unit 4. (Supply DC voltage Vd1 to capacitor C2).

  The output control unit 3 compares the output voltage Vo and the threshold voltage Vth, and outputs / outputs the comparison result, and supply / non-supply of the DC voltage Vd1 to the capacitor C2 according to the comparison result from the transistor Q1. And a transistor Q3 for switching between. Output control unit 3 further includes a transistor Q2, resistors R2 to R5, and a capacitor C1.

  The transistor Q1 has a base connected to one end of the capacitor C2 of the output unit 4 via the resistor R4 to be supplied with an output voltage Vo, and an emitter connected to a connection point between the resistor R1 and the cathode of the Zener diode D2 to generate a threshold voltage. Vth is supplied, and the collector is connected to the ground potential via the resistor R2. The transistor Q1 is turned off when the output voltage Vo is larger than the threshold voltage Vth, and turned on when the output voltage Vo is equal to or lower than the threshold voltage Vth. Actually, since the ON state or the OFF state of the transistor Q1 is determined in consideration of the conduction start voltage of the transistor Q1 of 0.6V and the voltage across the resistor R4, the threshold voltage generated by the threshold voltage generator 2 is determined. A voltage obtained by adding the conduction start voltage 0.6V of the transistor Q1 and the voltage across the resistor R4 to the voltage Vth can be said to be a broad threshold voltage.

  The base of the transistor Q2 is connected to the collector of the transistor Q1 via the resistor R3, is connected to the ground potential via the resistor R2, and is connected to the ground potential via the capacitor C1, and the collector is connected via the resistor R5. The emitter of the transistor Q3 is connected to the ground potential.

  The base of the transistor Q3 is connected to the collector of the transistor Q2 via the resistor R5, the emitter is connected to one output terminal of the full-wave rectifier circuit D1, and the collector is connected to the anode of the diode D3 of the output unit 4. Yes. The transistor Q3 is turned on when the transistor Q1 is turned on, passes a current based on the DC voltage Vd1 from the full-wave rectifier circuit D1 to the capacitor C2 of the output unit 4, and is turned off when the transistor Q1 is turned off. Thus, the current based on the DC voltage Vd1 from the full-wave rectifier circuit D1 is not passed through the capacitor C2 of the output unit 4.

  The output unit 4 generates a smoothed DC voltage that is the output voltage Vo of the power supply circuit 1 by charging the capacitor C2 with a current supplied from the full-wave rectifier circuit D1 via the output control unit 3. The output unit 4 includes a diode D3 and a capacitor C2. The diode D3 has an anode connected to the collector of the transistor Q3 and a cathode connected to one end of the capacitor C2 and one end of the load RL. Capacitor C2 has one end connected to the cathode of diode D3, resistor R4, and load RL, and the other end connected to the ground potential.

  The operation of the power supply circuit 1 having the above configuration will be described. FIG. 2 shows simulation results obtained by measuring the input AC voltage to the full-wave rectifier circuit D1, the output voltage Vo, and the current flowing from the transistor Q3 to the capacitor C2. Hereinafter, description will be made with reference to FIGS. 1 and 2.

  The full-wave rectifier circuit D1 performs full-wave rectification on an AC voltage input from a transformer (not shown), generates a DC voltage Vd1, and supplies the DC voltage Vd1 to the threshold voltage generator 2 and the output controller 3. The threshold voltage generator 2 generates a threshold voltage Vth based on the DC voltage Vd1 from the full-wave rectifier circuit D1, and supplies it to the emitter of the transistor Q1. An output voltage Vo that is a charging voltage of the capacitor C2 is supplied to the base of the transistor Q1 via the resistor R4. The transistor Q1 compares the magnitude relationship between the output voltage Vo and the threshold voltage Vth.

  In the period T1, since the amplitude value of the input AC voltage is small, the value of the threshold voltage Vth generated from the input AC voltage is also small. Accordingly, the output voltage Vo (actually, the conduction start voltage of the transistor Q1 and the voltage across the resistor R4 are considered, the same applies hereinafter) is greater than the threshold voltage Vth, and the transistor Q1 is turned off. When the transistor Q1 is turned on, the transistor Q2 is turned off because the base is connected to the ground potential. Therefore, the transistor Q3 is turned off because the base is released from the ground potential by turning off the transistor Q2.

  Therefore, when the transistor Q3 is turned off, a current based on the DC voltage Vd1 from the full-wave rectifier circuit D1 does not flow to the capacitor C2. As a result, during the period T1 in which the output voltage Vo is greater than the threshold voltage Vth, the capacitor C2 is not charged, and the charging voltage Vo of the capacitor C2 is consumed by the load RL and gradually decreases.

  In the period T2, since the amplitude value of the input AC voltage is large, the threshold voltage Vth generated from the input AC voltage is also large. However, when the input AC voltage is equal to or higher than a certain value, the threshold voltage Vth does not exceed the predetermined voltage but is fixed to the predetermined voltage. On the other hand, the output voltage Vo decreases due to the operation in the period T1. Accordingly, the output voltage Vo becomes lower than the threshold voltage Vth, and the transistor Q1 is turned on. When the transistor Q1 is turned on, the transistor Q2 is turned on because the base is connected to the emitter of the transistor Q1 and the threshold voltage Vth is supplied. Accordingly, when the transistor Q2 is turned on, the transistor Q3 is turned on because the base is connected to the ground potential.

  Accordingly, when the transistor Q3 is turned on, a current based on the DC voltage Vd1 from the full-wave rectifier circuit D1 flows to the capacitor C2 via the transistor Q3 and the diode D3, and the capacitor C2 is charged, and the output voltage Vo A certain DC voltage increases little by little.

  In the period T3, the input AC voltage is higher than that in the period T2, but the threshold voltage Vth is fixed to the predetermined voltage as described above. On the other hand, the output voltage Vo is increased by the operation in the period T2. Therefore, the output voltage Vo is larger than the threshold voltage Vth, and the transistor Q1 is turned off. When the transistor Q1 is turned off, the transistor Q2 is turned off because the base is connected to the ground potential. Accordingly, when the transistor Q2 is turned off, the transistor Q3 is released from the ground potential, and thus is turned off.

  Therefore, when the transistor Q3 is turned off, a current based on the DC voltage Vd1 from the full-wave rectifier circuit D1 does not flow to the capacitor C2. As a result, during the period T3 in which the output voltage Vo is greater than the threshold voltage Vth, the capacitor C2 is not charged, and the charging voltage Vo of the capacitor C2 is consumed by the load RL and gradually decreases.

  In the period T4, the input AC voltage decreases from the period T3. Also in the period T4, the output voltage Vo is higher than the threshold voltage Vth, and the transistor Q1 is turned off. When the transistor Q1 is turned off, the transistor Q2 is turned off because the base is connected to the ground potential. Accordingly, when the transistor Q2 is turned off, the transistor Q3 is released from the ground potential, and thus is turned off.

  Therefore, when the transistor Q3 is turned off, a current based on the DC voltage Vd1 from the full-wave rectifier circuit D1 does not flow to the capacitor C2. As a result, during the period T4 in which the output voltage Vo is larger than the threshold voltage Vth, the capacitor C2 is not charged, and the charging voltage Vo of the capacitor C2 is consumed by the load RL and gradually decreases.

  FIG. 3 shows simulation results obtained by measuring the input AC voltage to the full-wave rectifier circuit D1, the output voltage Vo, and the current flowing from the transistor Q3 to the capacitor C2 when the input AC voltage fluctuates. Va corresponds to Ia, Vb corresponds to Ib, and Vc corresponds to Ic. Since the output voltage Vo is compared with the threshold voltage Vth and the transistor Q3 is on / off controlled, it can be seen that the output voltage Vo can be held constant even if the input AC voltage fluctuates.

  FIG. 4 shows a simulation result of measuring the input AC voltage to the full-wave rectifier circuit D1, the output voltage Vo, and the current flowing from the transistor Q3 to the capacitor C2 when the current flowing from the capacitor C2 to the load RL fluctuates. It is. When the current flowing from the capacitor C2 to the load RL fluctuates, the output voltage Vo tries to fluctuate. However, since the transistor Q3 is controlled on and off by comparing the output voltage Vo and the threshold voltage Vth, the output voltage Vo Variations can be suppressed. That is, when the current flowing from the capacitor C2 to the load RL increases, if the voltage Vo of the capacitor C2 is decreased, the period during which the transistor Q3 is turned on increases, and a large amount of current flows from the transistor Q3 to the capacitor C2. A decrease in the voltage Vo of the capacitor C2 is suppressed. As a result, the output voltage Vo can be kept constant.

  FIG. 5 shows a full-wave rectifier circuit when one end of the capacitor C2 (one end of the load RL) is short-circuited and connected to the ground potential, that is, when the charging voltage of the capacitor C2, which is the output voltage Vo, becomes 0V. It is the simulation result which measured the input alternating voltage to D1, and the electric current which flows into the capacitor | condenser C2 from the transistor Q3. In this case, since the output voltage Vo is 0 V, the output voltage Vo is always equal to the threshold voltage regardless of the magnitude of the threshold voltage Vth, except for a few periods T31 and T33 in which the threshold voltage Vth is around 0 V. Vth or less, and the transistor Q1 is turned on. Accordingly, the transistor Q3 is turned on, and a current flows from the transistor Q3 to the capacitor C2 over a long period of the period T32. Therefore, when the load RL is short-circuited, the fuse f can be blown and the protect operation can be activated.

  FIG. 6 is a circuit diagram showing a power supply circuit 11 according to another embodiment of the present invention. The same parts as those in FIG. Power supply circuit 11 further includes transistors Q4 and Q5 and resistors R6 and R7. In particular, by including the transistor Q5 and the resistor R6, it is possible to prevent the current flowing through the capacitor C2 via the transistor Q3 from becoming too large. The transistor Q4 is a transistor that transmits the on / off states of the transistors Q2 and Q5 to the transistor Q3.

  The transistor Q5 has a base connected to one end of the resistor R6 and the emitter of the transistor Q3, a collector connected to a connection point between the base of the transistor Q4 and the resistor R5, an emitter connected to the other end of the resistor R6, and a full-wave rectifier circuit. Connected to the output of D1.

  The transistor Q5 is supplied with a voltage obtained by subtracting a voltage generated at both ends of the resistor R6 from the DC voltage Vd1 output from the full-wave rectifier circuit D1 due to the current flowing to the capacitor C2 via the transistor Q3. Is supplied with the DC voltage Vd1 from the full-wave rectifier circuit D1. Accordingly, when the current flowing through the capacitor C2 through the transistor Q3 becomes excessive, the voltage at the base of the transistor Q5 becomes smaller than the voltage at the conduction than the voltage at the emitter, and the transistor Q5 is turned on. When the transistor Q5 is turned on, the transistor Q4 is turned off, and as a result, the transistor Q3 is turned off. Therefore, the current flowing through the capacitor C2 through the transistor Q3 is cut off, and it is possible to prevent the current flowing through the capacitor C2 through the transistor Q3 from becoming too large. Actually, before the transistor Q5 is completely turned on, the current flowing to the capacitor C2 through the transistor Q3 is limited so that the condition for turning on the transistor Q5 is not satisfied, and the transistor Q5 is turned on. Return immediately.

  As described above, by limiting the current flowing through the capacitor C2 via the transistor Q3 so as not to increase to a predetermined value or more, radiation noise can be prevented and power consumption can be prevented from increasing. .

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment. The polarity of each transistor is not limited to the above embodiment.

  The present invention can be suitably employed in a power supply circuit of an audio device such as an amplifier.

DESCRIPTION OF SYMBOLS 1 Power supply circuit 2 Threshold voltage generation part 3 Output control part 4 Output part

Claims (2)

A power supply circuit that generates a DC voltage based on an input AC voltage,
A rectifier circuit for rectifying the AC voltage;
A threshold value that increases when the voltage from the rectifier circuit increases, decreases when the voltage from the rectifier circuit decreases, and generates a threshold voltage that is fixed to a predetermined voltage when the voltage from the rectifier circuit is equal to or higher than a predetermined value. A voltage generator;
When the output voltage of the power supply circuit is compared with the threshold voltage, and the output voltage of the power supply circuit is greater than the threshold voltage, the voltage from the rectifier circuit is not supplied to the output unit, An output control unit that supplies a voltage from the rectifier circuit to the output unit when an output voltage is equal to or lower than the threshold voltage;
Based on the voltage from the output control unit, the output unit that generates a DC voltage that is an output voltage of the power supply circuit ,
The output control unit compares the output voltage of the power supply circuit with the threshold voltage, the first transistor changing to an on state or an off state, and an on state in response to the on state or the off state of the first transistor Or a second transistor that changes to an off state and switches between supply and non-supply of the voltage from the rectifier circuit to the output unit,
Wherein the first transistor based is supplied the output voltage of the power supply circuit, the emitter of the first transistor the threshold voltage Ru is supplied, the power supply circuit. A third transistor for detecting an excessive current flowing from the second transistor to the output unit, changing the second transistor to an off state, and limiting a current flowing from the second transistor to the output unit; The power supply circuit according to claim 1 , comprising: