JP2002262562A - Power control device and structure thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power control device that supplies a stable DC output voltage. SOLUTION: A switching power supply (96) receives an AC voltage and converts it into a controlled DC voltage. The switching power supply (96) includes a VCC limiter and limits an operating voltage at a power supply terminal (10) in an integrated regulator circuit (118). If the operating voltage at the power supply terminal is increased, a pair of differential transistors (22 and 24) supply differential currents to current mirror structures of transistors (26 and 30), and increases the current of a driving transistor (36) to a value obtained by multiplying the current of a reference transistor (26) by a factor of n. As the result of the increase in the current which passes through the driving transistor (36), the operating voltage at the power supply terminal (10) is increased, and the level of the operating voltage is thereby drawn back to a desired level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates generally to electronic circuits, and more particularly, to a switching power supply that converts an AC signal to a regulated DC signal.

[0002]

BACKGROUND OF THE INVENTION Most, if not all, electronic devices require an appropriate level of DC voltage for proper operation.
The DC voltage is typically derived by connecting the power supply to an AC power supply, such as a wall socket. The AC voltage available at the wall socket is converted to a DC bulk voltage by a full-wave rectifier diode bridge. The DC bulk voltage is further converted to a regulated DC output voltage by a switching power supply.

[0003] Switching power supplies use transformers or shape-dependent inductors as energy conversion elements. For example, a flyback type power supply has a power switching transistor coupled to one side of a main winding of a transformer. The power switching transistor turns on and off in accordance with the regulations of the regulator, alternately stores energy in the transformer magnetic field, and transfers the stored energy to the secondary winding. The secondary winding of the transformer produces an output voltage as a function of energy transfer across a shunt capacitor coupled across the secondary winding. The voltage across the capacitor gives the DC output voltage of the switching power supply.

[0004] The DC output voltage increases and decreases depending on the applied load. Increasing the load will decrease the DC output voltage, and decreasing the load will increase the DC output voltage. The DC output voltage or a value representing it is returned to the regulator circuit, allowing the supply of switching power to compensate for load changes. As the load increases, DC
The lower output voltage causes the power transistor to stay on longer for longer to store more energy in the magnetic field. Additional energy is transferred to the secondary winding while the power transistor is off, supplying the increased load to re-establish the DC output voltage. As the load decreases, the DC output voltage increases, which leaves the regulator on for a shorter time to store less energy in the magnetic field. During the off time of the power transistor,
Due to the reduced energy transfer to the secondary winding, the power supply is regulated to the reduced load and returns the DC output voltage to its steady state value.

[0005]

One prior art switching power supply has an integrated regulator circuit that includes a combined feedback and power supply for a single input pin. Integrated regulator circuits have isolation circuits in the chip to separate feedback and power signals. By combining the feedback and power supply signals on a single pin, the integrated regulator can require fewer pins. However, in many cases, there is a sufficient number of available pins, which eliminates the need to combine feedback and power signals on a single pin. The design of the integrated regulator circuit is simplified by having the feedback and power delivered to separate pins. In applications where feedback and power are conveyed on a single pin, the isolation circuit introduces unnecessary complexity in the integrated circuit without the attendant needs and advantages.

[0006] Thus, there is a need for an integrated regulator circuit that completely separates the operating voltage and feedback input pins and does not require complex isolation circuits.
The circuit also limits excessive operating voltage,
Thereby, a low voltage circuit can be used in the integrated regulator circuit.

[0007]

FIG. 1 shows a conventional switching power supply 50 which receives an AC line voltage and regulates it with a regulated D.
Convert to C operating voltage. Specifically, the AC line voltage is converted by the full-wave rectifier diode bridge 52 to a DC bulk voltage. Capacitor 54 filters the DC bulk voltage, and the main winding of transformer 58 receives the DC bulk voltage. Power transistor 90 converts the induced current to transformer 58
To control the amount of energy stored in the transformer's magnetic field. Power transistor 90 is flyback
When operating in the mode configuration, the induced current flows through the main winding and stores energy in the magnetic field of transformer 58. When power transistor 90 is off, the energy stored in the magnetic field is transferred to the secondary winding and capacitor 62
Coupled across the secondary winding to provide a DC output voltage V _OUT .

In the normal mode of operation, current flows through resistor 78 and zener diode 80. The diode 76 and the photodetector transistor 82 operate cooperatively and optically couple to feed back information from the capacitor 62 to the coupled feedback and power supply 86 of the regulator circuit 70. The DC output voltage (V _OUT ) is typically regulated in advance according to the output load.
It operates either slightly above or below the ion threshold. If the output load is relatively large and V _OUT falls below the regulation threshold, the voltage across resistor 78 will cause photodiode 76 to become less forward biased, thereby rendering transistor 82 less conductive and providing less feedback. Resulting in the application of a signal. As V _OUT increases above the regulation threshold, photodiode 76 becomes more forward biased and transistor 82 becomes more conductive and the feedback signal becomes stronger.

The feedback information resulting from the fluctuation of the DC output voltage is supplied to the transistor 82 by the diode 76.
The power supply terminal 8 of the regulator circuit 70
6 is combined. Thus, the combined feedback and power signal is applied to power terminal 86. The regulator circuit 70 uses an internal separation circuit to separate a power supply that supplies power to the integrated circuit from a feedback signal that controls pulse width modulation and generates a gate drive signal to the power transistor 90. Power transistor 90 controls the amount of energy sent through transformer 58 and turns it on and off with the required duty cycle to regulate V _OUT .

FIG. 2 shows a preferred embodiment of the switching power supply 96. Specifically, the switching power supply 96
Receives C-line voltage and converts it to regulated DC operating voltage. The AC line voltage is converted to a DC bulk voltage by a full-wave rectifier diode bridge 98. Capacitor 100
Filters the DC bulk voltage, and the DC bulk voltage is received by the main winding of the transformer 104. Power transistor 44
Conducts induced current through the main winding of transformer 104, controls the amount of energy stored in the transformer's magnetic field, and operates in a regulated cycle controlled by switching regulator circuit 18. When power transistor 44 operates in a flyback mode configuration, the induced current flows through the main winding and stores energy in the magnetic field of transformer 104. When the power transistor 44 is non-conductive, the energy stored in the magnetic field is transferred to the secondary winding, where a capacitor 108 coupled across the secondary winding produces a DC output voltage (V _OUT ). The diode 106 has a current of 2
Prevent backflow to the next winding.

In response to V _OUT variations, feedback information is combined and returned by feedback circuit 116 to regulation circuit 118. That information is returned to the base of transistor 14 by an optical light emitting diode (LED) 120 and received on feedback terminal 12 of regulator circuit 118. Feedback terminal 12 is connected to the emitter of transistor 14. The received feedback information controls pulse width modulation in switching regulator 18 and generates a gate drive signal to power transistor 44. Power transistor 44 controls the amount of energy in transformer 104 and V
Turn it on and off with the required duty cycle to regulate _OUT . A specific form of the power transistor 44 is a high-voltage J in which a low-voltage MOSFET is connected in series.
FET. The gate of the low voltage MOSFET receives the drive signal and the drain of the high voltage JFET is connected to the transformer 104.
Connected to.

The power supply terminal 10 receives power supply from the auxiliary winding 111. The diode 110, the resistor 112, and the capacitor 114 are connected to the auxiliary winding 111. Power supply terminal 10 is connected to the collector of transistor 14.

In normal operating conditions, current flows through resistor 122 and zener diode 124. LE
D120 and photodetector transistor 14 operate to return information from capacitor 108 to feedback terminal 12 of regulator circuit 118 in response to _VOUT fluctuations. When an LED is forward biased, the current flowing through the LED then produces an amount of photons that is proportional to the current flow. The photon is transistor 1
4 to receive light and make it conductive. Transistor 14 conducts current from its collector to its emitter. If LED 120 is not forward biased, LED
No photons are emitted from 120, rendering transistor 14 non-conductive.

The feedback circuit 116 typically comprises an LED 120 having an anode and a cathode, a resistor 122 having two terminals, a diode 124 having an anode and a cathode, and a light detecting transistor having two conduction terminals and one control terminal. 14. The anode of LED 120 is the first of capacitor 108
Coupled to the terminals, the cathode of LED 120 is connected to the cathode of diode 124, and the anode of diode 124 is coupled to receive ground potential. Resistance 122
Has a first terminal coupled to the anode of LED 120 and a second terminal coupled to the cathode of the LED. The drain of the transistor 14 is connected to the power supply terminal 1 of the regulator circuit 118.
Connected to 0. The source of transistor 14 is connected to feedback terminal 12 of regulator circuit 118, and the control terminal of transistor 14 is coupled to receive feedback information from LED 120. The power terminal 10 indicates an external pin that receives power. The feedback terminal 12 is an external pin that receives feedback information.

The regulator circuit 118 comprises the following. The power supply terminal 10 of the regulator circuit 118
It is coupled to the V _CC limiter 16 and regulates the operating voltage at the power terminal 10. The start-up circuit 17 is coupled to the power supply terminal 10 and starts the circuit during start or restart. Startup circuit 17 is implemented as US Pat. No. 5,477,175, which is incorporated herein by reference. A high voltage terminal (HV) is coupled to the drain of power transistor 44 and couples a high voltage on the main winding of transformer 104. HV terminal is a regulator circuit 118
External pins. Switching regulator circuit 1
8 is a feedback terminal 1 of the regulator circuit 118
2 to provide a drive signal to the power transistor 44. The switching regulator circuit 18 includes an oscillator 38, a comparator 40, a resistor 39, and a latch drive circuit 42. Oscillator 38 generates an output signal. Comparator 40 is coupled to receive the output signal of oscillator 38 and is coupled to receive the feedback signal on feedback terminal 12. Latch drive circuit 42 receives the output from comparator 40 and provides a drive signal to power transistor 44 as an output. Power transistor 44 has a drain coupled to HV of regulator circuit 118, a source coupled to ground potential 28, and a gate coupled to receive an output drive signal from switching regulator circuit 18. Resistor 39 has a first terminal coupled to receive the feedback signal on feedback terminal 12, and a second terminal coupled to ground potential 28. Regulator circuit 118 is implemented as an integrated circuit using a conventional, typically high voltage integrated circuit manufacturing process.

The DC output voltage V _OUT typically operates around a predetermined regulation threshold depending on the output load. The regulation threshold is set by the voltage obtained by adding the voltage across the Zener diode 124 to the voltage across the LED at the time of forward bias. If the output load is relatively large enough to cause V _OUT to fall below the regulation threshold, the voltage across resistor 122 will be L
ED 120 becomes less strongly biased in the forward direction, causing transistor 14 to become less conductive (less feedback). Increasing V _OUT above the regulation threshold will cause LED 120 to become more forward biased. The current is LED 120
And produces a quantity of photons proportional to the current.
Photons applied to the base of transistor 14 make it sufficiently conductive to cause a change in the current flowing through transistor 14. A change in the flow of current in transistor 14 _creates a voltage drop across resistor 39, denoted as V _FB . The voltage V _FB appears at a first terminal of the comparator 40, and a signal from the oscillator 38 is provided to a second terminal of the comparator 40. These two signals are applied to the input of comparator 40 and provide an output that controls the on-time of power transistor 44. Duty for comparator 40
The change in cycle causes a change in the on-time of the power transistor 44, providing the necessary change in V _OUT for regulation, resulting in a change in energy transfer to the secondary winding. If V _OUT is greater than the regulation threshold and a feedback signal is present, then the feedback loop will provide a higher voltage at feedback terminal 12 and switching regulator circuit 18 will reduce the gate drive signal to power transistor 44 and the duty cycle. Let it. As described above, V _OUT is maintained at the regulation threshold. By reducing the gate drive signal and duty cycle,
The average amount of time that power transistor 44 is conducting is reduced. Thus, by holding power transistor 44 off for a longer period of time, less additional energy is stored in the magnetic field of transformer 104. as a result,
Less energy is transferred to the secondary winding, thereby lowering V _OUT . Thus, switching regulator circuit 18 provides a gate drive signal to the gate of power transistor 44 in response to the feedback signal, turning the power transistor on and off as needed to regulate V _OUT .

FIG. 3 shows a V _CC limiter 16 for limiting the supply of the operating voltage at the power supply terminal 10. The feedback signal is received at feedback terminal 12 and another supply of operating voltage is applied to power supply terminal 10 of regulator circuit 118.
Power is received at. The supply of the operating voltage is distributed to the integrated circuit from the additional winding which receives the voltage fluctuation. Thus, the power supply terminal 10 requires a voltage limit.

V _CC limiter 16 is typically 1
0 μA constant current I ₂₀ is applied to a pair of differential transistors 22 and 2.
4 Transistor 22 is a p-type MOSFET
A transistor having a gate receiving the source and reference voltage to provide a drain, a difference current I ₁ to receive a portion of the constant current I _20. The reference voltage (V _ref ) typically operates at 1.25 volts. Transistor 24 is a p-type MOSFET transistor that has a drain coupled to receive the remainder of constant current I ₂₀ , a source providing difference current I ₂ , and resistors 32 and 34 and an operating voltage from power supply terminal 10. And a gate for receiving a voltage level divided by a resistor network. Resistor 32 has a terminal coupled to power supply terminal 10, and a terminal coupled to the gate of transistor 24. Resistor 34 includes a terminal coupled to the gate of transistor 24, and power supply terminal 2
And a terminal coupled to the terminal 8. Transistor pair 2
Reference numerals 6 and 30 constitute a current mirror shape. Transistor 2
6 is set to operate with a diode connection having a drain coupled to receive the difference current I ₁ from transistor 22, a source coupled to power supply terminal 28, and a gate connected to the drain. Transistor 30
Has a drain coupled to receive the difference current I ₂ from transistor 24, a source coupled to power supply terminal 28, and a gate connected to the gate of transistor 26. The current mirror configuration supplies the transistor 36 with a voltage to generate current and keeps the operating voltage variation at the power supply terminal 10 reduced. Transistor 36 has a drain coupled to receive the operating voltage at power supply terminal 10, a source coupled to power supply terminal 28, and a gate connected to the gate of transistor 26.

In a typical operation, if the operating voltage at the power supply terminal 10 exceeds a certain level, the voltage at the gate of the transistor 24 will also be proportional to the level based on the voltage dividing network formed by the resistors 32, To increase. The current mirror configuration supplies a voltage to the gate of transistor 36,
N times the current value in the transistor 26
Increase the conduction current. A typical value for n is 500. The increased conduction current through transistor 36 cancels the increased operating voltage at power supply terminal 10, thereby returning the operating voltage level to the desired level. If the operating voltage at power supply terminal 10 falls below a certain level, the voltage at the gate of transistor 24 will also
It decreases in proportion to the level based on the voltage division network formed by the circuits 2 and 34. The current mirror configuration supplies a voltage to the gate of transistor 36, reducing the conduction current in transistor 36 to n times the current in transistor 26. The reduced conduction current through transistor 36 cancels out the reduced operating voltage at power supply terminal 10, thereby returning the operating voltage level to the desired level.

In summary, the present invention shows a switching power supply 96 for use in power supply applications. Switching regulator circuit 18 receives the feedback signal in response to the V _OUT variation. The feedback signal is received at feedback terminal 12 of integrated regulator circuit 118, and a gate drive signal is applied to power transistor 44.
To supply. Power transistor 44 conducts induced current through the main winding of transformer 104 in response to the gate drive signal to reduce V _OUT fluctuations of switching power supply 96.

V _CC limiter 16 receives the operating voltage at power supply terminal 10 of integrated regulator circuit 118. Operating voltages typically have unwanted voltage fluctuations from the power supply and require voltage limiting. The V _CC limiter 16 as used provides a stable operating voltage and allows the integrated regulator circuit to have separate pins for feedback and operating voltage. In contrast to the prior art, embodiments do not require many additional circuits in the integrated regulator circuit and separate the feedback signal from the voltage signal. Further, by having separate feedback and operating pins, an external resistor can be used in parallel with resistor 39 to program the feedback.

As mentioned above, embodiments provide a more cost effective solution by reducing the complexity of the regulator circuit and reducing the size of the die, and, if desired, provide an optocoupler and additional winding configuration. Provide choices to use.

[Brief description of the drawings]

FIG. 1 shows a schematic diagram of a conventional power supply.

FIG. 2 shows a schematic diagram of a switching power supply including a V _CC limiter.

FIG. 3 shows a schematic diagram of the V _CC limiter included in FIG.

[Explanation of symbols]

_DESCRIPTION OF SYMBOLS 10 Power supply terminal 12 Feedback terminal 14 Transistor 16 V _CC limiter 17 Start-up circuit 18 Switching regulator circuit 38 Oscillator 42 Latch drive circuit 44 Power transistor 96 Switching power supply 104 Transformer 116 Feedback circuit 120 LED 124 Zener diode

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[Procedure amendment]

[Submission date] May 11, 2001 (2001.5.1
1)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 3

FIG. 2

Continued on the front page (72) Inventor Wilson Dee Pais United States of America Arizona Tempe East Tulane Drive 1845 (72) Inventor Christopher Gas United States of America Arizona Tempe West Minton Drive 564 F-term (reference) 5H730 AS01 BB43 BB57 CC01 DD04 DD12 DD26 EE02 EE07 EE73 FD01 FF19 FG05 VV03 VV06

Claims (3)

[Claims] A first power supply terminal for receiving an operating voltage for the regulator circuit; a feedback terminal; a first conduction terminal coupled to the first power supply terminal; a second conduction terminal coupled to the feedback terminal. A first transistor having a control terminal coupled to receive a feedback signal; and a V _CC limiter coupled to the first power supply terminal for regulating the operating voltage; and providing a regulator output signal. And a switching regulator circuit coupled to the feedback terminal. 2. A regulator circuit for regulating a power supply, the regulator circuit being coupled to a feedback terminal at a first pin of the regulator circuit for receiving a feedback signal for controlling the switching regulator circuit and providing a regulator output signal. A switching regulator circuit; and a V _CC limiter coupled to a first power supply terminal at a second pin of the regulator for receiving an operating voltage,
The V _CC limiter regulator circuit, characterized in that they are composed of regulating the operating voltage of a portion of the first power supply terminal and the switching regulator circuit, and V _CC limiter. 3. A method for regulating a power supply for an integrated circuit, comprising: receiving a feedback signal at a feedback terminal of the integrated circuit; controlling the integrated circuit with the feedback signal to provide a regulator output signal. And receiving an operating voltage at a first power supply terminal of the integrated circuit; and limiting the operating voltage at a portion of the first power supply terminal and the integrated circuit. And how.