JPH05260742A - Insulation type power circuit - Google Patents

Abstract

PURPOSE:To stabilize an output voltage precisely by executing feedback of the output voltage by a switching operation by a pulse transformer without using a photocoupler which has the possibility of deterioration in characteristics. CONSTITUTION:The primary winding of a pulse transformer 10 and a first transistor 11 are connected in series between output terminals and the base of a second transistor inserted between the base and the emitter of the first transistor is connected onto the anode side of a circulation diode 6 through a second base resistor 14. A voltage on the secondary side of the pulse transformer is subjected to DC conversion by a signal rectifying diode 16 and a signal smoothing capacitor 17 and then a forward voltage drop of a signal rectifying diode 21 is corrected by a diode 21 for compensation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulated power supply circuit for space, for example, and its output voltage is fed back to a control circuit on a primary side using a pulse transformer to stabilize the output voltage.

[0002]

2. Description of the Related Art As an insulated power supply circuit, the one shown in FIG. 4 is conventionally known. In the figure, 1 is a switching element, 2 is a power transformer, 3 is a drive circuit, 4 is a control circuit, 5 is a rectifying diode, 6 is a freewheeling diode, 7 is a first smoothing choke coil, 8 is a second smoothing choke coil, Reference numeral 9 is a smoothing capacitor, 23 is a shunt regulator, 24 and 25 are resistors for dividing an output voltage, 26 is a current limiting resistor, and 27 is a photocoupler.

Next, the operation will be described. When a DC voltage is switched by the switching element 1, electric power is transmitted to the secondary side through the power transformer 2, and when the switching element 1 is conducting, it flows through the rectifying diode 5 and when the switching element 1 is not conducting, it flows through the freewheeling diode 6. A current continuously flows through the first choke coil 7 and the second choke coil 8, is smoothed into a DC voltage again by the smoothing capacitor 9, and is supplied to the load. This output voltage is controlled by the conduction ratio of the switching element. This control is compared with an internal reference voltage by a shunt regulator 23 that detects the voltage at the dividing points of the resistors 24 and 25 that divide the output voltage, and the current limit is established. A current flows through the light emitting diode of the photocoupler 27 through the resistor 26. Then, a DC voltage having a level corresponding to the output voltage is detected on the light receiving transistor side of the photocoupler 27, and the control circuit 4 performs control at this voltage level, and the switching element 1 via the drive circuit 3.
To drive. This operation stabilizes the output voltage.

[0004]

The conventional isolated power supply circuit is constructed as described above, and since the output voltage is fed back by the linear operation of the photocoupler, the characteristics of the photocoupler are deteriorated, especially in the space environment. There was a possibility that normal feedback could not be performed due to radiation deterioration in.

The present invention has been made in order to solve the above-mentioned problems, and provides output voltage feedback while securing insulation between the primary and secondary without using a photocoupler that may deteriorate characteristics. The purpose is to do.

[0006]

In the isolated power supply circuit according to the present invention, instead of a feedback circuit composed of a photocoupler and a shunt regulator, the output voltage is switched by a transistor and a pulse transformer, and a secondary side of the pulse transformer is provided. A rectifier circuit including a diode, a capacitor, and a resistor is provided in the.

Further, a regenerative winding and a regenerative diode are added to the pulse transformer.

[0008]

In the present invention, the transistor is switched on the secondary side in synchronism with the switching of the switching element, and the output voltage level is fed back to the primary side while achieving insulation through the pulse transformer. As a result, the control circuit performs control to stabilize the output voltage.

[0009]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, 1 to 9 are the same as the above-mentioned conventional device. 10 is a pulse transformer, 11 is a first transistor, 12 is a second transistor, 13 is a first base resistor, 14 is a second base resistor, 15 is a zener diode, 16 is a signal rectifying diode, and 17 is a signal. A smoothing capacitor, 18 is a resistor, 19 is a bias power source, 20 is a current establishing resistor, and 21 is a compensating diode.

Next, the operation will be described. 1 to 9 in FIG.
Up to this point, the operation is similar to that of the conventional circuit, and the waveforms of the respective parts on the secondary side of the power transformer 2 are shown in FIG. Between the output terminals, the primary winding of the pulse transformer 10 and the first transistor 11
Are connected in series, and the base of the first transistor 11 is connected to the output voltage side via the first base resistor 13. On the other hand, the second transistor 12 inserted between the base and the emitter of the first transistor 11 so as to have a common emitter is connected to the anode side of the free wheeling diode 6 through the second base resistor 14. It The voltage V3 on the anode side of the freewheeling diode 6 when the RTN side of the load is used as a reference has a waveform as shown in FIG. 3, so that the second transistor 12 is synchronized with ON / OFF of the switching element on the primary side. Switching is performed, and when the switch element 1 is on, it is off, and when it is off, it is on. As a result, the base signal of the first transistor is also turned on / off, so that the first transistor is also switched. The on / off timing is shown in FIG. The excitation energy of the pulse transformer 10 is absorbed by the Zener diode 15, and the pulse transformer 10 is reset while the switching is off. By this switching operation, the output voltage signal is transmitted to the secondary side of the pulse transformer 10. The transmitted signal is converted into a DC level by the signal rectifying diode 16 and the signal smoothing capacitor 17. The resistor 18 is for adjusting the frequency characteristic. Since the voltage level across the signal smoothing capacitor 17 includes the forward voltage drop of the signal rectifying diode 16, the bias power source 19 supplies the current to the RTN side of the control circuit 4 via the current establishing resistor 20 and the current via the compensating diode 21. The voltage drop in the forward direction of the signal rectifying diode 16 is canceled by flowing the current.

Although the voltage level fed back to the control circuit 4 by the above operation varies depending on the turns ratio of the pulse transformer 10, if the turns number is 1: 1, the feedback voltage matches the output voltage, and this feedback voltage causes Controls voltage stabilization.

Example 2. In the first embodiment, the excitation energy of the pulse transformer 10 is absorbed by the Zener diode 15, but as shown in FIG. 2, a winding is added to the pulse transformer 10 instead of the Zener diode 15 to regenerate the pulse transformer 10. By regenerating the excitation energy to the smoothing capacitor through the diode 22, the loss can be minimized and the same effect as that of the first embodiment can be expected.

In the above description, a transistor is used as a switching element on the secondary side, but it goes without saying that a similar circuit can be constructed by replacing it with an FET.

[0014]

As described above, according to the present invention, the switching operation is performed on the secondary side in synchronism with ON / OFF of the switching element, and the primary side is used while maintaining insulation from the secondary side by using the pulse transformer. Since the output voltage can be detected directly, there is an effect that the output voltage stabilization control can be performed accurately.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an isolated power supply circuit showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an insulated power supply circuit showing a second embodiment of the present invention.

FIG. 3 is a diagram showing waveforms of respective parts and states of switching elements and transistors according to the embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional isolated power supply circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 switching element 2 power transformer 3 drive circuit 4 control circuit 5 rectifier diode 6 freewheeling diode 7 first smoothing choke coil 8 second smoothing choke coil 9 smoothing capacitor 10 pulse transformer 11 first transistor 12 second transistor 13 second 1 base resistance 14 2nd base resistance 15 Zener diode 16 Signal rectifying diode 17 Signal smoothing capacitor 18 Resistance 19 Bias power supply 20 Current setting resistance 21 Compensation diode 22 Regeneration diode 23 Shunt regulator 24 Dividing resistor 1 25 Dividing resistor 2 26 Current limiting resistor 27 Photo coupler

Claims (1)

[Claims] 1. A switching element that switches a DC input, a power transformer that connects the switching element in series to a primary winding, and a secondary winding of the power transformer that is connected so as to conduct when the switching element is conductive. Rectifier diode, a first smoothing choke coil that enters in series with the energy transmission line from the cathode side of the rectifier diode to the load, and the other end of the secondary winding of the power transformer to which the rectifier diode is not connected. A second smoothing choke coil that enters in series with an energy transmission line that reaches the load, a freewheeling diode that releases the energy stored in the first and second smoothing choke coils when the switching element is not conducting, and a load. Is connected in parallel with the smoothing capacitor for smoothing the voltage and the switching element. In an isolated power supply circuit including a drive circuit for driving and a control circuit for supplying a drive control signal to the drive circuit, a first transistor for switching an output voltage and the first transistor are connected in series to a primary winding. Pulse transformer, a first base resistor connected from the output voltage to the base of the first transistor, and a collector / emitter of the first transistor connected in parallel to absorb the excitation energy of the pulse transformer. A zener diode, a second transistor inserted between the base and emitter of the first transistor, a second base resistor connecting the base of the second transistor and the anode of the freewheeling diode, and a pulse A signal rectifying diode connected to the secondary winding of the transformer so as to conduct when the transistor is conducting. A signal smoothing capacitor connected to the cathode side of the signal rectifying diode to peak-hold the output of the pulse transformer, a resistor connected in parallel with the signal smoothing capacitor, and a secondary winding of the pulse transformer. A compensating diode having an anode connected to the terminal not connected to the signal rectifying diode and a cathode connected to the RTN side of the control circuit, a resistor connected to the anode side of the diode, and the other end of the resistor Is connected to the bias power supply, and the voltage of the signal smoothing capacitor is fed back to the control circuit via the pulse transformer to stabilize the voltage.