Overshoot protection power supply soft start circuit and switching power supply

Abstract

The utility model discloses a power supply soft start circuit with overshoot protection and a switching power supply. The power supply soft start circuit with the overshoot protection function comprises an IC chip, a VCC input end, an HV output end, an operational amplifier, a charging circuit and a feedback circuit, the VCC input end is connected with the positive input end of the operational amplifier, the VCC input end is also connected with the charging circuit and the negative input end of the operational amplifier in sequence at the same time, and the VCC input end is also connected with the resistor R9 and a VCC pin of the IC chip in sequence at the same time; the output end of the operational amplifier is connected with the positive electrode of a diode D17, and the negative electrode of the diode D17 is connected with the FB pin of the IC chip. And the HV output end is sequentially connected with the feedback circuit and the FB pin. According to the technical scheme, soft start overshoot protection of the power supply is achieved, at the moment of electrification, the output end of the operational amplifier can output a small voltage to the FB pin, and the voltage is gradually reduced to 0V, so that the sudden change of current is small, an MOS tube with small current can be adopted, and the production cost is saved.

Description

Technical Field

[0001] The utility model relates to the technical field of switching circuits, in particular to a power supply soft start circuit with overshoot protection and a switching power supply. Background Art

[0002] In the prior art, the output duty cycle of a switching power supply is controlled according to the voltage of the FB feedback pin of its chip, and the FB voltage can automatically adjust the PWM duty cycle according to the change of the chip output voltage VCC.

[0003] Reference Figure 1 , which is the circuit diagram of the switching power supply in the prior art. Among them, when power is applied and starts up for a moment, VCC will supply power to the chip. At the same time, the voltage passes through the resistor R30, the zener diode ZD14 and the diode D17, and then a fixed voltage will be given to the FB pin. At this time, the chip outputs according to the normal PWM; when the output voltage HV starts to rise continuously until the voltage regulator U2 conducts, the fixed voltage is removed.

[0004] According to Figure 1 Substituting the data of each component shown, according to the output voltage HV of the voltage regulator U2 = (1 + (R1 + R2 + R3) / R4)*2.5 = (1 + 680*3 / 27)*2.5 = 191.38V, that is, when the HV voltage is greater than 191.38V, there will no longer be a fixed voltage supply at the FB pin, but the feedback voltage will be detected and work normally through the resistors R192, R36, and R35. The working principle of the above circuit is: first give a fixed voltage to the FB pin to start the chip, and cancel the fixed voltage before the output voltage tends to be normal, and the chip works according to the normal feedback. After rectification, the voltage, the inductor is connected in series with the D pole of the switching MOS tube. According to V = L*di / dt, when V and L are fixed, the change of di changes with dt; this leads to problems in the prior art: the time of dt is relatively long during startup, so di will also increase a lot, and the higher the withstand current of the switching MOS is required. If the withstand current of the MOS is too small, it is very easy to be broken down, but using a MOS tube with a large current will significantly increase the production cost. Summary of the Utility Model

[0005] In view of this, the utility model provides a power supply soft start circuit with overshoot protection and a switching power supply.

[0006] In the first aspect, an embodiment of the utility model provides a power supply soft start circuit with overshoot protection, including: an IC chip, a VCC input terminal, an HV output terminal, an operational amplifier, a charging circuit and a feedback circuit;

[0007] The VCC input terminal is connected to the positive input terminal of the operational amplifier. The VCC input terminal is also sequentially connected to the charging circuit and the negative input terminal of the operational amplifier, and is also sequentially connected to resistor R9 and the VCC pin of the IC chip.

[0008] The output terminal of the operational amplifier is connected to the positive electrode of diode D17, and the negative electrode of diode D17 is connected to the FB pin of the IC chip.

[0009] The HV output terminal is sequentially connected to the feedback circuit and the FB pin. As a preferred embodiment of the present invention, the VCC input terminal is connected to the charging circuit through resistor R45, and the charging circuit is also connected to the negative input terminal of the operational amplifier through resistor R37.

[0010] As a preferred embodiment of the present invention, the charging circuit includes a zener diode ZD7, a capacitor C96, a capacitor C83, and a capacitor C78 connected in parallel.

[0011] One end of the zener diode ZD7, one end of the capacitor C96, one end of the capacitor C83, and one end of the capacitor C78 are all connected between resistor R37 and resistor R45.

[0012] The other end of the zener diode ZD7, the other end of the capacitor C96, the other end of the capacitor C83, and the other end of the capacitor C78 are all grounded.

[0013] As a preferred embodiment of the present invention, the charging circuit is also sequentially connected to the positive electrode of diode D17 through resistor R37 and resistor R41.

[0014] As a preferred embodiment of the present invention, the feedback circuit includes resistors R192, R36, R35, and R34 connected in series in sequence. The HV voltage output from the HV output terminal is sequentially connected to the FB pin after passing through resistors R192, R36, R35, and R34.

[0015] As a preferred embodiment of the present invention, the feedback circuit further includes a capacitor C25 and a resistor R38.

[0016] One end of the capacitor C25 and one end of the resistor R38 are both connected to the FB pin.

[0017] The other end of the capacitor C25 and the other end of the resistor R38 are both grounded.

[0018] As a preferred embodiment of the present utility model, after the VCC input terminal is successively connected in series with resistor R42 and resistor R40, it is connected to the positive input terminal of the operational amplifier.

[0019] As a preferred embodiment of the present utility model, it further includes a filtering circuit, one end of the filtering circuit is connected to the VCC pin, and the other end of the filtering circuit is grounded.

[0020] As a preferred embodiment of the present utility model, the filtering circuit includes capacitor C22 and capacitor C24;

[0021] One end of capacitor C22 and one end of capacitor C24 are both connected to the VCC pin;

[0022] The other end of capacitor C22 and the other end of capacitor C24 are both grounded.

[0023] In a second aspect, the present utility model further provides a switching power supply, and the switching power supply includes a power soft start circuit with overshoot protection as in any embodiment of the present utility model.

[0024] The present utility model has the following beneficial effects compared with the prior art:

[0025] Through the setting of the above technical solutions in the embodiments of the present utility model, at the moment when the VCC input terminal is just powered on, due to the existence of the charging circuit, the voltage at the positive input terminal of the operational amplifier will be higher than the negative input terminal, causing the output terminal of the operational amplifier to output a voltage to the FB pin. At this time, the IC chip starts to work and outputs PWM; afterwards, as the charging of the charging circuit is completed, the voltage difference between the positive input terminal and the negative input terminal of the operational amplifier gradually decreases to 0V, and the voltage output to the FB pin also gradually decreases to 0V. At this time, the HV voltage output by the HV output terminal is output to the FB pin through the feedback circuit, enabling the IC chip to work normally. The setting of the above technical solutions can achieve soft start overshoot protection of the power supply. At the moment of power on, the output terminal of the operational amplifier can output a relatively small voltage to the FB pin and gradually decrease to 0V, resulting in a relatively small current mutation. Therefore, MOS transistors with a relatively small current can be used, thereby saving production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0027] Figure 1The circuit diagram of the power supply startup circuit in the prior art;

[0028] Figure 2 The circuit diagram of the power supply soft startup circuit with overshoot protection according to the embodiment of the present invention. Specific embodiments

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Embodiment:

[0031] In a first aspect, as Figure 2 shown, the embodiment of the present invention provides a power supply soft startup circuit with overshoot protection, including: an IC chip 10, a VCC input terminal 20, an HV output terminal 30, an operational amplifier 40, a charging circuit 50 and a feedback circuit 60;

[0032] The VCC input terminal 20 is connected to the positive input terminal of the operational amplifier 40. The VCC input terminal 20 is also sequentially connected to the charging circuit 50 and the negative input terminal of the operational amplifier 40. The VCC input terminal 20 is also sequentially connected to a resistor R9 and the VCC pin of the IC chip 10;

[0033] The output terminal of the operational amplifier 20 is connected to the positive electrode of a diode D17, and the negative electrode of the diode D17 is connected to the FB pin of the IC chip 10;

[0034] The HV output terminal 30 is sequentially connected to the feedback circuit 60 and the FB pin.

[0035] With the above technical solution, at the moment when the VCC input terminal is just powered on, due to the existence of the charging circuit, the voltage at the positive input terminal of the operational amplifier will be higher than that at the negative input terminal, causing the output terminal of the operational amplifier to output voltage to the FB pin. At this time, the IC chip starts to work and outputs PWM. After that, as the charging of the charging circuit is completed, the voltage difference between the positive input terminal and the negative input terminal of the operational amplifier gradually decreases to 0V, and the voltage output to the FB pin also gradually decreases to 0V. At this time, the HV voltage output from the HV output terminal is output to the FB pin through the feedback circuit, enabling the IC chip to work properly. The above technical solution can achieve soft start overshoot protection of the power supply. At the moment of power on, the output terminal of the operational amplifier can output a relatively small voltage to the FB pin and gradually decrease to 0V, resulting in a relatively small current mutation. Therefore, MOS transistors with a relatively small current can be used, thus saving production costs.

[0036] As a preferred embodiment of the present invention, the VCC input terminal 20 is connected to the charging circuit 50 through the resistor R45, and the charging circuit 50 is also connected to the negative input terminal of the operational amplifier 40 through the resistor R37. Among them, the charging circuit enables a certain voltage difference between the positive input terminal and the negative input terminal of the operational amplifier and gradually decreases to 0V, thereby resulting in a relatively small current mutation. Therefore, MOS transistors with a relatively small current can be used, thus saving production costs.

[0037] As a preferred embodiment of the present invention, the charging circuit includes a voltage stabilizing diode ZD7, a capacitor C96, a capacitor C83, and a capacitor C78 connected in parallel;

[0038] One end of the voltage stabilizing diode ZD7, one end of the capacitor C96, one end of the capacitor C83, and one end of the capacitor C78 are all connected between the resistor R37 and the resistor R45;

[0039] The other end of the voltage stabilizing diode ZD7, the other end of the capacitor C96, the other end of the capacitor C83, and the other end of the capacitor C78 are all grounded.

[0040] The above charging circuit can flexibly set the parameters of the capacitor so that there is a certain voltage difference between the positive input terminal and the negative input terminal of the operational amplifier.

[0041] As a preferred embodiment of the present invention, the charging circuit is also connected to the positive electrode of the diode D17 through the resistor R37 and the resistor R41 in sequence.

[0042] As a preferred embodiment of the present utility model, the feedback circuit includes a resistor R192, a resistor R36, a resistor R35, and a resistor R34 connected in series in sequence. The HV voltage output from the HV output terminal is connected to the FB pin after passing through the resistor R192, the resistor R36, the resistor R35, and the resistor R34 in sequence.

[0043] As a preferred embodiment of the present utility model, the feedback circuit further includes a capacitor C25 and a resistor R38;

[0044] One end of the capacitor C25 and one end of the resistor R38 are both connected to the FB pin;

[0045] The other end of the capacitor C25 and the other end of the resistor R38 are both grounded.

[0046] In the present utility model, the operation of the IC chip requires VCC power supply. Specifically, its PWM output and duty cycle are determined by the feedback voltage of the FB pin. Since the HV voltage output from the HV output terminal may fluctuate due to changes in the load, etc., by adopting the above technical solution, the resistor R192, the resistor R36, the resistor R35, and the resistor R34 can form a feedback upper bias resistor; the resistor R38 is a feedback lower bias resistor; the capacitor C25 is a feedback lower bias capacitor, and its main function is to adjust the operating frequency; the upper and lower bias resistors can be adjusted according to different output HV voltages.

[0047] As a preferred embodiment of the present utility model, after the VCC input terminal is connected in series with a resistor R42 and a resistor R40 in sequence, it is connected to the positive input terminal of the operational amplifier.

[0048] As a preferred embodiment of the present utility model, referring to Figure 2 , the power soft start circuit for overshoot protection further includes a filter circuit 70. One end of the filter circuit 70 is connected to the VCC pin, and the other end of the filter circuit is grounded.

[0049] As a preferred embodiment of the present utility model, the filter circuit 70 includes a capacitor C22 and a capacitor C24;

[0050] One end of the capacitor C22 and one end of the capacitor C24 are both connected to the VCC pin;

[0051] The other end of the capacitor C22 and the other end of the capacitor C24 are both grounded.

[0052] The setting of the filter circuit in the embodiment of the present utility model can filter out the ripples in the voltage entering the VCC pin.

[0053] The working principle of the power soft start circuit for overshoot protection in the embodiment of the present utility model is as follows:

[0054] Reference Figure 2 Figure 2 For the circuit shown, at the moment of power-on, the VCC power supply output from the VCC input terminal 20 will, on the one hand, be supplied to the positive input terminal of the operational amplifier 40 through resistors R42 and R40, and on the other hand, after passing through resistor R45, it will first charge capacitors C96, C83, and C78, and then be supplied to the negative input terminal of the operational amplifier 40 through resistor R37. Due to the charging delay of capacitors C96, C83, and C78 in the charging circuit, a high level is first output at the output of the operational amplifier 40, causing diode D17 to conduct, and the high level is output to the FB pin, thereby enabling the IC chip to start working normally, and the HV output terminal also outputs a voltage accordingly. As the charging of the charging circuit is gradually completed, the voltage output to the negative input terminal of the operational amplifier 40 by the charging circuit gradually increases, causing the voltage difference between the positive and negative input terminals of the operational amplifier 40 to gradually decrease to 0V, and the voltage output to the FB pin also starts to decrease and approaches 0V. At this time, the HV voltage output from the HV output terminal supplies a detection voltage to the FB pin through resistors R192, R3, R35, and R34, and the IC chip works normally.

[0055] Therefore, through the setting of the above technical solution, soft-start overshoot protection of the power supply can be achieved. At the moment of power-on, the output terminal of the operational amplifier can output a relatively small voltage to the FB pin and gradually decrease to 0V, resulting in a relatively small current mutation. Therefore, MOS transistors with a relatively small current can be used, thereby saving production costs.

[0056] Second, the present invention also provides a switching power supply, which includes a power supply soft-start circuit with overshoot protection as described in any embodiment of the present invention.

[0057] As mentioned above, the above are only the preferred embodiments of the patent of the present invention, but the protection scope of the patent of the present invention is not limited thereto. Any person skilled in the art within the scope disclosed by the patent of the present invention, according to the technical solution and the inventive concept of the patent of the present invention, makes equivalent substitutions or changes, all belong to the protection scope of the patent of the present invention.

Claims

1. A power supply soft start circuit with overshoot protection, characterized in that: include: IC chip, VCC input terminal, HV output terminal, operational amplifier, charging circuit and feedback circuit; The VCC input terminal is connected to the positive input terminal of the operational amplifier, and the VCC input terminal is also connected to the charging circuit and the negative input terminal of the operational amplifier in sequence, and the VCC input terminal is also connected to the resistor R9 and the VCC pin of the IC chip in sequence; The output end of the operational amplifier is connected to the anode of the diode D17, and the cathode of the diode D17 is connected to the FB pin of the IC chip; The HV output terminal is connected to the feedback circuit and the FB pin in sequence.

2. The power soft start circuit with overshoot protection according to claim 1, characterized in that: The VCC input terminal is connected to the charging circuit via a resistor R45, and the charging circuit is further connected to the negative input terminal of the operational amplifier via a resistor R37.

3. The power soft start circuit with overshoot protection according to claim 2, characterized in that: The charging circuit includes a voltage stabilizing diode ZD7, a capacitor C96, a capacitor C83 and a capacitor C78 connected in parallel; One end of the voltage zener diode ZD7, one end of the capacitor C96, one end of the capacitor C83 and one end of the capacitor C78 are all connected between the resistor R37 and the resistor R45; The other end of the Zener diode ZD7, the other end of the capacitor C96, the other end of the capacitor C83 and the other end of the capacitor C78 are all grounded.

4. The power soft start circuit with overshoot protection according to claim 3, characterized in that: The charging circuit is also connected to the anode of the diode D17 via the resistor R37 and the resistor R41 in sequence.

5. The power soft start circuit with overshoot protection according to claim 1, characterized in that: The feedback circuit includes a resistor R192, a resistor R36, a resistor R35 and a resistor R34 which are connected in series in sequence. The HV voltage outputted from the HV output terminal passes through the resistor R192, the resistor R36, the resistor R35 and the resistor R34 in sequence and is connected to the FB pin.

6. The power soft start circuit with overshoot protection according to claim 5, characterized in that: The feedback circuit also includes a capacitor C25 and a resistor R38; One end of the capacitor C25 and one end of the resistor R38 are both connected to the FB pin; The other end of the capacitor C25 and the other end of the resistor R38 are both grounded.

7. The power supply soft start circuit with overshoot protection according to claim 1, characterized in that: The VCC input terminal is connected to the positive input terminal of the operational amplifier after being connected in series with the resistor R42 and the resistor R40.

8. The power supply soft start circuit with overshoot protection according to claim 1, characterized in that: It also includes a filter circuit, one end of which is connected to the VCC pin, and the other end of which is grounded.

9. The power soft start circuit with overshoot protection according to claim 8, characterized in that: The filter circuit includes a capacitor C22 and a capacitor C24; One end of the capacitor C22 and one end of the capacitor C24 are both connected to the VCC pin; The other end of the capacitor C22 and the other end of the capacitor C24 are both grounded.

10. A switching power supply, characterized in that: The switching power supply comprises a power soft start circuit with overshoot protection according to any one of claims 1 to 9.

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