External synchronous input circuit of switching power supply

Abstract

The invention relates to an external synchronous input circuit of a switching power supply. The external synchronous input circuit of the switching power supply comprises a differential transformation circuit unit, a negative voltage clamping circuit unit, an emitter follower circuit unit and an oscillation signal circuit generation unit, the differential conversion circuit unit is used for converting the external synchronizing signal into a sharp pulse signal; the negative voltage clamping circuit unit is used for clamping the negative voltage part of the sharp pulse signal; the emitter follower circuit unit is used for isolating external disturbance and amplifying the driving capability of the spike pulse signal; and the oscillation signal circuit generation unit is used for controlling the UCX843 control chip to generate an oscillation signal. When the external synchronous input end of the switching power supply is grounded, an external interference signal on the power ground can be isolated by the triode of the emitter follower, and meanwhile, by adopting the external synchronous input circuit of the switching power supply, the driving capability of the external synchronous signal can be improved, the external synchronous frequency range can be increased, and the adaptability of the circuit can be enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of switching power supplies, and in particular to an external synchronous input circuit of a switching power supply. Background Art

[0002] When multiple independently oscillating switching power supply modules are connected in parallel, the output voltage ripple will cause differential frequency interference between the power supplies. In order to eliminate differential frequency interference, the oscillation frequency between the power supplies must be synchronized. Some power supply control chips themselves have external synchronization pins (such as pin 3 of UCX525). The power supply controlled by such chips can be directly designed with the external synchronization function through the external synchronization pin of the control chip. Some power supply control chips themselves do not have external synchronization pins (such as UCX843). The power supply controlled by such chips needs to use an external circuit to realize the external synchronization function.

[0003] The recommended external synchronization circuit of the existing UCX843 control chip is mainly realized by the RC differential circuit composed of Csyn and R2 and the oscillation circuit of the control chip itself. Although the circuit has a simple structure, it has several shortcomings: first, the anti-interference ability is not strong. If the external synchronization end (SYNC pin) of the power module is connected to the external ground, the interference signal on the ground line may enter the control chip through the Csyn capacitor, affecting the normal operation of the control chip and thus affecting the normal operation of the power module; second, the driving ability of the external synchronization signal is high, the external synchronization frequency range is small, and the adaptability is poor. Third, when the external synchronization end is grounded, it will affect the switching frequency of the power module. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, an object of the present invention is to provide an external synchronous input circuit for a switching power supply.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A switching power supply external synchronous input circuit comprises: a differential conversion circuit unit, a negative voltage clamping circuit unit, an emitter follower circuit unit and an oscillation signal circuit generating unit.

[0007] The differential conversion circuit unit is used to convert the external synchronization signal into a sharp pulse signal.

[0008] The negative voltage clamping circuit unit is used to clamp the negative voltage part of the sharp pulse signal.

[0009] The emitter follower circuit unit is used to isolate external step interference and amplify the driving capability of the peak pulse signal.

[0010] The oscillation signal circuit generating unit is used to control the UCX843 control chip to generate an oscillation signal.

[0011] Preferably according to the present invention, the differential transformation circuit unit includes a capacitor C1, a resistor R1 and a resistor R2; the first end of the capacitor C1 is connected to the external synchronization signal, the second end is connected to the first end of the resistor R1, the second end of the resistor R1 is connected to the first end of the resistor R2, and the second end of the resistor R2 is grounded.

[0012] Preferably according to the present invention, the external synchronization signal adopts TTL level, and the external synchronization signal obtains a sharp pulse signal with the same frequency as the external synchronization signal through the differential transformation circuit unit, and the amplitude of the sharp pulse signal is adjusted by the resistance values ​​of the resistor R1 and the resistor R2.

[0013] Preferably according to the present invention, the negative voltage clamping circuit unit includes a diode V1; the anode of the diode V1 is grounded, and the cathode is connected to the first end of the resistor R1 and the resistor R2; the diode V1 is used to control the negative voltage part of the sharp pulse signal below 0.6V.

[0014] Preferably according to the present invention, the emitter follower circuit unit comprises a transistor V2, the base of the transistor V2 is connected to the cathode of the diode V1, and the collector is connected to the reference voltage terminal of the UCX843 control chip.

[0015] Preferably according to the present invention, the oscillation signal generating unit includes a resistor R3, a capacitor C2 and a resistor R4; the first end of the resistor R3 is connected to the reference voltage end of the UCX843 control chip, and the second end is connected to the first end of the capacitor C2, the second end of the capacitor C2 is connected to the first end of the resistor R4, and the second end of the resistor R4 is grounded; the first end of the resistor R3 is also connected to the collector of the transistor V2; the emitter of the transistor V2 is respectively connected to the second end of the capacitor C2 and the first end of the resistor R4.

[0016] Preferably according to the present invention, the oscillation pin of the UCX843 control chip is connected to the second end of the resistor R3 and the first end of the capacitor C2 respectively.

[0017] Preferably according to the present invention, the transistor V2 is an NPN transistor.

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] By adopting the switching power supply external synchronous input circuit of the present invention, when the external synchronous input terminal of the switching power supply is grounded, the external interference signal on the power ground will be isolated by the transistor of the emitter follower. At the same time, by adopting the switching power supply external synchronous input circuit of the present invention, the driving capability of the external synchronous signal can be increased, the external synchronous frequency range can be increased, and the adaptability of the circuit can be enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The invention discloses a circuit diagram of an external synchronous input circuit of a switching power supply. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings:

[0022] like Figure 1 A switching power supply external synchronous input circuit is shown, and the switching power supply external synchronous input circuit includes: a differential conversion circuit unit, a negative voltage clamping circuit unit, an emitter follower circuit unit and an oscillation signal circuit generating unit.

[0023] The switching power supply external synchronous input circuit of the present invention is designed and implemented for the UCX843 control chip. Figure 1 As shown, the functions of each port of the UCX843 control chip are as follows:

[0024] (1) VREF is a reference voltage input port used to provide a stable reference voltage for an analog-to-digital converter (ADC) or some comparators.

[0025] (2) VFB is the feedback voltage port, which is used to monitor the output voltage and adjust it.

[0026] (3) RT / CT is a resistor / capacitor terminal used to set the frequency of a timer or oscillator.

[0027] (4) VCC is the power supply voltage port, which provides the positive voltage required for the IC to work.

[0028] (5) CS is the chip select signal, which is used to select a specific IC.

[0029] (6) COMP is the comparator output or compensation port.

[0030] (7) OUTPUT is the output port.

[0031] (8) GND is the ground port.

[0032] The differential conversion circuit unit is used to convert the external synchronization signal into a sharp pulse signal. The differential conversion circuit unit includes a capacitor C1, a resistor R1 and a resistor R2; the first end of the capacitor C1 is connected to the external synchronization signal, the second end is connected to the first end of the resistor R1, the second end of the resistor R1 is connected to the first end of the resistor R2, and the second end of the resistor R2 is grounded. The external synchronization signal adopts a TTL level, and the external synchronization signal obtains a sharp pulse signal with the same frequency as the external synchronization signal through the differential conversion circuit unit, and the amplitude of the sharp pulse signal is adjusted by the resistance values ​​of the resistor R1 and the resistor R2. The function of this circuit is to convert the external TTL level signal into a sharp pulse signal with adjustable amplitude so as to be superimposed with the oscillation signal of UCX843, so that the original frequency of the UCX843 control chip is consistent with the frequency of the external signal.

[0033] The negative voltage clamping circuit unit is used to clamp the negative voltage part of the sharp pulse signal. The negative voltage clamping circuit unit includes a diode V1; the anode of the diode V1 is grounded, and the cathode is connected to the first end of the resistor R1 and the resistor R2; the diode V1 is used to control the negative voltage part of the sharp pulse signal to be below 0.6V to avoid the negative voltage when it is superimposed with the oscillation signal of UCX843.

[0034] The emitter follower circuit unit is used to isolate external interference and amplify the driving capability of the peak pulse signal. The emitter follower circuit unit includes a transistor V2, the base of which is connected to the cathode of the diode V1, and the collector is connected to the reference voltage terminal of the UCX843 control chip.

[0035] The oscillation signal circuit generating unit is used to control the UCX843 control chip to generate an oscillation signal. The oscillation signal generating unit includes a resistor R3, a capacitor C2 and a resistor R4; the first end of the resistor R3 is connected to the reference voltage end of the UCX843 control chip, the second end is connected to the first end of the capacitor C2, the second end of the capacitor C2 is connected to the first end of the resistor R4, and the second end of the resistor R4 is grounded; the first end of the resistor R3 is also connected to the collector of the transistor V2; the emitter of the transistor V2 is respectively connected to the second end of the capacitor C2 and the first end of the resistor R4. The oscillation pin of the UCX843 control chip is respectively connected to the second end of the resistor R3 and the first end of the capacitor C2. The transistor V2 is an NPN transistor.

[0036] By adopting the switching power supply external synchronous input circuit of the present invention, when the external synchronous input terminal of the switching power supply is grounded, the external interference signal on the power ground will be isolated by the transistor of the emitter follower. At the same time, by adopting the switching power supply external synchronous input circuit of the present invention, the driving capability of the external synchronous signal can be increased, the external synchronous frequency range can be increased, and the adaptability of the circuit can be enhanced.

[0037] The above-described embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the scope of protection determined by the claims of the present invention.

Claims

1. A switching power supply external synchronous input circuit, characterized in that: The external synchronous input circuit of the switching power supply comprises: a differential conversion circuit unit, a negative voltage clamping circuit unit, an emitter follower circuit unit and an oscillation signal circuit generating unit; The differential conversion circuit unit is used to convert the external synchronization signal into a sharp pulse signal; The negative voltage clamping circuit unit is used to clamp the negative voltage part of the sharp pulse signal; The emitter follower circuit unit is used to isolate external interference and amplify the driving capability of the peak pulse signal; The oscillation signal circuit generating unit is used to control the UCX843 control chip to generate an oscillation signal.

2. The switching power supply external synchronous input circuit according to claim 1, characterized in that: The differential conversion circuit unit includes a capacitor C1, a resistor R1 and a resistor R2; The first end of the capacitor C1 is connected to the external synchronization signal, the second end is connected to the first end of the resistor R1, the second end of the resistor R1 is connected to the first end of the resistor R2, and the second end of the resistor R2 is grounded.

3. The switching power supply external synchronous input circuit according to claim 2, characterized in that: The external synchronization signal adopts TTL level, and the external synchronization signal obtains a sharp pulse signal with the same frequency as the external synchronization signal through the differential conversion circuit unit, and the amplitude of the sharp pulse signal is adjusted by the resistance values ​​of the resistor R1 and the resistor R2.

4. The switching power supply external synchronous input circuit according to claim 3, characterized in that: The negative voltage clamping circuit unit includes a diode V1; the anode of the diode V1 is grounded, and the cathode is connected to the first end of the resistor R1 and the resistor R2; The diode V1 is used to control the negative voltage portion of the spike pulse signal to be below 0.6V.

5. The switching power supply external synchronous input circuit according to claim 1, characterized in that: The emitter follower circuit unit comprises a transistor V2, the base of the transistor V2 is connected to the cathode of the diode V1, and the collector is connected to the reference voltage terminal of the UCX843 control chip.

6. The switching power supply external synchronous input circuit according to claim 5, characterized in that: The oscillation signal generating unit includes a resistor R3, a capacitor C2 and a resistor R4; The first end of the resistor R3 is connected to the reference voltage end of the UCX843 control chip, and the second end is connected to the first end of the capacitor C2. The second end of the capacitor C2 is connected to the first end of the resistor R4, and the second end of the resistor R4 is grounded; the first end of the resistor R3 is also connected to the collector of the transistor V2; the emitter of the transistor V2 is respectively connected to the second end of the capacitor C2 and the first end of the resistor R4.

7. The switching power supply external synchronous input circuit according to claim 6, characterized in that: The oscillation pin of the UCX843 control chip is connected to the second end of the resistor R3 and the first end of the capacitor C2 respectively.

8. The switching power supply external synchronous input circuit according to claim 5, characterized in that: The transistor V2 is an NPN transistor.

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