TW201419723A - Switching power converting circuit capable of outputting a preset current, method therefore and manufacturing method of IC with the same circuit - Google Patents

Abstract

A switching power converting circuit capable of outputting a preset current, method therefore and manufacturing method of IC with the same circuit. A sample/hold circuit samples a current sense signal corresponding to a current flowing through a high-side transistor switch in current-outputting path at a timing substantially concurrently with the conducting of the high-side transistor switch, and holds the sampled signal at a high level at the remaining timing. A current error amplifier outputs a current error signal according to the output of the sample/hold circuit and a preset current reference signal. When the preset current is output, a comparator outputs a PWM signal to control the ON/OFF duty cycle of the high-side transistor switch and the low-side transistor switch, so as to regulate the output current to a preset level.

Description

Switching power conversion circuit capable of constant current output, power conversion method thereof and Manufacturing method of integrated circuit having the circuit

The present invention relates to a switching power converter, and more particularly to a pulse width modulation method, having an output current monitoring circuit capable of adjusting an output pulse width according to a monitored output current amount to achieve a stable output of a preset current amount. A switching power conversion circuit capable of constant current output, a power conversion method thereof, and a manufacturing method of an integrated circuit having the same.

Figure 1 is a circuit diagram of a buck-type constant current output switching power converter.

Referring to FIG. 1 , the switching power converter 10 includes a high-level transistor switch M _H , a low-level transistor switch M _L , a controller 12 , an inductor 14 , a capacitor 16 , and a current sensing resistor 18 .

The controller 903 connects the gate of the upper transistor switch M _H with the gate of the lower transistor switch M _L and controls the switching timing of the upper transistor switch M _H and the lower transistor switch M _L . The anode of the high-position transistor switch M _H is connected to the power input PIN, and the cathode of the high-position transistor switch M _H is connected to the anode of the low-position transistor switch M _L . The negative terminal connected to the lower transistor switch M _L is connected to the negative power supply PGND. The first end of the inductor 14 is connected to the cathode of the high-position transistor switch M _{H and} the cathode of the low-level transistor switch M _L , and the second end of the inductor 14 is connected to the first end of the current sensing resistor 18 . The second end of current sense resistor 18 is coupled to the positive terminal of capacitor 16 and the positive terminal of load 20. The negative pole of the capacitor 16 and the negative pole of the load 20 are connected to the negative pole PGND of the power source.

Wherein, when the transistor switch (ie, the high-position transistor switch M _H or the low-position transistor switch M _L ) uses a PMOS, the positive electrode is the source and the negative electrode is the drain. When the transistor switch uses an NMOS, the positive electrode is a drain and the negative electrode is a source.

In current monitoring, the output current amount signal is derived from the potential difference V _R across the measured current sense resistor 18 and the resistance value of the known current sense resistor 18 based on the equation that the current is equal to the voltage divided by the resistance. Then, the output current amount signal is fed back to the pulse width modulation circuit to adjust the output pulse width, thereby adjusting the amount of the output current I _L .

However, on the switched power converter 10, since all of the output current I _L flows through the current sense resistor 18, the energy consumed is very large. Moreover, in order to minimize the energy consumption of the current sensing resistor 18, the current sensing resistor 18 must use a low resistance resistor element as much as possible. However, the lower the resistance, the more difficult it is to make the manufacturing error accuracy, so the cost of the resistor element that is acceptable for the error value is relatively high.

Figure 2 is a circuit diagram of another buck-type constant current output switching power converter.

Referring to Fig. 2, the switching power converter 10' differs from the above-described switching power converter 10 in that the switching power converter 10' omits the current sensing resistor 18. Here, in the current monitoring, the inductor 14 itself has the property of having an equivalent DC resistance.

In the switched power converter 10', a filter line 19 connected in series by a filter resistor Rf and a filter capacitor Cf is connected across the inductor 14, whereby the filter line 19 monitors the potential difference V _L across the inductor 14. The output current amount signal is derived from the measured potential difference V _L across the inductor 14 and the known DC resistance value of the inductor 14 based on a formula in which the current is equal to the voltage divided by the resistance. Then, the output current amount signal is fed back to the pulse width modulation circuit to adjust the output pulse width, thereby adjusting the amount of the output current I _L .

However, on the switched-mode power converter 10', the practical inductor 14 has a relatively low DC resistance value, and the difference in DC resistance between the inductors of the same specification is often higher than 20%, resulting in the same actual installation. In the finished product of the switched-type power converter of the specification inductor, the sensed theoretical output current amount and the actual output current amount respectively are excessively large.

In one embodiment, a switchable power conversion circuit capable of constant current output includes: a power input contact, a power output contact, a power conversion circuit, a current sensing circuit, a sample/hold circuit, and a signal A generating circuit, a current error amplifier, and a comparator are provided.

The power conversion circuit is electrically connected between the power input contact and the power output contact, and the power conversion circuit includes a first high level transistor switch and a low level transistor switch. The first high-level transistor switch and the low-level transistor switch are alternately turned on according to a pulse width modulation signal. The current sensing circuit is configured to generate a current sense voltage signal corresponding to one of the currents passing through the first high level transistor switch.

Here, the sampling period of the sample/hold circuit is substantially synchronized with the on period of the first high level transistor switch. During sampling, the sample/hold circuit outputs a current monitoring signal based on the current sense voltage signal. During hold, the sample/hold circuit outputs a current monitoring signal that remains at a high level.

The current error amplifier outputs a current error signal according to the current monitoring signal and the current reference voltage signal generated by the signal generating circuit. Output one at the power output contact When the current is constant, the comparator outputs a pulse width modulation signal according to a sawtooth signal and a current error signal.

In some embodiments, the switchable power conversion circuit of the current output can be packaged as an integrated circuit.

In another embodiment, a method for manufacturing an integrated circuit includes: providing a power input terminal and a power output terminal on an integrated circuit; and electrically connecting the power input terminal and the power output in the integrated circuit; a power conversion circuit between the terminals, wherein the power conversion circuit includes a high-level transistor switch and a low-level transistor switch alternately turned on according to a pulse width modulation signal; a current sensing circuit is disposed in the integrated circuit, The current flowing through the high-level transistor switch is sensed when the high-position transistor switch is turned on, and a current-sensing voltage signal is output; a sample/hold circuit is disposed in the integrated circuit to output a current-sensing voltage signal and output a a current monitoring signal and maintaining a current sensing voltage signal when the high-level transistor switch is not conducting; a signal generating circuit is disposed in the integrated circuit to generate a current reference voltage signal; and a current error amplifier is disposed in the integrated circuit And outputting a current error signal according to the current monitoring signal and the current reference voltage signal; and the integrated circuit therein A comparator is arranged to output a pulse width modulation signal according to a sawtooth signal and a current error signal when the power output contact outputs a certain current.

In still another embodiment, a switchable power conversion method for a constant current output includes: alternately turning on a first high level transistor switch and a low level transistor switch according to a pulse width modulation signal; sensing through the first high level a current of the transistor switch to generate a current sense voltage signal corresponding to one of the currents through the first high level transistor switch; sampling with a sample/hold switch during the turn-on of the first high level transistor switch The current senses the voltage signal to output a current monitoring signal according to the current sensing voltage signal; and the current sensing voltage signal is held by the sample/hold switch during the non-conduction of the first high-level transistor switch to output the current monitoring at a high level a signal; outputting a current error signal according to the current monitoring signal and a current reference voltage signal; and outputting a pulse width modulation signal according to a sawtooth signal and a current error signal when the power output contact outputs a certain current.

Wherein, the first high-level transistor switch is disposed on a first current path between a power input contact and a power output contact, and the low-level transistor switch is disposed at the power input contact and a negative contact of the power supply. A second current path between the power supply output contact and the power supply negative contact.

In summary, in the switching power conversion circuit of the constant current output according to the present invention, the power conversion method thereof, and the manufacturing method of the integrated circuit having the circuit, in addition to the current output path (ie, the power conversion circuit), A current shunt path parallel to the current output path (especially an active shunt circuit parallel to the high-level transistor switch or the high-position transistor switch) is provided. The current flowing through the current shunt path is relatively small compared to the current flowing through the high-level transistor switch in the current output path and is proportional to both. In some embodiments, the second input of the current error amplifier is coupled to a voltage source (ie, a signal generating circuit) that can be set by the user.

In operation, the current forced through the active shunt circuit is a fixed fraction of the current flowing through the high-level transistor switch in the current output path (ie, one-nth), so that the active shunt can be monitored through the flow. The amount of current in the circuit is used to calculate the amount of output current flowing through the high-level transistor switch. Moreover, in the same pulse period, the average value of the current flowing through the high-level transistor switch in the upper half cycle is lower than that in the second half cycle. The average of the currents of the bit transistor switches are approximately equal. Therefore, the average output current amount of the entire circuit (or integrated circuit) can be obtained by monitoring the average value of the current flowing through the active shunt line when the high-position transistor switch is turned on. Furthermore, after the current sensing voltage signal is filtered by the sample/hold circuit, the amplitude of the output current monitoring signal is reduced and approaches the average of the original potential difference. Because the voltage rise and fall rate of the signal output by the current error amplifier is lower than the voltage rise and fall rate of the input signal (ie, the bandwidth of the amplifier is lower than the input signal frequency), and is higher than the received frequency of the first input terminal. The frequency signal (current monitoring signal) is equivalent to a low-pass filter, so that the input current monitoring signal not only reduces the amplitude of the chopping but also effectively avoids the subharmonic oscillation.

The switching power conversion circuit capable of constant current output according to the present invention, the power conversion method thereof, and the manufacturing method of the integrated circuit having the same can be applied to, for example, a charger of a battery or a driver of a light emitting diode, etc., which are required to be externally loaded When a fixed current is output.

In the following terms, "first" and "second" are used to distinguish the elements referred to, and unless otherwise stated, such terms are not used to rank or limit the differences of the elements referred to, and It is intended to limit the scope of the invention.

Fig. 3 is a view showing a switching power supply switching circuit of a constant current output according to the first embodiment of the present invention.

Referring to FIG. 3, the switching power conversion circuit capable of constant current output includes a power input contact 111, a power output contact 112, a power negative contact 113, a current setting contact 114, and a voltage feedback contact. 115, a power conversion circuit 120, A current sensing circuit 130, a sample/hold circuit 140, a current error amplifier 150, an error signal selector 152, a voltage error amplifier 154, a signal generating circuit 160, a comparator 170, and a controller 180.

The power conversion circuit 120 includes a plurality of transistor switches, and the transistor switches are turned on in response to the high level signal and the low level signal, respectively. For clarity, the following are referred to as high-level transistor switches and low-level transistor switches, respectively.

It should be understood that the transistor switch (such as a high-level transistor switch or a low-level transistor switch) in the figure is exemplified by a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET). However, this is not a limitation of the present invention, and other similar components may be used, such as an insulated gate bipolar transistor (IGBT).

Among them, when the transistor switch uses a PMOS (p-channel MOSFET), the positive electrode is the source, the negative electrode is the drain, and the gate is controlled extremely. When the transistor switch uses an NMOS (n-channel MOSFET), the positive electrode is a drain, the negative electrode is a source, and the gate is controlled extremely.

In this embodiment, the power conversion circuit 120 is a switching step-down power conversion circuit. In other words, the switching power conversion circuit capable of setting the current output is a step-down switching power converter circuit. Here, the power conversion circuit 120 includes a high level transistor switch 122 and a low level transistor switch 124.

The anode of the high level transistor switch 122 is connected to the power source input contact 111, and the cathode of the high level transistor switch 122 and the anode of the low level transistor switch 124 are commonly connected to the power source output contact 112. The cathode of the lower transistor switch 124 is connected to the power source negative contact 113. The control electrode of the high level transistor switch 122 is connected to the high level of the controller 180 The signal output terminal and the control electrode of the low-level transistor switch 124 are connected to the low-level signal quasi-output terminal of the controller 180. The input of controller 180 is coupled to the output of comparator 170.

The first end of the external external inductor 22 is connected to the power supply output contact 112, and the second end of the external inductor 22 is connected to the first end of the external load 20 and the positive terminal of the external output capacitor 24. The second end of the load 20 and the negative terminal of the output capacitor 24 are connected to the negative supply contact 113 of the power supply.

The controller 180 receives the pulse width modulation signal outputted by the comparator 170, and outputs a signal according to the pulse width modulation signal to control the high level transistor switch 122 and the low level transistor switch 124 to be alternately turned on and off.

When the high level transistor switch 122 is turned on (turned on), the low level transistor switch 124 is not turned on (turned off). At this time, the output current I _L sequentially flows through the power input contact 111, the high transistor switch 122, the power output contact 112, the external inductor 22, the output capacitor 24 (to be filtered by the output capacitor 24), and the load. 20, finally return to the negative pole contact 113 of the power supply.

When the high level transistor switch 122 is not turned "on" (off), the low level transistor switch 124 is turned "on". At this time, the magnetic energy stored in the external inductor 22 is converted into the output current I _L , and the converted output current I _L sequentially flows through the output capacitor 24 (to be filtered by the output capacitor 24), the load 20, and the negative pole of the power supply. The contact 113, the low transistor switch 124, and the power output contact 112 are finally returned to the external inductor 22.

In some embodiments, power conversion circuit 120, current sensing circuit 130, sample/hold circuit 140, current error amplifier 150, error signal selector 152, voltage error amplifier 154, signal generation circuit 160, comparator 170, and controller 180 can be packaged into an integrated circuit 100. In other words, the power conversion circuit 120, the current sensing circuit 130, the sample/hold circuit 140, the current error amplifier 150, the error signal selector 152, the voltage error amplifier 154, the signal generating circuit 160, the comparator 170, and the controller 180 are disposed at The inside of an integrated circuit. At this time, the power input contact 111, the power output contact 112, the power negative contact 113, the current setting contact 114, and the voltage feedback contact 115 are external terminals of the integrated circuit 100. That is, the power input contact 111 is a power input positive terminal to which the integrated circuit 100 is coupled to the external line, and is used to receive the power input V _IN from the external line. The power output contact 112 is a power input positive terminal for the integrated circuit 100 to be coupled to the external line, and is used to provide a power output V _OUT to the external line. The power source negative contact 113 is a power source negative terminal for the integrated circuit 100 to be coupled to the external line, and is coupled to a reference level of the external line (eg, ground). The current setting contact 114 is a current setting terminal for the integrated circuit 100 to be coupled to the external line, and is configured to receive the set current Iset from the external line. The voltage feedback contact 115 is a voltage feedback terminal for the integrated circuit 100 to be coupled to the external line, and is configured to receive the feedback signal V _FB from the external line.

The external components (for example, the load 20, the external inductor 22, the output capacitor 24, the setting resistor 26, and the like) are disposed outside the integrated circuit 100, and are electrically connected to the external terminals of the integrated circuit 100. The internal circuitry of circuit 100.

The current sensing circuit 130 includes an active shunt circuit 131 and a current sensing resistor 135. The active shunt circuit 131 includes a high level transistor switch 132 and a potential balancing circuit 134 formed by the operational amplifier OP1 and the transistor M1. For convenience of explanation, in the following, the high-position transistor switch 122 is referred to as a first high-level electric crystal. The body switch 122, the high level transistor switch 132 is referred to as a second high level transistor switch 132, and the potential balance circuit 134 is referred to as a first potential balance circuit 134.

The anode of the second high level transistor switch 132 and the anode of the first high level transistor switch 122 are commonly connected to the power input contact 111. The gate of the second high level transistor switch 132 and the gate of the first high level transistor switch 122 are commonly coupled to the high level signal output of the controller 180. The negative terminal of the first high-order transistor switch 122 and the negative terminal of the second high-position transistor switch 132 are respectively connected to the two input terminals of the operational amplifier OP1, and the output terminal of the operational amplifier OP1 is connected to the gate electrode of the transistor M1. The negative electrode of the second high level transistor switch 132 is further connected to the positive electrode of the transistor M1.

Since the potentials of the two input terminals of the operational amplifier OP1 are forced to be the same, the potential of the negative electrode of the first high-order transistor switch 122 and the potential of the negative electrode of the second high-position transistor switch 132 are also forced to be the same. Further, since the anode of the first high-position transistor switch 122 and the anode of the second high-position transistor switch 132 are connected, the potential of the anode of the first high-position transistor switch 122 and the potential of the anode of the second high-position transistor switch 132 are also the same. .

Here, the material and manufacturing process of the second high level transistor switch 132 are the same as the first high level transistor switch 122, but the scale of the second high level transistor switch 132 is a fixed fraction of the first high level transistor switch 122, ie, n. One step, so the on-resistance between the positive and negative electrodes of the second high-position transistor switch 132 is n times the on-resistance between the positive and negative electrodes of the first high-position transistor switch 122. Since the voltage drop between the positive pole and the negative pole of the first high level transistor switch 122 and the second high level transistor switch 132 is the same, the on resistance of the second high level transistor switch 132 is the conduction of the first high level transistor switch 122. The resistance is n times, so the current I _S flowing through the second high-position transistor switch 132 is one-nth of the current I _M flowing through the first high-position transistor switch 122.

For example, assume that the rated operating current of the first high level transistor switch 122 is 2 amps. With the current semiconductor manufacturing technology, a second high-order transistor switch 132 with a rated operating current of 2 amps can be easily fabricated, so that the energy lost due to the demand for monitoring current becomes negligible.

It should be understood that the first potential balancing circuit 134 has many different designs and is not limited to the design disclosed in the embodiment shown in FIG. In other embodiments of the invention, the first potential balancing circuit 134 can employ other suitable designs.

The end series current sensing resistor 135 of the active shunt circuit 131 is grounded. In other words, the first end of the current sense resistor 135 is connected to the negative terminal of the transistor Ms, and the second end of the current sense resistor 135 is connected to the signal ground.

The current I _S flowing through the second upper transistor switch 132 also flows through the current sense resistor 135, and a potential difference (V _SENSE ) is formed across the current sense resistor 135. The value of this potential difference (V _SENSE ) is equal to one-nth of the current I _M flowing through the first high-position transistor switch 122 multiplied by the resistance value (R _SENSE ) of the current-sensing resistor 135, as shown in the following Equation 1.

Therefore, this potential difference (V _SENSE ) can be used to proportionally represent the value of the current I _M flowing through the first high-position transistor switch 122.

In other words, the amount of current flowing through the current sensing resistor 135 is also one-nth of the current I _M flowing through the first high-position transistor switch 122, and the average value thereof is approximately equal to the entire circuit (or the integrated circuit 100 having the circuit) One of n of the average value of the output current I _L . Therefore, the average value of the potential difference across the current sense resistor 135 is substantially equal to the resistance value of the current sense resistor 135 multiplied by one-nth of the average value of the output current I _L of the entire circuit (or the entire integrated circuit 100).

The current sense voltage signal of the above potential difference (V _SENSE ) is input to a sample/hold circuit 140.

The sample/hold circuit 140 includes a sample/hold switch 142 and a low pass filter 144. The low pass filter 144 is a resistor-capacitor low pass filter formed by the resistor 145 and the holding capacitor 146.

The first end of the sample/hold switch 142 is coupled to the end of the active shunt circuit 131 and the first end of the current sense resistor 135 and receives a current sense voltage signal having the above potential difference (V _SENSE ). The second end of the sample/hold switch 142 is coupled to the first end of the resistor 145. A second end of the resistor 145 is coupled to the first terminal of the holding capacitor 146 and the first input of the current error amplifier 170. The second end of the holding capacitor 146 is grounded.

The control terminal of the sample/hold switch 142 is connected to the controller 180, and a signal is output from the controller 180 to control the operation of the sample/hold switch 142 (on or off). Here, the on period (ie, the sampling period) of the sample/hold switch 142 is substantially synchronized with the on period of the high level transistor switches 122, 132.

During sampling, the sample/hold switch 142 outputs a current monitoring signal based on the current sense voltage signal. During hold, the sample/hold switch 142 maintains the current sense voltage signal at a high level and outputs a current monitor signal that remains at a high level. The current monitoring signal is filtered via low pass filter 144 and input to a first input of current error amplifier 170.

In other words, during the conduction of the first high-position transistor switch 122, the external inductor 22 is charged by the current I _M of the first high-position transistor switch 122, and the output of the external inductor 22 is reflected at both ends of the current-sensing resistor 135. The rising period of the current I _L (ie, the charging current of the external inductor 22) generates a current sensing voltage signal (potential difference V _SENSE ). After the current sense voltage signal passes through the sample/hold circuit 140 having the low pass filtering function, its signal chopping amplitude is reduced and approaches the average value of the rising portion (original potential difference V _SENSE ) of the output current I _L of the original external inductor 22 . The filtered current sense voltage signal (ie, current monitor signal) is again input to the first input of current error amplifier 150.

Since the current error amplifier 150 has a voltage rise and fall rate of the output signal that is lower than the voltage rise and fall rate of the input signal (ie, the bandwidth of the current error amplifier 150 is lower than the frequency of the input signal), and the current error amplifier 150 is relative to The high frequency signal received by the first input is in turn equivalent to a low pass filter, so that the input signal (ie, the current monitoring signal) not only further reduces the amplitude of the chopping but also effectively avoids subharmonic oscillation.

A second input of current error amplifier 150 is coupled to signal generation circuit 160 and receives a set current reference voltage signal generated by signal generation circuit 160. The current error amplifier 150 amplifies the current reference voltage signal and the current monitoring signal to output a current error signal to the first input of the error signal selector 152.

In some embodiments, signal generation circuit 160 includes a current to voltage converter 162 and a potential balancing circuit 164. For clarity of explanation, in the following, the potential balancing circuit 164 is referred to as a second potential balancing circuit 164.

The second potential balancing circuit 164 includes an operational amplifier OP2 and a transistor M2. The first input terminal of the operational amplifier OP2 is connected to a reference set potential Vset generated inside the integrated circuit 100, and the second input terminal of the operational amplifier OP2 and the negative electrode of the transistor M2 are commonly connected to the current setting contact 114. The output of operational amplifier OP2 is coupled to the gate of transistor M2, and current to voltage converter 162 is coupled between the positive terminal of transistor M2 and the second input of current error amplifier 150.

The second potential balance circuit 164 forcibly sets the potential of the current setting contact 114 to be the same as the reference set potential Vset generated inside the integrated circuit 100. Moreover, the user connects a set resistor 26 between the current setting contact 114 and the signal ground. The resistance value of this set resistor 26 is represented by Rset. As a result, the value of the current Iset flowing through the current setting contact 114 is fixed to Vset/Rset. The current Iset is converted into a voltage signal by the current-to-voltage converter 162, and the voltage signal is input to the second input terminal of the current error amplifier 150 as a current reference signal.

The current-to-voltage converter 162 includes a current-to-voltage conversion resistor 163. Here, the current-voltage conversion resistor 163 and the current-sensing resistor 136 are fabricated on the same integrated circuit 100 in the same batch of materials at the same time and at the same time, so the manufacturing error direction (positive or negative) and degree of the two are substantially the same. For example, on a certain product, the actual resistance values of the current-voltage conversion resistor 163 and the current-sensing resistor 136 are both 10% higher than the design value, and the current reference signal and current monitoring respectively generated by the two resistors are respectively monitored. The signals are also 10% higher than the theoretical value. Therefore, when the current reference signal and the current monitoring signal are amplified by error, the manufacturing errors of the two cancel each other out.

A second input of error signal selector 152 is coupled to the output of voltage error amplifier 154. The first input of the voltage error amplifier 154 is electrically connected to the voltage The feedback point 115 is returned.

A voltage detecting point 21 may be disposed near the positive pole of the load 20, and the voltage detecting point 21 is electrically connected to the voltage feedback contact 115.

In some embodiments, a feedback circuit 190 can be provided on the feedback path between the voltage detection point 21 and the first input of the voltage error amplifier 154. The feedback circuit 190 is configured to proportionally adjust the feedback voltage from the voltage detection point 21 and output a voltage monitoring signal to the voltage error amplifier 154.

In some embodiments, the feedback circuit 190 can be disposed external to the integrated circuit 100, that is, between the voltage detection point 21 and the voltage feedback contact 115.

In some embodiments, the feedback circuit 190 can also be disposed internal to the integrated circuit 100, that is, between the voltage feedback contact 115 and the first input of the voltage error amplifier 154.

In some embodiments, the feedback circuit 190 can be a voltage dividing resistor circuit, and the voltage dividing resistor of the voltage dividing resistor circuit is electrically connected to the first input terminal of the voltage error amplifier 154.

At this time, the feedback circuit 190 proportionally reduces the external voltage feedback signal input from the voltage feedback contact 115 and outputs a voltage monitoring signal to the first input terminal of the voltage error amplifier 154. The second input of the voltage error amplifier 154 receives the voltage reference signal Vref generated inside the integrated circuit 100. The voltage error amplifier 154 amplifies the voltage reference signal Vref and the voltage monitoring signal to output a voltage error signal to the second input of the error signal selector 152.

According to different circuit designs, the error signal selector 152 determines whether the voltage of the external load 20 is higher than a predetermined voltage threshold based on the level of the voltage monitoring signal. When negative The error signal selector 152 outputs a current error signal to the first input of the comparator 170 when the voltage of the load 20 is below a predetermined voltage threshold. When the voltage of the load 20 is above a predetermined voltage threshold, the error signal selector 152 outputs a voltage error signal to the first input of the comparator 180.

The second input of comparator 170 receives a sawtooth signal from a sawtooth generator 172. The comparator 170 compares the magnitudes of the signals received at the two inputs to output a pulse width modulation signal to the controller 180. The controller 180 controls the duty cycle of the on-time of the first high-order transistor switch 122 and the low-level transistor switch 124 according to the pulse width modulation signal to adjust the output current I _{L of the} entire circuit to a predetermined value.

In the present embodiment, the error signal selector 152 and the error signal selector 152 are connected to the voltage error amplifier 154 mainly in response to an output mode and a constant voltage output which are required to be applied to a constant current, such as a battery charger. Set to switch between working modes. Many types of rechargeable batteries have the following requirements: When the voltage of the rechargeable battery is lower than a certain value, the rechargeable battery is preferably charged with a constant current, and when the voltage of the rechargeable battery reaches or exceeds a certain value, the rechargeable battery is best. Accept constant voltage charging.

The error signal selector 152 can determine that the voltage of the rechargeable battery (ie, the external load 20) is lower or higher than a certain set voltage value (ie, a preset voltage threshold) according to the magnitude of the voltage error signal output by the voltage error amplifier 154. . When the error signal selector 152 determines that the voltage of the rechargeable battery is lower than the set voltage value, the error signal selector 152 selects the output current error signal to the comparator 170; at this time, the integrated circuit 100 operates in the output mode of the constant current, and Output via the power output contact 112 Current. When the error signal selector 152 determines that the voltage of the rechargeable battery is higher than the set voltage value, the error signal selector 152 selects the output voltage error signal to the comparator 170; at this time, the integrated circuit 100 operates in the constant voltage output mode, and via The power output contact 112 outputs a constant voltage.

In other words, when a switching power supply conversion circuit (or an integrated circuit having such a circuit) capable of a constant current output is applied to a case where only a constant current is required to output a constant voltage, a switching power supply conversion capable of a constant current output is possible. The circuit (or an integrated circuit having such a circuit) may not include a voltage feedback contact 115 (voltage feedback terminal), a feedback circuit 190, a voltage error amplifier 154, and an error signal selector 152. At this time, the output of the current error amplifier 150 is connected to the first output of the comparator 170.

Fig. 4 is a view showing a switching power supply switching circuit of a constant current output according to a second embodiment of the present invention.

Referring to FIG. 4, in this embodiment, the connection between the power conversion circuit 120 (ie, the high-level transistor switch 122 and the low-level transistor switch 124) and the external inductor 22, and their respective power input contacts 111, The connection manner of the power output contact 112 and the power negative contact 113 is different from that of the first embodiment shown in FIG. 3, but in the second embodiment shown in FIG. 4, the circuit layout of this portion is commonly used. The main circuit of the step-up switching power converter, that is, the switching power conversion circuit capable of constant current output can be a step-up switching power converter circuit. Moreover, the main circuit of the step-up switching power converter is well known in the prior art and is well known to those skilled in the art, and thus will not be described herein.

In this embodiment, the power conversion circuit 120 is arranged as a step-up switching power conversion circuit. Here, the anode of the lower transistor switch 124 of the power conversion circuit 120 is connected to the power input contact 111, and the external inductor 22 is connected between the power input V _IN and the power input contact 111. For the remaining circuit layout in the second embodiment shown in FIG. 4, please refer to the corresponding description of the first embodiment shown in FIG. 3 above.

Fig. 5 is a view showing a switching power supply switching circuit of a constant current output according to a third embodiment of the present invention.

Referring to FIG. 5, the power conversion circuit 120 includes two upper level transistor switches 122, 123 and two lower level transistor switches 124, 125. In this embodiment, the connection manner between the power conversion circuit 120 and the external inductor 22, and the manner in which they are connected to the power input contact 111, the power output contact 112, and the power negative contact 113, respectively.

The connection between the power conversion circuit 120 (ie, the high-level transistor switch 122 and the low-level transistor switch 124) and the external inductor 22, and their respective power input contacts 111, the power output contact 112, and the power negative contact 113 The connection mode belongs to the main circuit of the commonly used buck-boost switching power converter, that is, the switching power conversion circuit capable of constant current output can be a buck-boost switching power converter circuit. Moreover, the main circuit of the buck-boost switching power converter is well known in the prior art and is well known to those skilled in the art, and thus will not be described herein. In addition, the buck-boost switching power converter additionally needs to include a circuit for determining the timing of switching between the boost mode and the buck mode, and the circuit for controlling switching, since the circuit layout of this part is in the prior art. It is well known and well known to those skilled in the art, and thus will not be described again and is omitted in FIG.

In this embodiment, the power conversion circuit 120 is configured as a buck-boost power conversion circuit. Here, the positive electrode and the negative electrode of the high-position transistor switch 122 are respectively connected Connected to power input contact 111 and current output contact 116. The positive and negative poles of the high-position transistor switch 123 are connected to the current input contact 117 and the power supply output contact 112, respectively. The positive and negative poles of the lower transistor switch 124 are connected to the current output contact 116 and the power supply negative contact 113, respectively. The positive and negative poles of the lower transistor switch 125 are connected to the current input contact 117 and the power supply negative contact 113, respectively. The gates of the high level transistor switches 122, 123 are coupled to the high level signal output of the controller 180, and the gates of the low level transistor switches 124, 125 are coupled to the low level signal output of the controller 180. The first end of the external inductor 22 is connected to the current output contact 116, and the second end of the external inductor 22 is connected to the current input contact 117.

When the switching power conversion circuit of the constant current output is packaged into an integrated circuit 100, the current output contact 116 and the current input contact 117 are also external terminals of the integrated circuit 100. That is, the current output contact 116 and the current input contact 117 are the current output terminal and the current input terminal of the integrated circuit 100, respectively, and the external inductor 22 outside the integrated circuit 100 is connected across the current output terminal and the current input terminal. between.

For the remaining circuit layout in the third embodiment shown in FIG. 5, please also refer to the corresponding description of the first embodiment shown in FIG. 3 above.

In FIG. 5, for simplicity of illustration, the active shunt circuit 131 is represented by only an elliptical circle surrounding the current path of the high-position transistor switch 123. For the specific embodiment circuit, reference may be made to the first embodiment shown in FIG. Or the second embodiment shown in Fig. 4.

When the switchable power conversion circuit (or the integrated circuit 100 having the circuit) of the constant current output operates in the buck mode, the high-position transistor switch 123 and the sample/hold switch 142 remain normally open, and the low-position transistor switch 125 Then, the normally-off, sample/hold circuit 140 continues to maintain the sampling state and thus receives a complete output current I _L corresponding to the rising segment (the charging half cycle of the external inductor 22) and the falling segment (the discharge half cycle of the external inductor 22). Current sense voltage signal.

When the switchable power conversion circuit (or the integrated circuit 100 having the circuit) capable of constant current output operates in the boost mode, the high-position transistor switch 122 remains normally open, and the low-position transistor switch 124 remains normally closed; the high-position transistor The switch 123 and the low-position transistor switch 125 are alternately turned on and off at a high frequency, and the on-time (on-time) of the sample/hold switch 142 (i.e., the sampling period) is substantially synchronized with the on-time of the high-position transistor switch 123, so sampling/ The hold circuit 140 samples only the current signal when the external inductor 22 is discharged, that is, the falling segment signal of the output current I _L of the external inductor 22. Since the average value of the rising segment signal of the output current I _L of the external inductor 22 is equal to the average value of the falling segment signal, the falling segment signal of the output current I _L of the external inductor 22 sampled by the sample/hold circuit 140 can represent complete The signal of the output current I _L of the external inductor 22, and the signal is filtered by the resistor 145 and the holding capacitor 146, and output to the comparator 170 at the rear end to adjust the pulse width of the output pulse width modulation signal.

In the third embodiment shown in Fig. 5, although the active shunt circuit 131 is provided to monitor the current of the high-position transistor switch 123, the present invention is not limited thereto. For example, in other embodiments of the buck-boost switching power converter circuit, the active shunt circuit 131 can also be configured to monitor the current of the high-position transistor switch 122.

In summary, in the switching power conversion circuit capable of constant current output according to the present invention, the power conversion method thereof, and the manufacturing method of the integrated circuit having the same, In addition to the current output path (ie, the power conversion circuit 120), a current shunt path parallel to the current output path (particularly the active shunt circuit 131 parallel to the high-position transistor switch 122 or the high-position transistor switch 123) is provided. . The current flowing through the current shunt path is relatively small compared to the current flowing through the high-level transistor switch in the current output path and is proportional to both. In some embodiments, the second input of current error amplifier 150 is coupled to a voltage source (ie, signal generation circuit 160) that can be set by the user.

In operation, the current I _{S that} is forced to flow through the active shunt circuit 131 is a fixed fraction (ie, n-th) of the current I _M flowing through the high-level transistor switch in the current output path, so that it can be monitored. The amount of current I _S flowing through the active shunt circuit 131 calculates the amount of output current flowing through the high-level transistor switch. Further, in the same pulse period, the average value of the current I _M flowing through the upper transistor switch in the upper half cycle is substantially equal to the average value of the current flowing through the lower transistor switch in the lower half cycle. Therefore, the average output current amount of the entire circuit (or the integrated circuit 100) can be obtained by monitoring the average value of the current I _S flowing through the active shunt line 131 when the high-position transistor switch is turned on. Furthermore, after the current sensing voltage signal is filtered by the sample/hold circuit 140, the amplitude of the output current monitoring signal is reduced and approaches the average of the original potential difference. Because the voltage rise and fall rate of the signal output by the current error amplifier is lower than the voltage rise and fall rate of the input signal (ie, the bandwidth of the amplifier is lower than the input signal frequency), and is higher than the received frequency of the first input terminal. The frequency signal (current monitoring signal) is equivalent to a low-pass filter, so that the input current monitoring signal not only reduces the amplitude of the chopping but also effectively avoids the subharmonic oscillation.

Switched power conversion circuit capable of constant current output according to the present invention, and power supply thereof The conversion method and the manufacturing method of the integrated circuit having the same can be applied to, for example, a charger of a battery or a driver of a light-emitting diode, etc., where a fixed current is required to be output to an external load.

While the present invention has been described above in the foregoing embodiments, it is not intended to limit the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of patent protection shall be subject to the definition of the scope of the patent application attached to this specification.

10‧‧‧Switching Power Converter

10'‧‧‧Switching Power Converter

12‧‧‧ Controller

14‧‧‧Inductance

16‧‧‧ Capacitance

18‧‧‧ Current sense resistor

19‧‧‧Filter circuit

20‧‧‧ load

21‧‧‧Voltage detection point

22‧‧‧External inductance

24‧‧‧Output capacitor

26‧‧‧Set resistor

100‧‧‧ integrated circuit

111‧‧‧Power input contacts

112‧‧‧Power output contacts

113‧‧‧Power negative contact

114‧‧‧ Current setting contact

115‧‧‧Voltage feedback contact

116‧‧‧current output contacts

117‧‧‧current input contacts

120‧‧‧Power conversion circuit

122‧‧‧High-position transistor switch

123‧‧‧High-position transistor switch

124‧‧‧Low transistor switch

125‧‧‧Low transistor switch

130‧‧‧ Current sensing circuit

131‧‧‧Active shunt circuit

132‧‧‧High-position transistor switch

134‧‧‧potentiometric circuit

135‧‧‧ Current sense resistor

140‧‧‧Sampling/holding circuit

142‧‧‧Sampling/holding switch

144‧‧‧ low pass filter

145‧‧‧resistance

146‧‧‧Retaining capacitor

150‧‧‧ Current Error Amplifier

152‧‧‧Error signal selector

154‧‧‧Voltage error amplifier

160‧‧‧Signal generation circuit

162‧‧‧current voltage converter

163‧‧‧current voltage conversion resistor

164‧‧‧potentiometric circuit

170‧‧‧ comparator

172‧‧‧Sawtooth generator

180‧‧‧ Controller

190‧‧‧Return circuit

M _H ‧‧‧ high switching transistor

M _L ‧‧‧Low Transistor Switch

PIN‧‧‧Power input

PGND‧‧‧Power negative

V _R ‧‧‧potential difference

I _L ‧‧‧Output current

Rf‧‧‧Filter resistor

Cf‧‧‧Filter Capacitor

V _L ‧‧‧potential difference

V _IN ‧‧‧Power input

V _OUT ‧‧‧Power output

Iset‧‧‧Set current

V _FB ‧‧‧Response signal

OP1‧‧‧Operational Amplifier

OP2‧‧‧Operational Amplifier

M1‧‧‧O crystal

M2‧‧‧O crystal

I _S ‧‧‧ Current

I _M ‧‧‧current

Vset‧‧‧ reference set potential

Vref‧‧‧ voltage reference signal

Figure 1 is a circuit diagram of a buck-type constant current output switching power converter.

Figure 2 is a circuit diagram of another buck-type constant current output switching power converter.

Fig. 3 is a view showing a switching power supply switching circuit of a constant current output according to the first embodiment of the present invention.

Fig. 4 is a view showing a switching power supply switching circuit of a constant current output according to a second embodiment of the present invention.

Fig. 5 is a view showing a switching power supply switching circuit of a constant current output according to a third embodiment of the present invention.

20‧‧‧ load

21‧‧‧Voltage detection point

22‧‧‧External inductance

24‧‧‧Output capacitor

26‧‧‧Set resistor

100‧‧‧ integrated circuit

111‧‧‧Power input contacts

112‧‧‧Power output contacts

113‧‧‧Power negative contact

114‧‧‧ Current setting contact

115‧‧‧Voltage feedback contact

120‧‧‧Power conversion circuit

122‧‧‧High-position transistor switch

124‧‧‧Low transistor switch

130‧‧‧ Current sensing circuit

131‧‧‧Active shunt circuit

132‧‧‧High-position transistor switch

134‧‧‧potentiometric circuit

135‧‧‧ Current sense resistor

140‧‧‧Sampling/holding circuit

142‧‧‧Sampling/holding switch

144‧‧‧ low pass filter

145‧‧‧resistance

146‧‧‧Retaining capacitor

150‧‧‧ Current Error Amplifier

152‧‧‧Error signal selector

154‧‧‧Voltage error amplifier

160‧‧‧Signal generation circuit

162‧‧‧current voltage converter

163‧‧‧current voltage conversion resistor

164‧‧‧potentiometric circuit

170‧‧‧ comparator

172‧‧‧Sawtooth generator

180‧‧‧ Controller

190‧‧‧Return circuit

I _L ‧‧‧Output current

V _IN ‧‧‧Power input

V _OUT ‧‧‧Power output

Iset‧‧‧Set current

V _FB ‧‧‧Response signal

OP1‧‧‧Operational Amplifier

OP2‧‧‧Operational Amplifier

M1‧‧‧O crystal

M2‧‧‧O crystal

I _S ‧‧‧ Current

I _M ‧‧‧current

Vset‧‧‧ reference set potential

Vref‧‧‧ voltage reference signal

Claims (27)

A switching power conversion circuit capable of constant current output, comprising: a power input contact; a power output contact; a power conversion circuit electrically connected between the power input contact and the power output contact, The power conversion circuit includes a first high level transistor switch and a low level transistor switch, the first high level transistor switch and the low level transistor switch are alternately turned on according to a pulse width modulation signal; a current sensing circuit, a current sensing voltage signal for generating a current corresponding to the first high-position transistor switch; a sample/hold circuit for outputting a current monitoring signal according to the current sensing voltage signal during sampling, and during the holding period Outputting the current monitoring signal at a high level, wherein the sampling period of the sample/hold circuit is substantially synchronized with an on period of the first high level transistor switch; a signal generating circuit for generating a current reference voltage signal; a current error amplifier for outputting a current error signal according to the current monitoring signal and the current reference voltage signal ; And a comparator, the time for contact output to the power output of a constant current, the PWM signal is output to the current error signal according to a sawtooth signal. The switching power conversion circuit of claim 1, wherein the current sensing circuit comprises: a second high-level transistor switch, wherein the second high-level transistor switch has an on-resistance of the first high-level a fixed multiple of the on-resistance of the crystal switch; a first potential balancing circuit for forcibly maintaining the negative pole of the first high-position transistor switch and the anode potential of the second high-position transistor switch; and a current sensing resistor for receiving the second high-level power The current of the crystal switch generates the current sense voltage signal. The switchable power conversion circuit of claim 2, wherein the first potential balancing circuit comprises: an operational amplifier, the two input ends of the operational amplifier are respectively connected to the negative pole of the first high-position transistor switch and a negative electrode of the second high-position transistor switch; and a transistor having a control electrode connected to an output end of the operational amplifier, a positive electrode of the transistor connected to a negative electrode of the second high-position transistor switch, and a transistor The negative electrode is connected to the current sensing resistor. The switchable power conversion circuit of claim 1, wherein the sample/hold circuit comprises: a sample/hold switch for receiving the current sense voltage signal and outputting the current monitor signal, the sample And maintaining a conduction period of the switch substantially synchronous with an on period of the first high level transistor switch; and a low pass filter for filtering the current monitoring signal and outputting the filtered current monitoring signal to the current Error amplifier. The switching power conversion circuit of claim 1, wherein the power conversion circuit is a step-down switching power conversion circuit or a step-up switching power conversion circuit. The switching power conversion circuit of claim 1, wherein the power conversion circuit is a buck-boost switching power conversion circuit. The switching power conversion circuit of claim 1, wherein the first high level transistor switch and the low level transistor switch are metal oxide half field effect transistors. The switching power conversion circuit of any of the items 1 to 7, wherein the power input contact and the power output contact are external terminals of an integrated circuit, and the power conversion The circuit, the current sensing circuit, the sample/hold circuit, the signal generating circuit, the current error amplifier, and the comparator are disposed inside the integrated circuit. The switching power conversion circuit of the constant current output according to any one of claims 1 to 7, further comprising: a voltage error amplifier for electrically connecting the power output according to a voltage reference signal A voltage monitoring signal of a voltage of an external load outputs a voltage error signal; and an error signal selector for outputting the voltage error signal or the current error signal to the comparator according to the voltage of the external load. The switching power conversion circuit of claim 9, wherein the power input contact and the power output contact are external terminals of an integrated circuit, and the power conversion circuit and the current sensing circuit The sample/hold circuit, the signal generating circuit, the current error amplifier, the comparator, the voltage error amplifier, and the error signal selector are disposed inside the integrated circuit. The switchable power conversion circuit for determining the current output according to claim 10, further comprising: a current setting contact for receiving a set current, wherein the current setting The contact is the external terminal of the integrated circuit, and the set current is a fixed value; wherein the signal generating circuit comprises: a second potential balancing circuit for forcing the potential of the current setting terminal to be the same as a fixed potential; And a current-voltage converter for converting the set current into a voltage signal as the current reference voltage signal. The switching power conversion circuit of the current output according to claim 9 further comprising: a current setting contact for receiving a set current, wherein the set current is a fixed value; wherein the signal generating circuit comprises a second potential balancing circuit for forcing the potential of the current setting terminal to be the same as a fixed potential; and a current to voltage converter for converting the set current into a voltage signal as the current reference voltage signal. The switching power conversion circuit of the constant current output according to any one of claims 1 to 7, further comprising: a current setting contact for receiving a set current, wherein the set current is a fixed value; The current reference signal generating circuit includes: a second potential balancing circuit for forcing the potential of the current setting terminal to be the same as a fixed potential; and a current voltage converter for converting the set current into a voltage The signal acts as the current reference voltage signal. The switchable power conversion circuit of the current output according to any one of the preceding claims, wherein the power input contact, the power output contact, and the current setting contact are external terminals of an integrated circuit, And the power conversion circuit, the current sensing circuit, the sample/hold circuit, the signal generating circuit, the current error amplifier, and the comparator are disposed inside the integrated circuit. A method for manufacturing an integrated circuit includes: providing a power input terminal and a power output terminal on an integrated circuit; and electrically connecting the power input terminal and the power output terminal in the integrated circuit a power conversion circuit, wherein the power conversion circuit includes a high level transistor switch and a low level transistor switch alternately turned on according to a pulse width modulation signal; a current sensing circuit is disposed in the integrated circuit for When the high-position transistor switch is turned on, sensing a current flowing through the high-position transistor switch and outputting a current-sensing voltage signal; and setting a sample/hold circuit in the integrated circuit to sample the current-sensing voltage signal and outputting a signal a current monitoring signal and maintaining the current sensing voltage signal when the high level transistor switch is not conducting; a signal generating circuit is disposed in the integrated circuit to generate a current reference voltage signal; and a current is set in the integrated circuit An error amplifier for outputting a current error signal according to the current monitoring signal and the current reference voltage signal; a comparator is provided in the body circuit for outputting the contact output of the power source The pulse width modulation signal is output according to a sawtooth signal and the current error signal at a certain current. The method of manufacturing an integrated circuit according to claim 15, wherein the power conversion circuit is configured as a step-down switching power conversion circuit or a step-up switching power conversion circuit. The method of manufacturing an integrated circuit according to claim 15, wherein the power conversion circuit is a switch-type power conversion circuit that is arranged in a buck-boost type. The method for manufacturing an integrated circuit according to any one of claims 15 to 17, further comprising: providing a voltage error amplifier in an integrated circuit to electrically connect the voltage reference signal according to a voltage reference signal a voltage monitoring signal of a voltage of an external load of the power output contact outputs a voltage error signal; and an error signal selector is disposed in an integrated circuit to output the voltage error signal according to the voltage of the external load or The current error signal is applied to the comparator. The method of manufacturing the integrated circuit of claim 18, further comprising: providing a current setting terminal on the integrated circuit to receive a set current having a fixed value flowing from outside the integrated circuit; wherein The step of setting the signal generating circuit includes: setting a potential balancing circuit on the integrated circuit to force the potential of the current setting terminal to be the same as a fixed potential; and setting a current-voltage converter on the integrated circuit to The set current is converted into a voltage signal as the current reference voltage signal. The method of manufacturing an integrated circuit according to any one of claims 15 to 17, further comprising: providing a current setting terminal on the integrated circuit to receive a fixed value flowing from outside the integrated circuit a setting current; wherein the setting step of the signal generating circuit comprises: setting a potential balancing circuit on the integrated circuit to force the potential of the current setting terminal to be the same as a fixed potential; and setting a set on the integrated circuit A current-to-voltage converter converts the set current into a voltage signal as the current reference voltage signal. A switching power conversion method capable of constant current output, comprising: alternately conducting a first high level transistor switch and a low level transistor switch according to a pulse width modulation signal, wherein the first high level transistor switch is disposed in a a first current path between the power input contact and a power output contact, and the low level transistor switch is disposed between the power input contact and a power negative contact or the power output contact and the a second current path between the negative contacts of the power supply; sensing a current through the first high-position transistor switch to generate a current sense voltage signal corresponding to the current through the first high-position transistor switch; The current sensing voltage signal is sampled by a sample/hold switch during the on period of the first high level transistor switch to output a current monitoring signal according to the current sensing voltage signal; and utilized during the non-conduction of the first high level transistor switch The sample/hold switch maintains the current sense voltage signal to output the current monitor maintained at a high level Measuring a signal; outputting a current error signal according to the current monitoring signal and a current reference voltage signal; and outputting the pulse width modulation signal according to a sawtooth signal and the current error signal when the power output contact outputs a certain current. The switching power conversion method of claim 1, wherein the sensing step comprises: using the on-resistance as one of a fixed multiple of the on-resistance of the first high-position transistor switch; The switch generates a sense current corresponding to the current through the first high-position transistor switch; forcibly maintaining the negative pole of the first high-position transistor switch and the cathode potential of the second high-position transistor switch; and utilizing a current sense resistor The current sense voltage signal is generated based on the sense current. The switching power conversion method of the constant current output according to claim 22, further comprising: filtering the current monitoring signal before the outputting step of the current error signal. The switching power conversion method of the determinable current output according to claim 21, further comprising filtering the current monitoring signal before the outputting step of the current error signal. Switchable power for a constant current output according to any one of claims 21 to 24 The source conversion method further includes: outputting a voltage error signal according to a voltage reference signal and a voltage monitoring signal corresponding to a voltage of an external load electrically connected to the power output contact; and outputting the voltage according to the voltage of the external load A voltage error signal or the current error signal is applied to the comparator. The switching power conversion method of the constant current output according to claim 25, further comprising: receiving a set current having a fixed value via a current setting contact; forcing the potential of the current setting contact to be the same as a fixed potential; And converting the set current into a voltage signal as the current reference voltage signal. The switching power conversion method of the constant current output according to any one of claims 21 to 24, further comprising: receiving a set current having a fixed value via a current setting contact; forcing the current to set the contact The potential is the same as a fixed potential; and the set current is converted into a voltage signal as the current reference voltage signal.