TWI538370B - Power supply system, and method of and soft-start feedback circuitry for controlling switched-mode power supply circuitry to generate predefined dc output voltage during soft-start period of operation - Google Patents

Description

Power supply system and method for controlling a switched mode power supply circuit to generate a predefined DC output voltage during a soft start operating cycle and a soft start feedback circuit

The present invention relates to switched mode power supplies and, more particularly, to soft start control techniques for a switched mode power supply.

The features and advantages of the subject matter will be apparent from the following detailed description of the embodiments of the invention.

While the following detailed description is set forth with reference to the exemplary embodiments

In general, the present invention provides soft start control techniques for a power supply. These control techniques can be used to prevent saturation of the soft start feedback amplifier and maintain controllability of the feedback loop. In a feedback control technique, a voltage amplifier is used to generate a feedback control signal based on the output voltage of the power supply and a reference voltage to control the power supply. The reference voltage is generated using a controllable current source, and the output of the controllable current source is adaptively adjusted based on the output voltage of the power supply and the reference voltage. In another feedback control technique, a transconductance amplifier is used instead of a voltage amplifier. By controlling the input to the amplifier, the saturation of the error amplifier is avoided and the response time of the feedback loop is increased. For example, such techniques can achieve full control of the power supply output voltage during a soft start cycle to prevent one voltage drop when the power supply is loaded and prevent one output voltage overshoot at a lighter output load .

FIG. 1 illustrates a power supply system 100 in accordance with an embodiment of the present invention. The power supply system 100 of FIG. 1 includes a switching mode power supply Circuit 102, switched mode power supply circuit 102 is typically configured as a DC/DC converter to provide an output voltage (Vout) from an input voltage (Vin) to supply power to a load. The switched mode power supply circuit 102 can include a buck converter circuit, a boost converter circuit, a buck-boost converter circuit, a flyback converter circuit, a SEPIC converter circuit, etc., and/or any other known Switch mode power supply circuit topology developed later or later. The power supply system 100 also includes a soft start feedback circuit that is generally illustrated at 103. As is known, a soft start system actively controls the power supply to cause a rise in output voltage to occur at a relatively constant rate of processing when power is turned on. Thus, the soft start circuit 103 is configured to generate a control signal VCOMP based on the output voltage (VOUT) and a reference voltage, as will be explained in more detail below.

The soft start feedback circuit 103 includes a controllable current source circuit 104 and a voltage amplifier circuit 106 that are configured to generate a controllable current ISS. The voltage amplifier circuit 106 is configured to receive a feedback voltage (VFB) indicative of or proportional to the output voltage (VOUT) of the power supply circuit 102. For example, the soft start feedback circuit 103 can include a voltage divider circuit 107 coupled to a DC output voltage (VOUT) and configured to generate a feedback voltage (VFB). The amplifier circuit 106 is configured to compare the feedback voltage (VFB) with a reference voltage (VSS) generated by the current source circuit 104 via a soft start capacitor CSS and a Zener diode tied to a ground (or reference) potential. In this embodiment, the current ISS generated by current source circuit 104 is controlled by the feedback voltage (VFB) and reference voltage (VSS) depicted at summing node 108. In this example, VSS acts as a positive feedback control and VFB operates as a negative feedback control. Therefore, the increase of VFB Adding (indicating an increase in one of the output voltages VOUT) will cause the ISS and thus VSS to decrease to prevent saturation of the amplifier 106.

FIG. 2 illustrates a power supply system 200 in accordance with another embodiment of the present invention. The power supply system 200 of this embodiment is similar to the power supply system 100 of the previous embodiment, however, instead of voltage feedback control, the present embodiment uses current feedback control via a transconductance (gM) amplifier circuit 206. The soft start feedback circuit 203 includes a controllable current source circuit 204 and a current amplifier circuit 206 that are configured to generate a controllable current ISS. Current amplifier circuit 206 is configured to receive a feedback voltage (VFB) indicative of or proportional to an output voltage (VOUT) of power supply circuit 202. For example, the soft start feedback circuit 203 can include a voltage divider circuit 207 coupled to a DC output voltage (VOUT) and configured to generate a feedback voltage (VFB). The amplifier circuit 206 is configured to compare the feedback voltage (VFB) with a reference voltage (VSS) generated by the current source circuit 204 via a soft start capacitor CSS and a Zener diode tied to a ground (or reference) potential. In this embodiment, the current ISS generated by current source circuit 204 is controlled by the feedback voltage (VFB) and reference voltage (VSS) depicted at summing node 208. In this example, VSS acts as a positive feedback control and VFB operates as a negative feedback control. Therefore, an increase in VFB (indicating an increase in one of the output voltages VOUT) will cause the ISS and thus VSS to decrease to prevent saturation of the amplifier 206.

In any of the foregoing embodiments, the output of the amplifier, VCOMP, can be used to control the power supply circuit to adjust VOUT. For example, the power supply circuit 102/202 can include a pulse width modulation (PWM) circuit, and VCOMP can be used to adjust the duty cycle of the PWM signal to adjust delivery to The power of the load. In another example, power supply circuit 102/202 can include a pulse frequency modulation (PFM) circuit, and VCOMP can be used to adjust the pulse rate of the modulated signal to adjust the power delivered to the load.

FIG. 3 illustrates a voltage/current waveform 300 associated with operation of the amplifier circuit of the embodiment of FIGS. 1 and/or 2. In particular, waveform 300 illustrates soft start current ISS as a function of soft start voltage (VSS) and feedback voltage (VFB). As VSS-VFB increases, the value of ISS decreases so that the amplifier circuit operates in an unsaturated range. In this example, as VSS-VFB increases from 0 volts to 40 mV, the ISS decreases from 20 uA to 4 uA. Of course, these values are provided as an example and not as a limitation.

4 illustrates a timing diagram 400 of various signals associated with operation of the power supply system of FIGS. 1 and/or 2. Waveform 402 is the output voltage VOUT during one soft-start period of the power supply. Regardless of the load conditions, VOUT ramps up slowly and remains constant once the target voltage level is reached. Waveform 404 is a feedback voltage VFB and a soft start reference voltage VSS. In this example, the signals substantially coincide, indicating that the output voltage is tracking the reference voltage with a relatively high accuracy. Waveform 406 is VSS-VFB, which is the voltage at sum node 108/208. Waveform 408 is a control signal VCOMP generated by amplifier circuit 106/206. Waveform 410 is the ISS current and waveform 412 is the output current IOUT.

Figure 5 illustrates a comparative timing diagram of various signals associated with the operation of the power supply system of Figure 1 or Figure 2 as compared to a conventional open loop soft start control technique. Waveform 502 illustrates the output voltage (VOUT2) of the open loop soft start control and uses the closed loop control technique illustrated in FIG. 1 and/or FIG. VOUT. Note that VOUT2 is greater than VOUT, which indicates that the open loop control can have an output voltage overshoot. Waveform 504 illustrates the output of error amplifier 106/108, which indicates that the output operates in a relatively small voltage range (approximately 0 volts to 2 volts), as opposed to waveform 506, which is depicted in an open loop control technique. The output of one of the amplifiers is used, where the operating voltage range is much larger (eg, 0 volts to 4 volts). Operating an amplifier in the range depicted in waveform 506 can indicate saturation of the amplifier, which reduces the controllability of the power supply system.

As used in any embodiment herein, the term "circuitry or circuit" may include, for example, hardwired circuitry, programmable circuitry, state machine circuitry, in a single form or in any combination. And/or circuitry included in a larger system (for example, an element that can be included in an integrated circuit).

The terms and expressions used herein are used to describe and not to limit the terms, and the use of such terms and expressions is not intended to exclude any equivalents of the features shown and described. It will be appreciated that various modifications may be made within the scope of the patent application. Therefore, the scope of the patent application is intended to cover all such equivalents. Various features, aspects, and embodiments have been set forth herein. The features, aspects, and embodiments are susceptible to being combined with each other and are susceptible to variations and modifications, as will be understood by those skilled in the art. Accordingly, the invention is considered to be inclusive of such combinations, variations and modifications.

100‧‧‧Power supply system

102‧‧‧Switch mode power supply circuit / power supply circuit

103‧‧‧Soft start feedback circuit / soft start circuit

104‧‧‧Controllable current source circuit/current source circuit

106‧‧‧Voltage Amplifier Circuit / Amplifier Circuit / Amplifier / Error Amplifier

107‧‧‧ Divider circuit

108‧‧‧To sum node/error amplifier

200‧‧‧Power supply system

202‧‧‧Power supply circuit

203‧‧‧Soft start feedback circuit

204‧‧‧Controllable current source circuit/current source circuit

206‧‧‧Transconductance (gM) amplifier circuit / current amplifier circuit / amplifier circuit / amplifier

207‧‧‧ voltage divider circuit

208‧‧‧ seeking sum node

300‧‧‧Voltage/current waveform/waveform

400‧‧‧ Timing diagram

402‧‧‧ waveform

404‧‧‧ waveform

406‧‧‧ waveform

408‧‧‧ waveform

410‧‧‧ waveform

412‧‧‧ waveform

502‧‧‧ waveform

504‧‧‧ waveform

506‧‧‧ waveform

C _SS ‧‧‧Soft Start Capacitor

I _OUT ‧‧‧Output current

I _SS ‧‧‧Controllable current/current/soft start current

V _COMP ‧‧‧Control signal/output

V _FB ‧‧‧ feedback voltage

V _IN ‧‧‧ input voltage

V _OUT ‧‧‧ output voltage

V _SS ‧‧‧reference voltage / soft start voltage / soft start reference voltage

Vout2‧‧‧ output voltage

1 illustrates a power supply system in accordance with an embodiment of the present invention. Figure 2 illustrates a power supply system in accordance with another embodiment of the present invention; Figure 3 illustrates a voltage/current waveform associated with operation of the amplifier of the embodiment of Figure 1 or Figure 2; Figure 4 illustrates FIG. 1 or FIG. 2 is a timing diagram of various signals related to the operation of the power supply system; and FIG. 5 illustrates the operation of the power supply system of FIG. 1 or FIG. 2 in comparison with a conventional open loop soft start control technique. Comparative timing diagram of various signals.

100‧‧‧Power supply system

102‧‧‧Switch mode power supply circuit / power supply circuit

103‧‧‧Soft start feedback circuit / soft start circuit

104‧‧‧Controllable current source circuit/current source circuit

106‧‧‧Voltage Amplifier Circuit / Amplifier Circuit / Amplifier / Error Amplifier

107‧‧‧ Divider circuit

108‧‧‧To sum node/error amplifier

C _SS ‧‧‧Soft Start Capacitor

I _SS ‧‧‧Controllable current/current/soft start current

V _COMP ‧‧‧Control signal/output

V _FB ‧‧‧ feedback voltage

V _IN ‧‧‧ input voltage

V _OUT ‧‧‧ output voltage

V _SS ‧‧‧reference voltage / soft start voltage / soft start reference voltage

Claims (20)

A power supply system includes: a switched mode power supply circuit configured to generate a DC output voltage from a DC input voltage; a soft start feedback circuit configured to control the switching during a soft start operating cycle a mode power supply circuit to generate a predefined output voltage, the soft start feedback circuit comprising: a controllable current source configured to generate a reference current and a reference voltage, wherein the reference current is based on the reference voltage and sum The output voltage is proportional to a difference between the feedback voltages; and an amplifier circuit configured to compare the feedback voltage to the reference voltage and generate a control signal to control the switching mode power supply during the soft start operation period Supply operation. A power supply system as claimed in claim 1, wherein the amplifier circuit comprises a voltage amplifier circuit. A power supply system as claimed in claim 1, wherein the amplifier circuit comprises a current amplifier circuit. A power supply system as claimed in claim 3, wherein the current amplifier circuit comprises a transconductance (gM) amplifier circuit. A power supply system as claimed in claim 1, wherein the soft start feedback circuit further comprises a voltage divider circuit coupled to the DC output voltage and configured to generate the feedback voltage. The power supply system of claim 1, wherein the soft start feedback circuit further comprises a soft start capacitor coupled to the controllable current source, wherein the reference voltage is based on a voltage of the soft start capacitor. The power supply system of claim 1, wherein the reference voltage operates as a positive feedback control and the feedback voltage operates as a negative feedback control such that an increase in one of the feedback voltages causes the reference voltage to decrease. A method of controlling a switched mode power supply circuit to generate a predefined DC output voltage during a soft start operating cycle, the method comprising: generating a reference current and a reference voltage, wherein the reference current is based on the reference voltage Comparing the feedback voltage with a difference between one of the feedback voltages; comparing the feedback voltage with the reference voltage to generate a control signal to control operation of the switched mode power supply during a soft start operating cycle; and controlling based on the control signal The switched mode power supply circuit generates the predefined output voltage from a DC input voltage. The method of claim 8, wherein the feedback voltage is compared to the reference voltage using a voltage amplifier circuit. The method of claim 8, wherein the feedback voltage is compared to the reference voltage using a current amplifier circuit. The method of claim 10, wherein the current amplifier circuit comprises a transconductance (gM) amplifier circuit. The method of claim 8, wherein the feedback voltage is generated using a voltage divider circuit coupled to the DC output voltage. The method of claim 8, wherein the reference current and the reference voltage are generated by a controllable current source. The method of claim 13, wherein the reference voltage is based on coupling to the Control the voltage of one of the soft-start capacitors of the current source. The method of claim 8, wherein the reference voltage operates as a positive feedback control and the feedback voltage operates as a negative feedback control such that an increase in one of the feedback voltages causes the reference voltage to decrease. A soft start feedback circuit for controlling a switched mode power supply circuit to generate a predefined DC output voltage during a soft start operating cycle, the soft start feedback circuit comprising: a controllable current source configured to generate a a reference current and a reference voltage, wherein the reference current is based on a difference between the reference voltage and a feedback voltage that is proportional to the output voltage; and an amplifier circuit configured to compare the feedback voltage to the reference voltage And generating a control signal to control the operation of the switched mode power supply during the soft start operating cycle. A soft start feedback circuit as claimed in claim 16, wherein the amplifier circuit comprises a voltage amplifier circuit. A soft start feedback circuit as claimed in claim 16, wherein the amplifier circuit comprises a current amplifier circuit. The soft start feedback circuit of claim 16, wherein the soft start feedback circuit further comprises a voltage divider circuit coupled to the DC output voltage and configured to generate the feedback voltage. The soft start feedback circuit of claim 16, wherein the soft start feedback circuit further comprises a soft start capacitor coupled to the controllable current source, wherein the reference voltage is based on a voltage of the soft start capacitor.