Control circuit of cascade type buck-boost converter and control method thereof

[0017] Such as figure 2 As shown, the cascaded buck-boost converter and its control circuit principle diagram involved in the embodiment of the present invention.

[0018] figure 2 The main circuit topology 10 of the medium cascade buck-boost converter includes a DC power supply V in , Four power switches Q 1 , Q 2 , Q 3 And Q 4 , Two inductors L 1 And L 2 , Two filter capacitors C 1 And C 2 , Resistance R o , Where: DC power supply V in Positive connection inductance L 1 One end, inductance L 1 The other end is connected to the power switch Q 1 Drain and power switch Q 2 The source of the power switch Q 2 The drains are connected to the filter capacitor C 1 One end of the power switch tube Q 3 Drain, power switch Q 3 The source is connected to the inductor L 2 One end of the power switch tube Q 4 Drain, inductance L 2 The other end is connected to the filter capacitor C 2 One end and resistance R o One end of the power switch tube Q 1 Source, filter capacitor C 1 The other end of the power switch Q 4 Source, filter capacitor C 2 The other end and resistance R o The other ends are connected to the DC power supply V in The negative electrode. In the figure, 101 is a boost converter circuit, and 102 is a buck converter circuit. In this circuit, the power switch tubes are all N-type metal oxide semiconductor field effect transistors (N-MOSFET), the inductor is wound with a magnetic powder core, and the filter capacitor is a multilayer ceramic capacitor (MLCC).

[0019] figure 2 The control circuit 20 of the intermediate cascade buck-boost converter includes an output voltage sampling circuit 206, a first error amplifier 201, a second error amplifier 202, a triangle wave generating circuit 203, a comparator circuit 207, a driving circuit 208, and a voltage setting circuit 205, where: the output voltage sampling circuit 206 includes a first voltage divider resistor R 23 And the second divider resistor R 24 , The first voltage divider resistor R 23One end of is connected to the output voltage V of the cascaded buck-boost converter circuit o The other end is connected to the inverting input end of the first error amplifier 201 and the second error amplifier 202 and the second voltage divider resistor R 24 One end, the second voltage divider resistor R 24 The other end of the first error amplifier 201 and the non-inverting input end of the second error amplifier 202 are both connected to the reference voltage V ref The comparator circuit 207 includes a first comparator 209, a second comparator 210, a first inverter 211 and a second inverter 212, the output of the first error amplifier 201 is connected to the non-inverting input of the first comparator 209 , The first control signal V output by the first comparator 209 cd1 As the first power switch Q 1 The control voltage is connected to the input terminal of the driving circuit 208, the output terminal of the first comparator 209 is connected to the input terminal of the first inverter 211, and the second control signal V output by the first inverter 211 cd2 As the second power switch Q 2 The control voltage is connected to the input terminal of the driving circuit 208, the output terminal of the second error amplifier 202 is connected to the non-inverting input terminal of the second comparator 210, and the third control signal V output by the second comparator 210 cd3 As the third power switch Q 3 The control voltage is connected to the input terminal of the driving circuit 208, the output terminal of the second comparator 210 is connected to the input terminal of the second inverter 212, and the fourth control signal V output by the second inverter 212 cd4 As the fourth power switch Q 4 The control voltage is connected to the input terminal of the driving circuit 208. The inverting input terminal of the first comparator 209 and the inverting input terminal of the second comparator 210 are both connected to the output terminal of the triangle wave generating circuit 203; the driving circuit 208 outputs the first Power switch Q 1 The driving voltage V d1 , The second power switch Q 2 The driving voltage V d2 , The third power switch Q 3 The driving voltage V d3 And the fourth power switch Q 4 The driving voltage V d4; Voltage setting circuit 205 includes a first diode D 21 , The second diode D 22 , The first resistance R 21 , The second resistor R 22 And capacitance C 21 , The first diode D 21 The anode is connected to the output terminal of the first comparator 209, the first diode D 21 The cathode is connected to the first resistor R 21 One end, the first resistance R 21 Connect the capacitor C to the other end 21 One end of the second resistor R 22 One end and the second diode D 22 Anode, capacitance C 21 The other end is connected to the second resistor R 22 The other end is connected to ground, and the second diode D 22 The cathode of is connected to the output terminal of the second error amplifier 202.

[0020] The key of this control circuit is the voltage setting circuit 205, the first diode D in the voltage setting circuit 205 21 And the first resistor R 21 The function is to prevent the capacitance C 21 The voltage on the first control signal V cd1 Have an impact, the first control signal V cd1 For a pulse width modulation voltage signal with a certain amplitude, the second diode D 22 And the second resistor R 22 The effect is that when the capacitor C 21 The voltage on the voltage drops to less than the second control voltage V c2 , Prevent the voltage from affecting the second control voltage V c2 Make an impact.

[0021] The control method of the cascaded buck-boost converter control circuit is: the first voltage divider resistor R in the output voltage sampling circuit 206 23 And the second divider resistor R 24 Through the output voltage V o Perform voltage division sampling to get the feedback voltage V fb , The first error amplifier 201 and the second error amplifier 202 are based on the feedback voltage V fb And reference voltage V ref The errors between correspond to the output first control voltage V c1 And the second control voltage V c2 , Feedback voltage V fb And output voltage V o Proportional; the first control voltage V c1 With triangle wave voltage V tri The first control signal V obtained by comparison cd1 And the second control signal V cd2 The first power switch tube Q is controlled by the driving circuit 208 1 And the second power switch Q 2 Action: When the first control voltage V c1 Greater than triangle wave voltage V tri 时,The first control signal V cd1 Is a positive voltage, the second control signal V cd2 Is zero, the first power switch Q 1 On, the second power switch tube Q 2 Turn off, when the first control voltage V c1 Less than triangle wave voltage V tri 时,The first control signal V cd1 Is zero, the second control signal V cd2 Is a positive voltage, the first power switch Q 1 Turn off, the second power switch tube Q 2 On, the first power switch tube Q 1 And the second power switch Q 2 Complementary conduction; first control signal V cd1 The second control voltage V is set by the voltage setting circuit 205 c2;The second control voltage V c2 With triangle wave voltage V tri The third control signal V obtained by comparison cd3 And the fourth control signal V cd4 The third power switch tube Q is controlled by the driving circuit 208 3 And the fourth power switch Q 4 Action: When the second control voltage V c2 Greater than triangle wave voltage V tri When, the third control signal V cd3 Is a positive voltage, the fourth control signal V cd4 Is zero, the third power switch Q 3 On, the fourth power switch tube Q 3 Turn off, when the second control voltage V c2 Less than triangle wave voltage V tri When, the third control signal V cd3 Is zero, the fourth control signal V cd4 Is a positive voltage, the third power switch tube Q 3 Turn off, the fourth power switch tube Q 3 On, the third power switch tube Q 3 And the fourth power switch Q 4 Complementary conduction.

[0022] The input terminal of the voltage setting circuit 205 can be connected as the first power switch Q 1 The first control signal V of the control voltage cd1 It can also be connected to the first power switch Q 1 The driving voltage V d1 , The first resistance R 21 With the first resistor R 21 The positions can be interchanged.

[0023] The specific working principle of the control circuit of the present invention is as follows:

[0024] When DC power supply V in The voltage is less than the output voltage V o When the first voltage error amplifier 201 outputs the first control voltage V c1 Greater than triangle wave voltage V tri To control the first power switch Q 1 And the second power switch Q 2 Action, the first control signal V cd1 The average value in one switching period is greater than zero, and the second control voltage V is made by the voltage setting circuit 205 c2 The minimum value in a switching cycle is greater than or equal to the triangular wave voltage V tri To control the third power switch Q 3 Always on, the fourth power switch tube Q 4 Always off, the converter works in boost mode. In this mode, the first error amplifier 201 plays a role of regulation and the second error amplifier 202 does not. When the DC power supply V in The voltage is greater than or equal to the output voltage V o , The first control voltage V output by the first error amplifier 201 c1 Less than triangle wave voltage V tri The minimum value of the first control signal V cd1 Always equal to zero, thus controlling the first power switch Q 1 Always off, the second power switch Q 2 Always on, the voltage setting circuit 205 does not work, and the second control voltage V c2 No effect, the second control voltage V output by the second error amplifier 202 c2 Less than or equal to triangle wave voltage V tri The maximum value of the second control voltage V c2 With triangle wave voltage V tri The third control signal V obtained by comparison cd3 And the fourth control signal V cd4 Control the third power switch Q respectively 3 And the fourth power switch Q 4 Action, the converter works in the step-down mode, in this mode, the second error amplifier 202 plays a role of regulation and the first error amplifier 201 does not play a role of regulation.