Control device for use with switching converters
The present application provides a control device for controlling a switching converting module to generate an output signal of constant output current from a rectified AC power supply signal. The switching converting module comprises a primary winding for receiving the rectified AC power supply signal and a power switch coupled in series with the primary winding. The control device comprises: an AGC amplifier configured to receive a first sampling signal sampled from the rectified AC power supply signal, and to generate a reference signal of constant amplitude according to the first sampling signal; a signal comparator configured to compare the reference signal with a current sensing signal in proportion to a primary side current flowing through the primary side winding to generate a comparison signal; a signal generator configured to receive a second sampling signal sampled from the output signal, and to generate a clock signal according to the second sampling signal; and a control logic configured to generate a control signal for switching the power switch according to the comparison signal and the clock signal.
1. A control device for controlling a switching converting module to generate an output signal of constant output current from a rectified AC power supply signal, the switching converting module comprising a primary winding for receiving the rectified AC power supply signal and a power switch coupled in series with the primary winding, wherein the control device comprises:
an AGC amplifier configured to receive a first sampling signal sampled from the rectified AC power supply signal, and to generate a reference signal of constant amplitude according to the first sampling signal;
a signal comparator configured to compare the reference signal with a current sensing signal in proportion to a primary side current flowing through the primary side winding to generate a comparison signal;
a signal generator configured to receive a second sampling signal sampled from the output signal, and to generate a clock signal according to the second sampling signal; and
a control logic configured to generate a control signal for switching the power switch according to the comparison signal and the clock signal;
wherein the AGC amplifier comprises:
a first amplifier having a positive input node for receiving the first sampling signal, a negative input node coupled to ground via a resistor, and an output node coupled to the negative input node via a varistor;
a first comparator having a negative input node coupled to the output node of the first amplifier, a positive input node coupled to a first reference voltage, and an output node; and
a counter having an input node coupled to the output node of the first comparator, and an output node coupled to a control node of the varistor to adjust the resistance of the varistor.
2. The control device of claim 1 , wherein the signal generator comprises:
a current mirror having an input path for receiving an input current associated with the second sampling signal, and an output path for outputting a mirror current to a capacitor, wherein the capacitor is in parallel with an output switch;
a comparator having a positive input node for receiving the voltage across the capacitor, a negative input node for receiving a second reference voltage, and an output node coupled to a control node of the output switch and configured to output the clock signal.
3. The control device of claim 1 , wherein the control logic comprises a trigger.
4. The control device of claim 3 , wherein the control logic comprises a RS trigger having a reset node coupled to receive the comparison signal, a set node coupled to receive the clock signal, and an output node for outputting the control signal.
5. The control device of claim 1 , further comprising:
a first voltage divider configured to sample the rectified AC power supply signal to generate the first sampling signal.
6. The control device of claim 1 , wherein the switching converting module further comprises an auxiliary winding, the control device further comprises:
a second voltage divider configured to sample the output signal via the auxiliary winding to generate the second sampling signal.
7. A converter, comprising:
a switching converting module; and
a control device for controlling the switching converting module to generate an output signal of constant output current from a rectified AC power supply signal, the switching converting module comprising a primary winding for receiving the rectified AC power supply signal and a power switch coupled in series with the primary winding, wherein the control device comprises:
an AGC amplifier configured to receive a first sampling signal sampled from the rectified AC power supply signal, and to generate a reference signal of constant amplitude according to the first sampling signal;
a signal comparator configured to compare the reference signal with a current sensing signal in proportion to a primary side current flowing through the primary side winding to generate a comparison signal;
a signal generator configured to receive a second sampling signal sampled from the output signal, and to generate a clock signal according to the second sampling signal; and
a control logic configured to generate a control signal for switching the power switch according to the comparison signal and the clock signal;
wherein the AGC amplifier comprises:
a first amplifier having a positive input node for receiving the first sampling signal, a negative input node coupled to ground via a resistor, and an output node coupled to the negative input node via a varistor;
a first comparator having a negative input node coupled to the output node of the first amplifier, a positive input node coupled to a first reference voltage, and an output node; and
a counter having an input node coupled to the output node of the first comparator, and an output node coupled to a control node of the varistor to adjust the resistance of the varistor.
8. The converter of claim 7 , wherein the signal generator comprises:
a current mirror having an input path for receiving an input current associated with the second sampling signal, and an output path for outputting a mirror current to a capacitor, wherein the capacitor is in parallel with an output switch;
a comparator having a positive input node for receiving the voltage across the capacitor, a negative input node for receiving a second reference voltage, and an output node coupled to a control node of the output switch and configured to output the clock signal.
9. The converter of claim 7 , wherein the control logic comprises a trigger.
10. The converter of claim 9 , wherein the control logic comprises a RS trigger having a reset node coupled to receive the comparison signal, a set node coupled to receive the clock signal, and an output node for outputting the control signal.
11. The converter of claim 7 , further comprising:
a first voltage divider configured to sample the rectified AC power supply signal to generate the first sampling signal.
12. The converter of claim 7 , wherein the switching converting module further comprises an auxiliary winding, the control device further comprises:
a second voltage divider configured to sample the output signal via the auxiliary winding to generate the second sampling signal.
13. The converter of claim 7 , wherein the switching converting module is a fly-back converting module having a secondary winding for outputting the output signal.
14. The converter of claim 7 , wherein the switching converting module is a buck-boost converting module whose primary winding is further configured to output the output signal.