DC-DC converter and control circuit for DC-DC converter
View Patent ↗A control circuit for a DC-DC converter that prevents erroneous operations during high ON-duty operation. In response to an H-level pulse signal, a random delay circuit generates a delayed pulse signal that rises to an H level within one cycle of the pulse signal. The random delay circuit randomly changes the delay time of the delayed pulse signal. Even if noise causes the timing at which a current comparison signal rises to an H level to be delayed to later than the timing at which an H-level pulse signal is provided to the set terminal of an FF circuit, the FF circuit receives at its reset terminal an H-level delayed pulse signal that is provided prior to the H-level pulse signal. The FF circuit then inactivates the output transistor.
1. A DC-DC converter comprising:
a converter unit including an output transistor, of which activation and inactivation of the output transistor are controlled in accordance with a control signal, for generating output voltage of the DC-DC converter; and
a control unit, connected to the converter unit, for generating the control signal that controls the activation and inactivation of the output transistor, in which the control signal has a duty, in which the control unit changes the duty of the control signal based on output current corresponding to the output voltage, the control unit including;
a current detection circuit, connected to the converter unit, for detecting the output current and generating a detection signal;
an oscillator for generating a pulse signal;
a delay circuit, connected to the oscillator, for delaying the pulse signal and generating a delayed pulse signal, the delay circuit changing the delay time of the pulse signal; and
a flip-flop circuit having a set terminal, for receiving the pulse signal of the oscillator, and a reset terminal, for receiving the earlier one of the detection signal of the current detection circuit and the delayed pulse signal, wherein the flip-flop circuit generates the control signal with the duty in accordance with the pulse signal provided to the set terminal and the signal provided to the reset terminal.
2. The DC-DC converter according to claim 1 , wherein the delay circuit randomly changes the delay time.
3. The DC-DC converter according to claim 1 , further comprising:
a logic circuit, connected to the current detection circuit, the delay circuit, and the flip-flop circuit, for receiving the detection signal and the delayed pulse signal and providing the earlier one of the detection signal and the delayed pulse signal to the flip-flop circuit.
4. The DC-DC converter according to claim 1 , wherein:
the control unit includes a voltage detection circuit for detecting the output voltage of the DC-DC converter and generating a voltage detection signal; and
the delay circuit includes a plurality of delay circuits, each randomly changing the delay time of the pulse signal within different predetermined delay time ranges, and selects a delayed pulse signal generated by one of the delay circuits in accordance with the voltage detection signal of the voltage detection circuit.
5. The DC-DC converter according to claim 4 , wherein:
the voltage detection circuit compares the output voltage of the DC-DC converter with a reference voltage and generates a voltage detection signal that is in accordance with the result of the comparison; and
the delay circuit selects the delayed pulse signal generated by one of the delay circuits so as to decrease the ON duty of the output transistor and lower the output voltage when the output voltage is higher than the reference voltage in accordance with the voltage detection signal, and the delay circuit selects the delayed pulse signal generated by another one of the delay circuits to increase the ON duty of the output transistor and raise the output voltage when the output voltage is lower than the reference voltage.
6. A DC-DC converter comprising:
a converter unit including an output transistor, of which activation and inactivation of the output transistor are controlled in accordance with a control signal, for generating output voltage of the DC-DC converter; and
a control unit, connected to the converter unit, for generating the control signal that controls the activation and inactivation of the output transistor, in which the control signal has a duty, in which the control unit changes the duty of the control signal based on output current corresponding to the output voltage, the control unit including;
a current detection circuit, connected to the converter unit, for detecting the output current and generating a detection signal;
an oscillator for generating a pulse signal;
a delay circuit, connected to the oscillator, for delaying the pulse signal and generating a delayed pulse signal, the delay circuit changing the delay time of the pulse signal; and
a flip-flop circuit having a set terminal, for receiving the delayed pulse signal, and a reset terminal, for receiving the earlier one of the detection signal of the current detection circuit and the pulse signal of the oscillator, wherein the flip-flop circuit generates the control signal with the duty in accordance with the delayed pulse signal provided to the set terminal and the signal provided to the reset terminal.
7. The DC-DC converter according to claim 6 , wherein the delay circuit includes:
a plurality of delay circuits for receiving the pulse signal and generating a plurality of delayed pulse signals having different delay times;
a random circuit for generating a random signal; and
a selection circuit, connected to the delay circuits and the random circuit, for selectively outputting the delayed pulse signals using the random signal.
8. The DC-DC converter according to claim 6 , wherein:
the control unit includes a voltage detection circuit for detecting the output voltage of the DC-DC converter and generating a voltage detection signal; and
the delay circuit includes:
a plurality of delay circuits for receiving the pulse signal and generating a plurality of delayed pulse signals having different delay times, each delay circuit generating a plurality of delayed internal pulse signals and selecting one of the delayed internal pulse signals as the delayed pulse signal in accordance with the voltage detection signal;
a random circuit for generating a random signal; and
a selection circuit, connected to the delay circuits and the random circuit, for selectively outputting the delayed pulse signals using the random signal.
9. The DC-DC converter according to claim 8 , wherein:
the voltage detection circuit compares the output voltage of the DC-DC converter with the reference voltage and generates a voltage detection signal in accordance with the result of the comparison; and
each of the delay circuits selects one of the delayed internal pulse signals so as to decrease the ON duty of the output transistor and lower the output voltage when the output voltage is higher than the reference voltage according to the voltage detection signal, and each of the delay circuits selects another one of the delayed internal pulse signals so as to increase the ON duty of the output transistor and raise the output voltage when the output voltage is lower than the reference voltage.
10. The DC-DC converter according to claim 8 , wherein each of the delay circuits includes:
a plurality of series-connected delay circuits for generating the delayed internal pulse signal at the respective output terminals; and
a selection circuit, connected to the delay circuits, for receiving the delayed internal pulse signals from the delay circuits and selecting one of the delayed internal pulse signals in accordance with the voltage detection signal.
11. A control circuit for generating a control signal for controlling activation and inactivation of an output transistor of a converter unit that generates output voltage of a DC-DC converter, in which the control signal has a duty, and the control circuit changes the duty of the control signal based on output current corresponding to the output voltage, the control circuit comprising:
a current detection circuit, connected to the converter unit, for detecting the output current and generating a detection signal;
an oscillator for generating a pulse signal;
a delay circuit, connected to the oscillator, for delaying the pulse signal and generating a delayed pulse signal, the delay circuit changing the delay time of the pulse signal; and
a flip-flop circuit having a set terminal, for receiving the pulse signal of the oscillator, and a reset terminal, for receiving the earlier one of the detection signal of the current detection circuit and the delayed pulse signal, wherein the flip-flop circuit generates the control signal with the duty in accordance with the pulse signal provided to the set terminal and the signal provided to the reset terminal.
12. The control circuit according to claim 11 , wherein the delay circuit randomly changes the delay time.
13. The control circuit according to claim 11 , further comprising:
a logic circuit, connected to the current detection circuit, the delay circuit, and the flip-flop circuit, for receiving the detection signal and the delayed pulse signal and providing the earlier one of the detection signal and the delayed pulse signal to the flip-flop circuit.
14. The control circuit according to claim 11 , further comprising a voltage detection circuit for detecting the output voltage of the DC-DC converter and generating a voltage detection signal, wherein the delay circuit includes a plurality of delay circuits, each randomly changing the delay time of the pulse signal within different predetermined delay time ranges, and selects a delayed pulse signal generated by one of the delay circuits in accordance with the voltage detection signal of the voltage detection circuit.
15. The control circuit according to claim 14 , wherein:
the voltage detection circuit compares the output voltage of the DC-DC converter with a reference voltage and generates a voltage detection signal that is in accordance with the result of the comparison; and
the delay circuit selects the delayed pulse signal generated by one of the delay circuits so as to decrease the ON duty of the output transistor and lower the output voltage when the output voltage is higher than the reference voltage in accordance with the voltage detection signal, and the delay circuit selects the delayed pulse signal generated by another one of the delay circuits to increase the ON duty of the output transistor and raise the output voltage when the output voltage is lower than the reference voltage.
16. A control circuit for generating a control signal for controlling activation and inactivation of an output transistor of a converter unit that generates output voltage of a DC-DC converter, in which the control signal has a duty, and the control circuit changes the duty of the control signal based on output current corresponding to the output voltage, the control circuit comprising:
a current detection circuit, connected to the converter unit, for detecting the output current and generating a detection signal;
an oscillator for generating a pulse signal;
a delay circuit, connected to the oscillator, for delaying the pulse signal and generating a delayed pulse signal, the delay circuit changing the delay time of the pulse signal; and
a flip-flop circuit having a set terminal, for receiving the delayed pulse signal, and a reset terminal, for receiving the earlier one of the detection signal of the current detection circuit and the pulse signal of the oscillator, wherein the flip-flop circuit generates the control signal with the duty in accordance with the delayed pulse signal provided to the set terminal and the signal provided to the reset terminal.
17. The control circuit according to claim 16 , wherein the delay circuit includes:
a plurality of delay circuits for receiving the pulse signal and generating a plurality of delayed pulse signals having different delay times;
a random circuit for generating a random signal; and
a selection circuit, connected to the delay circuits and the random circuit, for selectively outputting the delayed pulse signals using the random signal.
18. The control circuit according to claim 16 , further comprising a voltage detection circuit for detecting the output voltage of the DC-DC converter and generating a voltage detection signal, wherein the delay circuit includes:
a plurality of delay circuits for receiving the pulse signal and generating a plurality of delayed pulse signals having different delay times, each delay circuit generating a plurality of delayed internal pulse signals and selecting one of the delayed internal pulse signals as the delayed pulse signal in accordance with the voltage detection signal;
a random circuit for generating a random signal; and
a selection circuit, connected to the delay circuits and the random circuit, for selectively outputting the delayed pulse signals using the random signal.
19. The control circuit according to claim 18 , wherein:
the voltage detection circuit compares the output voltage of the DC-DC converter with the reference voltage and generates a voltage detection signal in accordance with the result of the comparison; and
each of the delay circuits selects one of the delayed internal pulse signals so as to decrease the ON duty of the output transistor and lower the output voltage when the output voltage is higher than the reference voltage according to the voltage detection signal, and each of the delay circuits selects another one of the delayed internal pulse signals so as to increase the ON duty of the output transistor and raise the output voltage when the output voltage is lower than the reference voltage.
20. The control circuit according to claim 19 , wherein each of the delay circuits includes:
a plurality of series-connected delay circuits for generating the delayed internal pulse signal at the respective output terminals; and
a selection circuit, connected to the delay circuits, for receiving the delayed internal pulse signals from the delay circuits and selecting one of the delayed internal pulse signals in accordance with the voltage detection signal.