MULTI-FUNCTION TERMINAL OF POWER SUPPLY CONTROLLER FOR FEEDBACK SIGNAL INPUT AND OVER-TEMPERATURE PROTECTION

1. Field of Invention

The present invention relates to a power converter, and more particularly, the present invention relates to a control circuit having a multi-function terminal of power converter.

2. Description of Related Art

FIG. 1 shows prior art of a power converter. The power converter comprises a boost converter 30, a controller (CNTR) 50, a thermal device 40 and a voltage divider developed by resistors 41 and 42. The boost converter 30 includes an inductor 10, a transistor 15, a rectifier 20 and a capacitor 25. One terminal of the inductor 10 receives an input voltage V_IN. The other terminal of the inductor 10 is connected to an anode of the rectifier 20 and a drain of the transistor 15. A source of the transistor 15 is connected to a ground. A gate of transistor 15 is coupled to a switching terminal SW (not shown) of the controller 50 and controlled by a switching signal S_W. A cathode of the rectifier 20 is connected to one terminal of the capacitor 25. The other terminal of the capacitor 25 is connected to the ground. An output voltage V_Ois generated across the capacitor 25 and is the same as an output of the boost converter 30. The output of the boost converter 30 is also an output of the power converter.

The controller 50 generates the switching signal S_Wto switch the transistor 15 for producing the output voltage V_Oof the power converter. A feedback signal V_FBis generated at a joint of the resistors 41 and 42 of the voltage divider in response to the output voltage V_O. The feedback signal V_FBis applied to a feedback terminal FB (not shown) of the controller 50 for generating the switching signal S_Wand regulating the output voltage V_O. An over-temperature signal S_OTis generated from the thermal device 40 coupled to the controller 50 for over-temperature protection. That is to say, the controller 50 performs over-temperature protection in accordance with the over-temperature signal S_OTgenerated by the thermal device 40.

An object of the present invention is to provide a multi-function terminal for a switching power supply controller. This terminal is utilized to receive a feedback signal and connect to a thermal device for over-temperature protection.

To achieve the aforementioned object, the present invention provides a control circuit having the multi-function terminal, comprising: a switching circuit, the switching circuit generating a switching signal in response to a feedback signal; a sample-and-hold circuit, the sample-and-hold circuit coupled to the multi-function terminal for generating a sample voltage by sampling the feedback signal during a first period; a detection circuit, the detection circuit coupled to the multi-function terminal during a second period for generating a detection voltage; and a comparator, the comparator comparing the detection voltage and the sample voltage for generating an over-temperature signal, wherein the over-temperature is couple to disable the switching signal.

The aforementioned first period is disabled when the second period is enabled.

To achieve the aforementioned object, the present invention further provides a control circuit having a multi-function terminal, comprising: a switching circuit, generating a switching signal; a plurality of function circuits, coupled to the multi-function terminal and generating a plurality of function signals based on a signal on the multi-function terminal; and a comparator, comparing the function signals for generating an output signal to disable the switching circuit generating the switching signal.

The rest of the aforementioned function circuits are disabled when one of the aforementioned function circuits is enabled.

FIG. 2 shows a schematic diagram of a preferred embodiment of a power converter in accordance with the present invention. The power converter comprises a boost converter 30, a control circuit (CNTR) 100, a thermal device R_Tand a voltage divider formed by resistors 41 and 42. Comparing with the FIG. 1, the control circuit 100 is provided with a multi-function terminal M in this preferred embodiment. The power converter further comprises a resistor 45 coupled to the thermal device R_Tin parallel in accordance with the present invention. The resistor 45 is coupled between the multi-function terminal M of the control circuit 100 and a joint of the resistors 41 and 42. The multi-function terminal M is utilized to receive a feedback signal V_FBand connect to the thermal device R_Tfor over-temperature protection. The feedback signal V_FBis correlated to an output voltage V_Oof the power converter. The resistor 45 is connected to the thermal device R_Tin parallel for adjusting the over-temperature protection. The thermal device R_Thas a negative temperature coefficient. In other words, the resistance of the thermal device R_Tis increased once the temperature decreases. The resistance of the thermal device R_Tis decreased once the temperature increases.

FIG. 3 is a preferred embodiment of the control circuit 100 in accordance with the present invention. The control circuit 100 comprises a comparator 160, a switching circuit, and a plurality of function circuits comprising a sample-and-hold circuit and a detection circuit. The sample-and-hold circuit is developed by a switch 102 and a capacitor 103. The feedback signal V_FBis applied to the multi-function terminal M of the control circuit 100. One terminal of the switch 102 is coupled to the multi-function terminal M for receiving the feedback signal V_FB. The other terminal of the switch 102 is coupled to one terminal of the capacitor 103. The other terminal of the capacitor 103 is coupled to the ground. The switch 102 is used for sampling the feedback signal V_FBand a control terminal of the switch 102 is controlled by a first timing signal S₁. The capacitor 103 is used for holding the feedback signal V_FB. A sample voltage (first function signal) V_SPis generated across the capacitor 103 in response to the feedback signal V_FBduring a first period. The first period is generated by an on-time period of the first timing signal S₁. The sample voltage V_SPis correlated to the feedback signal V_FB. The feedback signal V_FBis correlated to the output voltage V_Oof the power converter.

The switching circuit is formed by an error amplifier 110, a capacitor 115, an oscillation circuit (OSC) 130, a comparator 120, an inverter 140, a flip-flop 145 and an AND gate 150. The oscillation circuit 130 generates a pulse signal PLS, a ramp signal RMP, the first timing signal S₁, a second timing signal S₂and a third timing signal S₃. The sample voltage V_SPgenerated across the capacitor 103 is coupled to a negative input of the error amplifier 110 when the switch 102 controlled by the first timing-signal S₁is turned on. A positive input of the error amplifier 110 has a reference signal V_Rfor the output regulation. An output of the error amplifier 110 is coupled to one terminal of the capacitor 115 for the frequency compensation. The Other terminal of the capacitor 115 is coupled to the ground. The output of the error amplifier 110 is further coupled to a positive input of the comparator 120.

The ramp signal RMP is supplied to a negative input of the comparator 120. Comparing the ramp signal RMP with a signal at the output of the error amplifier 110, a reset signal is generated at an output of the comparator 120 to reset the flip-flop 145. A reset input R of the flip-flop 145 receives the reset signal once the ramp signal RMP is larger than the signal at the output of the error amplifier 110. An input of the inverter 140 receives the pulse signal PLS. An output of the inverter 140 is coupled to a clock input CK of the flip-flop 145. That is to say, the oscillation circuit 130 generates the pulse signal PLS to turn on the flip-flop 145 via the inverter 140. The output of the inverter 140 and an output of the flip-flop 145 are connected to the AND gate 150 respectively for generating a switching signal S_Wwith a switching cycle. The pulse signal PLS provides a limitation to a maximum on-time period of the switching signal S_W.

The detection circuit is developed by a switch 105 and a current source 106. One terminal of the switch 105 is coupled to the multi-function terminal M. The other terminal of the switch 105 is coupled to one terminal of the current source 106. The other terminal of the current source 106 is coupled to the ground. In other words, the current source 106 is coupled to the multi-function terminal M via the switch 105. A detection voltage (second function signal) V_Mwill be generated at the multi-function terminal M when the switch 105 controlled by the second timing-signal S₂is turned on and a current I₁₀₆determined by the current source 106 is flowed into the multi-function terminal M. That is to say, the current source 106 is associated with the thermal device R_Tto generate the detection voltage V_M. The detection voltage V_Mis generated during a second period generated by an on-time period of the second timing signal S₂.

The one terminal of the capacitor 103 is further coupled to a positive input of the comparator 160. The sample voltage V_SPgenerated across the capacitor 103 is applied to the positive input of the comparator 160 during the first period generated by an on-time period of the first timing signal S₁. A negative input of the comparator 160 is coupled to the multi-function terminal M through an over-temperature threshold 165. An over-temperature signal S_OTgenerated at an output of the comparator 160. The over-temperature signal S_OTwill be latched into the flip-flop 145. The comparator 160 compares the detection voltage V_M. with the sample voltage V_SPfor generating the over-temperature signal S_OT. The over-temperature signal S_OTis used to disable the switching signal S_W. In addition, the control circuit 100 further comprises the over-temperature threshold 165 for generating the over-temperature signal S_OT.

The oscillation circuit 130 generates the timing signals S₁, S₂and S₃once the switching signal S_Wis disabled. When the first timing signal S₁is enabled and the second timing signal S₂is disabled, the feedback signal V_alis sampled into the capacitor 103. In the meantime, the switch 102 is turned on and the switch 105 is turned off. The sample-and-hold circuit developed by the switch 102 and the capacitor 103 generates the sample voltage V_SPby sampling the feedback signal V_FBduring the first period. When the second timing signal S₂is enabled, the first timing-signal S₁is disabled, the current I₁₀₆determined by the current source 106 is flowed into the multi-function terminal M. The detection voltage V_Mwill be applied to the negative input of the comparator 160 via the over-temperature threshold 165. In the meantime, the switch 102 is turned off and the switch 105 is turned on. Therefore, the comparator 160 is utilized to generate the over-temperature signal S_OTby comparing the detection voltage V_Mwith the sample voltage V_SP. The over-temperature signal S_OTis enabled once the value of the sample voltage V_SPis lower than the value of the detection voltage V_M.

The feedback signal V_FBis divided by the output voltage V_Othrough the voltage divider. The feedback signal V_FBcan be written by the following,

VFB=R42R41+R42×Vo(1)

The equivalent resistance R_Dis determined by the resistors 41 and 42.

RD=R41×R42R41+R42(2)

The equivalent resistance R_PTis determined by the resistor 45 and the thermal device R_T.

RPT=RT×R45RT+R45(3)

The equivalent resistance R_EQis generated by the equivalent resistance R_Dplus the equivalent resistance R_PTas below,

R_EQ=R_D+R_PT  (4)

The equivalent voltage V_DPis generated by the current I₁₀₆and the equivalent resistance R_EQas below,

V_DP=I₁₀₆×R_EQ  (5)

The detection voltage V_Mis generated by the feedback signal V_FBminus the equivalent voltage V_DPas below,

V_M=V_FB−V_DP  (6)

The detection voltage V_Mwill be generated at the multi-function terminal when the current I₁₀₆is flowed into the multi-function terminal M.

The control circuit 100 further comprises a flip-flop 170. An input D of the flip-flop 170 is coupled to the output of the comparator 160 for receiving the over-temperature signal S_OT. A clock input CK of the flip-flop 170 receives the third timing signal S₃to trigger the flip-flop 170. A reset input R of the flip-flop 170 is rested by a signal RST. An output Q of the flip-flop 170 is connected to an input D of the flip-flop 145 for controlling the switching signal S_Win accordance with the over-temperature signal S_OT

When the temperature on the power converter is at a low level, the resistance of the thermal device R_Tis increased because the thermal device R_Thas a negative temperature coefficient as mentioned previously. The equivalent resistances R_PTand R_EQare increased accordingly. The equivalent voltage V_DPis thus increased and the detection voltage V_Mwill be decreased. Since the equivalent voltage V_DPis higher than the over-temperature threshold 165, the over-temperature signal S_OTgenerated by the output of the comparator 160 will be logic-high level. The signal S_Tis a logic-high level once the over-temperature signal S_OTis a logic-high level and the third timing signal S₃is enabled. The flip-flop 145 is thus enabled for generating the switching signal S_W.

On the other hand, the resistance of the thermal device R_Tis decreased when the temperature on the power converter is at a high level. The equivalent resistances R_PTand R_EQare decreased accordingly. The equivalent voltage V_DPis thus decreased and the detection voltage V_Mwill be increased. Since the equivalent voltage V_DPis lower than the over-temperature threshold 165, the over-temperature signal S_OTgenerated by the output of the comparator 160 will be a logic-low level. The signal S_Tis a logic-low level once the over-temperature signal S_OTis a logic-low level and the flip-flop 170 is disabled. The flip-flop 145 and the switching signal S_Ware thus disabled for over-temperature protection.

FIG. 4 shows the waveforms of the pulse signal PLS, the ramp signal RMP and the timing signals S₁-S₃in accordance with the present invention. The ramp signal RMP is decreased when the pulse signal PLS is enabled, and the ramp signal RMP is increased once the pulse signal PLS is disabled. During the first period, generated by the on-time period of the first timing signal S₁, the first timing signal S₁is enabled to turn on the switch 102 for sampling the feedback signal V_FBinto the capacitor 103. The sample voltage V_SPis generated across the capacitor 103. Thus, the switching circuit generates the switching signal S_Wfor the output regulation in response to the feedback signal V_FB. In addition, when the first timing signal S₁is enabled, the timing signals S₂and S₃are disabled. During the second period, generated by an on-time period of the second timing signal S₂, the second timing signal S₂is enabled to turn on the switch 105 and then the current source 106 is coupled to the multi-function terminal M for generating the detection voltage V_M. When the second timing signal S₂is enabled and the switch 105 is turned on, the current I₁₀₆determined by the current source 106 flows into the multi-function terminal M. In addition, when the second timing signal S₂is enable, the first timing signal S₁is disable. As mentioned previously, the on-time period of the third timing signal S₃is smaller than the on-time period of the second timing signal S₂. The signal S_Tgenerated by the flip-flop 170 will be a logic-low level when the third timing signal S₃is enabled and the over-temperature signal S_OTgenerated by the output of the comparator 160 is a logic-low level. When the signal S_Tis a logic-low level and the flip-flop 145 is disabled, the switching signal S_Wis thus disabled for over-temperature protection.

Based on the present invention, an additional terminal is not required to be added the control circuit 100. Therefore, the terminals of the control circuit 100 can be reduced and cost for production will also be reduced.