JP2007244128A - Overcurrent detecting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an overcurrent detecting circuit for reducing occurrences of malfunctions and a power consumption. <P>SOLUTION: The overcurrent detecting circuit for detecting an overcurrent of a main transistor in a switching regulator is provided with a selector for outputting a drain voltage or a source voltage of the main transistor in response to turnon and turnoff of the main transistor, a reference voltage circuit for outputting a voltage as a product of an ON resistor of a comparison transistor applied with a gate voltage at a gate and a current from a constant current source when the main transistor is turned on, and a comparison circuit for comparing outputs from the selector and the reference voltage circuit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an overcurrent detection circuit that can accurately detect overcurrent.

When the drain voltage generated by the on-resistance and current of the main transistor is compared with a certain constant voltage for overcurrent detection in the switching regulator, a detection error occurs due to a variation due to temperature characteristics of the on-resistance of the main transistor.
Therefore, a reference voltage is generated using a reference transistor having the same temperature characteristic as that of the main transistor and a constant current, and the comparison is performed so that the temperature characteristic variation of the main transistor can be offset. .

In a circuit that detects an overcurrent of the main transistor in the switching regulator, the current is detected by converting the current into a voltage using the on-resistance of the main transistor. As this voltage, there is a method of directly detecting a voltage divided by a voltage dividing resistor connected in parallel to the main transistor or a drain voltage of the main transistor (see, for example, Patent Document 1).
JP 2005-333691 A

  However, since the on-resistance of the main transistor is small in the above-described conventional technology, the detection voltage is further reduced when the on-resistance is divided. Further, since the drain voltage when the main transistor is turned on / off becomes a large amplitude voltage, it is not preferable to input the voltage directly to the comparison circuit because malfunctions occur in the comparison circuit or power consumption increases.

  Further, if the first switch transistor and the second switch transistor of the selector are turned on at the same time, a through current flows and the circuit efficiency deteriorates.

  A constant current source is included as a basic circuit of the switching regulator. Nevertheless, it is not preferable to separately configure a constant current source specified only by the overcurrent detection circuit because the circuit scale and current consumption increase.

  A configuration in which a large current is actually passed through the main transistor, an overcurrent detection voltage is generated, and an overcurrent value to be detected is set in a way that ignores testability. In practice, a method is required in which a slight test current is passed through the transistor and the overcurrent value is determined from the drain voltage of the main transistor at that time. However, the drain voltage at that time is very small, and it is difficult to determine the overcurrent value from the voltage.

  Accordingly, an object of the present invention is to provide an overcurrent detection circuit that suppresses the occurrence of malfunction and power consumption.

  In order to solve the above-mentioned problem, an invention according to claim 1 is an overcurrent detection circuit for detecting an overcurrent of a main transistor in a switching regulator, wherein the drain voltage of the main transistor according to on / off of the main transistor Alternatively, a selector that outputs a source voltage, and a reference voltage circuit that outputs a product of a product of an on-resistance of a comparison transistor to which a gate voltage when the main transistor is on is applied to the gate and a current from a constant current source, and And a comparison circuit for comparing the selector output with the reference voltage circuit output.

  The invention according to claim 2 is an overcurrent detection circuit that detects an overcurrent of a main transistor in a switching regulator, and outputs a drain voltage of the main transistor when the main transistor is on, and the main transistor is off A selector for outputting the source voltage of the main transistor, a comparison transistor having the same characteristics as the main transistor, and a gate voltage applied to the gate when the main transistor is on, and a predetermined value for the comparison transistor. A reference voltage circuit that outputs a voltage generated by the predetermined constant current and the on-resistance of the comparison transistor, the selector output, and the reference voltage circuit output. And a comparison circuit for comparison. To.

  The invention according to claim 3 is an overcurrent detection circuit for detecting an overcurrent of a main transistor in a switching regulator, and outputs the drain voltage of the main transistor when the main transistor is on, and the main transistor is off A selector that outputs the source voltage of the main transistor. The selector is turned on when the drain is connected to the drain of the main transistor, the source is connected to the output of the selector, and the main transistor is turned on. And a second switch transistor that is turned off when the main transistor is turned on and is turned off when the main transistor is turned on, and a drain connected to the output of the selector and a source connected to the source of the main transistor. A comparison transistor having the same characteristics as the main transistor, the gate voltage being applied to the gate when the main transistor is on, and a constant current source for supplying a predetermined constant current to the comparison transistor; A reference voltage circuit that outputs a voltage generated by the predetermined constant current and the on-resistance of the comparison transistor, and a comparison circuit that compares the selector output and the reference voltage circuit output. It is characterized by that.

  The invention according to claim 4 is an overcurrent detection circuit for detecting an overcurrent of the main transistor in the switching regulator, and outputs the drain voltage of the main transistor when the main transistor is on, and the main transistor is off A selector that outputs the source voltage of the main transistor. The selector is turned on when the drain is connected to the drain of the main transistor, the source is connected to the output of the selector, and the main transistor is turned on. And a second switch transistor that is turned off when the main transistor is turned on and is turned off when the main transistor is turned on, and a drain connected to the output of the selector and a source connected to the source of the main transistor. A comparison transistor having the same characteristics as the main transistor, the gate voltage being applied to the gate when the main transistor is on, and a constant current source for supplying a predetermined constant current to the comparison transistor; A reference voltage circuit configured to output a voltage generated by the predetermined constant current and an on-resistance of the comparison transistor, and a comparison circuit comparing the selector output and the reference voltage circuit output. The first switch transistor is turned off when the main transistor is turned off, turned on immediately after the second switch transistor is turned off, and the second switch transistor is turned off when the main transistor is turned on. And the first switch transistor is turned on immediately after it is turned off. To.

  The invention described in claim 5 is the invention described in claim 3 or 4, wherein the constant current source is a reference constant current source of the switching regulator.

  According to a sixth aspect of the present invention, in the overcurrent detection circuit according to any one of the first to fourth aspects, the comparison circuit generates a current value corresponding to the selector output voltage. A circuit, a second current conversion circuit that generates a current value according to the reference output voltage, and a current mirror that compares the first current conversion circuit output current and the second current conversion circuit output current And a current comparison circuit.

  According to a seventh aspect of the present invention, in the overcurrent detection circuit according to the sixth aspect, the first current conversion circuit includes a first error amplifier and a first bias transistor that receives an error amplifier output at a gate. And a first resistor that generates a voltage by a current from the first bias transistor, and the first error amplifier makes the selector output voltage and the voltage generated by the first resistor have the same potential. The second current conversion circuit includes a second error amplifier, a second bias transistor that receives an error amplifier output at a gate, and the second current transistor. A second resistor for generating a voltage by a current from the bias transistor, and the second error amplifier is a voltage generated from the reference output voltage and the second resistor. The acts to the same potential, and outputs a current by said second bias transistor, characterized in that the resistance of the first current conversion circuit and said second current conversion circuit variable.

  The invention according to claim 8 is the overcurrent detection circuit according to any one of claims 1 to 4, wherein the reference voltage circuit includes a current mirror circuit that receives a current value of the constant current source, The current mirror circuit has a variable mirror ratio, and outputs a voltage generated by a current generated by the current mirror circuit and an on-resistance of the comparison transistor, and the comparison circuit has a third input having the selector output as a gate input. A third current conversion circuit for generating a current by a source follower by a bias transistor and a third resistor; a fourth bias transistor having a gate input of the reference voltage circuit output; and the same resistance value as the third resistor And a fourth current conversion circuit for generating a current by a source follower by a fourth resistor having characteristics, and the third current conversion circuit Characterized by comprising a current comparator circuit using a current mirror of comparing the output current fourth current converter output current.

  The invention according to claim 9 is the overcurrent detection circuit according to any one of claims 1 to 8, wherein the main transistor has a driver transistor and an on-resistance higher than the on-resistance of the driver transistor. It comprises the parallel connection with the test transistor which has.

  According to the present invention, since the drain voltage only when the main transistor is on is taken out by the selector, the on-resistance of the main transistor can be utilized to the maximum, and a large amplitude voltage does not enter the comparison circuit input. Thus, malfunction of the comparison circuit and increase in current consumption can be avoided. In addition, the reference voltage is generated by the same temperature characteristic-dependent comparison transistor as the main transistor and a constant current source so that the reference voltage has the same temperature characteristic as the main transistor, so overcurrent detection is possible at a constant current value. Can be done.

FIG. 1 is a block diagram showing an embodiment in which an overcurrent detection circuit according to the present invention is applied to a step-up switching regulator.
The reference voltage circuit includes a constant current source 101 used in common with the control circuit unit 119, and a comparison transistor 102 to which a gate voltage when the main transistor (MOS transistor) 116 is turned on, that is, a power supply voltage is applied to the gate. Consists of.
The comparison transistor 102 is made by the same process as the main transistor 116. Therefore, the reference voltage 103 varies with temperature.

  The selector unit has a drain connected to the drain of the main transistor 116, a switch transistor 115 having a source connected to the output 113 of the selector unit, a drain connected to the output 113 of the selector unit, and a source connected to the source of the main transistor 116. The switch transistor 114 is connected.

The main transistor 116 is controlled by the control circuit unit output 118. The input of the selector unit is also controlled by the control circuit unit output 118. Since the switch transistor 114 is turned off and the switch transistor 115 is turned on when the main transistor 116 is on, the selector output 113 outputs the drain voltage of the main transistor 116.
In contrast, when the main transistor 116 is off, the switch transistor 114 is turned on and the switch transistor 115 is turned off, so that the selector output 113 outputs the source voltage (ground voltage) of the main transistor 116.

  The comparison circuit includes error amplifiers 104 and 111, P-type transistors 107 and 110 that receive outputs from the error amplifiers 104 and 111, variable resistors 106 and 109, and a current mirror circuit.

The variable resistors 106 and 109 are made by the same process and have the same temperature characteristics.
In the error amplifier 104, the reference voltage 103 is input to the inverting input, and the feedback voltage 105 is input to the non-inverting input (hereinafter referred to as a normal input), so that the feedback voltage 105 and the reference voltage 103 are equal. The gate voltage of the P-type MOS transistor 107 is adjusted.

  In addition, since the selector output 113 is input to the inverting input and the feedback voltage 112 is input to the normal rotation input, the error amplifier 111 has the gate of the P-type MOS transistor 110 so that the feedback voltage 112 and the selector output 113 are equal. Adjust the voltage.

  The current mirror circuit compares the current I1 flowing through the variable resistor 106 with the current I2 flowing through the variable resistor 109. When the current I1 flowing through the variable resistor 106 is larger than the current I2 flowing through the variable resistor 109, the voltage 108 is “HI”. When the current I1 flowing through the variable resistor 106 is smaller than the current I2 flowing through the variable resistor 109, the voltage 108 becomes a voltage at the “LOW” logic level.

Next, the relationship between each voltage and current when the main transistor 116 is on is shown.
The on-resistance of the comparison transistor 102 is Rref, the on-resistance of the main transistor 116 is Rsense, the constant current value of the constant current source 101 is Iref, the current value that flows when the main transistor 116 is on is Ilx, and the variable resistor 106 The resistance value is R1, and the resistance value of the variable resistor 109 is R2.

Further, since the comparison transistor 102 and the main transistor 116 are manufactured by the same process, they have the same temperature coefficient Tct.
Since the variable resistor 106 and the variable resistor 109 are made by the same process, they have the same temperature coefficient Tcr.
The reference voltage circuit output 103 is set to Vref, and the drain voltage 120 when the main transistor 116 is on is set to Vsense.
The reference voltage circuit output voltage 103 (Vref) and the drain voltage 120 (Vsense) when the main transistor 116 is turned on are expressed by equations (1) and (2).
Vref = Rref * Tct * Iref (1)
Vsense = Rsense * Tct * Ilx (2)

Since the error amplifier 104 acts to make the feedback voltage 105 equal to the reference voltage circuit output 103, the current I1 flowing through the variable resistor 106 is expressed by Equation (3).
I1 = Vref / R1 / Tcr (3)

Similarly, the error amplifier 111 acts to make the feedback voltage 112 equal to the drain voltage 120 when the main transistor 116 is turned on, so that the current I2 flowing through the variable resistor 109 is expressed by Equation (4).
I2 = Vsense / R2 / Tcr (4)

  Due to the configuration of the current mirror circuit, the comparison circuit output 108 becomes a “LOW” logic level voltage when I1 <I2, and becomes a “HI” logic level voltage when I1> I2. That is, at the time of overcurrent, the comparison circuit output voltage 108 becomes a voltage of “LOW” logic level.

As described above, the current at which the comparison circuit output 108 is inverted, that is, the detected overcurrent value I1x is expressed by Expression (5).
Ilx = (Rref * Tct * Iref * R2 * Tcr) / (Rsense * Tct * R1 * Tcr) (5)

Since the temperature coefficient Tct of the above equation (5) is canceled, the equation (6) is obtained.
Ilx = (Rref * Iref * R2) / (Rsense * R1) (6)

  Therefore, overcurrent detection independent of temperature becomes possible. Also, by making R1 and R2 variable, the setting of the detected overcurrent value can be easily changed.

When the main transistor 116 is off, I2 = 0, so that the comparison circuit output voltage 108 is always at the “HI” logic level.
In addition, the overcurrent detection voltage is determined by flowing a small test current to the main driver (main transistor 116) by increasing the mirror ratio of the current mirror circuit of I1 or decreasing the current mirror ratio of I2 during the test. I can do it.

FIG. 2 is a block diagram showing an embodiment in which the overcurrent detection circuit according to the present invention is applied to a step-up switching regulator.
The main transistor 218 includes a driver transistor 213 and a test transistor 212 having a higher on-resistance than the driver transistor 213.
The voltage 216 is a driving voltage for the main transistor 218. The voltage 215 is a test disable voltage. When the voltage 215 is a voltage of “HI” logic level, the driver transistor 213 and the test transistor 212 are switched by the voltage 216.
When the voltage 215 is a “LOW” logic level voltage, the driver transistor is turned off and only the test transistor is driven.

  The selector unit has a drain connected to the drain of the main transistor 218, a switch transistor 210 having a source connected to the output 209 of the selector, a drain connected to the output 209 of the selector, and a source connected to the source of the main transistor 218. Switch transistor 211.

The selector input is a voltage 216. When the voltage 216 becomes a voltage of “HI” logic level, the switch transistor 211 is turned off, and when the switch transistor 211 is turned off, the switch transistor 210 is turned on.
On the other hand, the logic circuit is assembled so that the switch transistor 210 is turned off when the voltage 216 becomes a voltage of “LOW” logic level, and the switch transistor 211 is turned on when the switch transistor 210 is turned off.

  The reference voltage circuit includes a constant current source 201 used in common with the control circuit unit 217, a current mirror 202 that folds back the current value of the constant current source 201, and a gate voltage when the main transistor 218 is turned on at the gate, that is, It is composed of a comparison transistor 203 to which a power supply voltage is applied.

The current mirror can change the mirror ratio by trimming a fuse or a jumper line.
The comparison transistor 203 is made by the same process as the driver transistor 213 and the test transistor 212. Therefore, the reference voltage 204 varies with temperature.

  For example, the comparison circuit unit is made by the same process as the resistor 205, the current value I3 by the source follower circuit of the bias transistor 206, and the resistor 205, and has the same resistance value. The size of the resistor 208 and the bias transistor 206 is also a process. The current value I4 by the source follower circuit composed of the bias transistor 219 is also compared.

  When the current I3 flowing through the resistor 205 is larger than the current I4 flowing through the resistor 208, the voltage 207 becomes a voltage of “HI” logic level, and when the current I3 flowing through the resistor 205 is smaller than the current I4 flowing through the resistor 208, the voltage 207 becomes “ LOW ”logic level voltage.

Next, the relationship between each voltage and current when the main transistor 218 is on is shown.
When the test disable voltage 215 is a “HI” logic level voltage, that is, the on-resistance of the main transistor 218 during normal operation is Rsense, the on-resistance of the comparison transistor 203 is Rref, and the constant current value of the constant current source 201 is Is Iref, the current value that flows when the main transistor 218 is on is Ilx, and the resistance value of the resistor 205 and the resistance value of the resistor 219 are R3.

Since the comparison transistor 204 and the main transistor 218 are made by the same process, they have the same temperature coefficient Tct.
Since the resistor 205 and the resistor 208 are made by the same process, they have the same temperature coefficient Tcr.
The bias transistor 206 and the bias transistor 219 have the same threshold voltage Vth. The reference voltage circuit output 202 is set to Vref, and the drain voltage when the main transistor 218 is turned on, that is, the selector output 209 is set to Vsense.
Let the power supply voltage be Vbat. Further, m is the number of parallel transistors on the constant current source side of the current mirror 202, n is the number of parallel transistors on the folded side, and Imr is the folded current value.

The current value Iref of the constant current source 201 is converted by the current mirror 202 into the following formula (7).
Imr = Iref * n / m (7)

The reference voltage circuit output 204 (Vref) and the drain voltage 209 (Vsense) when the main transistor 218 is turned on are expressed by equations (8) and (9).
Vref = Rref * Tct * Imr (8)
Vsense = Rsense * Tct * Ilx (9)
Since the bias transistor 206 is a source follower with the resistor 205, the flowing current I3 is expressed by Expression (10).
I3 = (Vbat− (Vref + Vth)) / (R3 * Tcr) (10)

Since the bias transistor 219 is a source follower with the resistor 208, the flowing current I4 is expressed by Expression (11).
I4 = (Vbat− (Vsense + Vth)) / (R3 * Tcr) (11)

As described above, the current at which the comparison circuit output 207 is inverted, that is, the detected overcurrent value I1x is expressed by Expression (12).
Ilx = (Rref * Iref * n) / (Rsense * m) (12)

  Therefore, overcurrent detection independent of temperature becomes possible. Further, the detected overcurrent value can be changed by changing n and m.

  If the channel width of the driver transistor 213 is L times the channel width of the test transistor 212, the on-resistance of the test transistor 212 is L times the on-resistance of the driver transistor 213. If L is sufficiently large, since the driver transistor 213 is always off when the test disable voltage 215 is a voltage of “LOW” logic level, the on-resistance of the main transistor 218 is “HI” when the test disable voltage 215 is “HI”. L times the voltage of the logic level. Therefore, at the time of testing, Ilx detects overcurrent at 1 / L times the normal overcurrent detection.

  FIG. 3 is a block diagram showing an embodiment when the overcurrent detection circuit according to the present invention is applied to a step-down switching regulator.

  Since the overcurrent detection circuit shown in the figure is a step-down switching regulator, the main transistor 301 is a P-type MOS transistor. Therefore, the comparison transistor 302 is also a P-type MOS transistor. Is the same as the description of FIG.

FIG. 4 is a block diagram showing a modification of the selector used in the overcurrent detection circuit according to the present invention.
The selector input signal 400 is filtered by a resistor 401 and a capacitor 402. Therefore, when the selector input signal 400 is inverted, the selector operates after a delay by the filter.
The selector input signal 400 is the gate voltage of the main transistor 405, but the drain voltage 406 of the main transistor 405 is not immediately turned on immediately after the gate voltage reaches the “LOW” logic level. Is low. At this time, when the selector operates and the selector outputs a low voltage 407, the comparison circuit outputs an overcurrent detection signal.
Therefore, the drain voltage 406 when the main transistor 405 is completely turned on is output by operating after the delay by the filter.

Further, when the gate voltage becomes a voltage of “HI” logic level, the main transistor 405 is turned off and the drain voltage 406 is lowered.
The selector input signal 400 outputs the source voltage of the main transistor 405, that is, the power supply voltage after outputting the low drain voltage 406 when the main transistor 405 is turned off in order to operate the selector after the delay.
As a result, the comparison circuit outputs an overcurrent detection signal. However, even if overcurrent detection is performed, there is no problem because the main transistor 405 is already turned off. In the figure, reference numerals 403 and 404 denote switch transistors, which correspond to the switch transistors 210 and 211 in FIG. 2, respectively.

FIG. 5 is a block diagram showing another modification of the selector used in the overcurrent detection circuit according to the present invention.
In the selector shown in FIG. 5, the voltage 504 and the drain voltage 501 of the main transistor 500 are input to the selector. The gate voltage of the main transistor 500 is input from the voltage 504 through the delay circuit 506.
When the voltage 504 becomes a voltage of “HI” logic level, the gate voltage of the switch transistor 503 becomes a voltage of “HI” logic level, and the switch transistor 503 is closed.
When the voltage 504 becomes the voltage of the “HI” logic level and the main transistor 500 is turned off after the delay by the delay circuit 506, the drain voltage 501 becomes the voltage of the “LOW” logic level.

When the drain voltage 501 becomes a voltage of “LOW” logic level and the switch transistor 503 is closed, the gate voltage of the switch transistor 502 becomes a voltage of “LOW” logic level, the switch transistor 502 is turned on, and the selector switches the power supply voltage. Output.
When the voltage 504 becomes a “LOW” logic level voltage, the main transistor 500 is turned on after the delay by the delay circuit 506, and the drain voltage 501 becomes a “HI” logic level voltage. The gate voltage of the switch transistor 502 becomes a voltage of “HI” logic level, and the switch transistor 502 is closed. Since the voltage 504 is already at the “LOW” logic level, the switch transistor 503 opens immediately after the switch transistor 502 is closed.

  In FIG. 4, it is necessary to adjust the time constants of the resistor 401 and the capacitor 402 so that the selector outputs the drain voltage 406 after the drain voltage 406 of the main transistor 405 becomes a voltage of “HI” logic level. In addition, since a delay is added, a voltage when the drain voltage 406 is a “LOW” logic level voltage is output, and the comparison circuit always operates.

On the other hand, in FIG. 5, since the selector outputs the drain voltage 501 by detecting that the drain voltage 501 has become the voltage of the “HI” logic level, the time constants of the resistor 401 and the capacitor 402 are adjusted as shown in FIG. I do not need.
The switch transistor 503 of the selector is turned off when the voltage 504 becomes a voltage of “HI” logic level. Since the main transistor 500 is turned off with a delay after the voltage 504 reaches the “HI” logic level voltage, the selector switch transistor 503 is turned off earlier than the drain voltage 501 becomes the “LOW” logic level voltage. . Therefore, the comparison circuit does not malfunction.

[Function and effect]
(Claims 1 to 3)
4. The selector according to claim 1, wherein the drain voltage only when the main transistor is on is taken out by the selector, so that the on-resistance of the main transistor can be utilized to the maximum and a large amplitude voltage does not enter the comparison circuit input. Therefore, malfunction of the comparison circuit and increase in current consumption can be avoided.

  In addition, the reference voltage is generated by the same temperature characteristic-dependent comparison transistor as the main transistor and a constant current source so that the reference voltage has the same temperature characteristic as the main transistor, so overcurrent detection is possible at a constant current value. Can be done.

(Claim 4)
By controlling the on-timing of the switch transistor, it is possible to prevent the first switch transistor and the second switch transistor of the selector from being turned on at the same time and causing a through current to flow.

(Claim 5)
By using the constant current source included as the basic circuit of the switching regulator, the circuit scale and current consumption can be saved.

(Claim 6)
By using a current comparison circuit that converts voltage to current and uses a current mirror, without changing the constant current value of the reference voltage circuit by adjusting the ratio and current mirror ratio when converting voltage to current, It can be compared with the drain voltage of the main transistor.
Further, by changing the current mirror ratio and the ratio for converting the voltage to the current, the overcurrent value can be determined with a small error even with a small test current.

(Claim 7)
According to the sixth aspect of the present invention, it is necessary that the voltage can be converted with a ratio when converting from voltage to current.
Therefore, by adopting the configuration as in claim 7, the voltage-to-current conversion ratio can be changed by the resistance value.

(Claim 8)
By using a source follower without using an error amplifier, the circuit scale and current consumption can be reduced. Further, the overcurrent detection voltage can be changed by changing the mirror ratio by the constant current source.

(Claim 9)
Since a transistor having a large on-resistance and a small transistor are connected in parallel and a transistor having a small on-resistance is used for testing, a test can be performed by applying a small current to the main transistor. Furthermore, waste of space can be saved by operating a transistor with a large on-resistance and a small transistor at the same time in parallel.

  The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. is there. For example, in the above description, the case where a MOS transistor is used has been described. However, the present invention is not limited to this and can be applied to a bipolar transistor.

  The present invention can be used for a semiconductor circuit such as a series regulator that requires overcurrent protection in a driver transistor.

It is a block diagram which shows one Embodiment at the time of applying the overcurrent detection circuit based on this invention to a step-up type switching regulator. 1 is a block diagram showing an embodiment in which an overcurrent detection circuit according to the present invention is applied to a step-up switching regulator. It is a block diagram which shows one Embodiment at the time of applying the overcurrent detection circuit based on this invention to a pressure | voltage fall type switching regulator. It is a block diagram which shows the modification of the selector used for the overcurrent detection circuit which concerns on this invention. It is a block diagram which shows the other modification of the selector used for the overcurrent detection circuit which concerns on this invention.

Explanation of symbols

101 constant current source 102 comparison transistor 103 reference voltage 104, 111 error amplifier 105, 112 feedback voltage 106, 109 variable resistance 107, 110 P-type transistor 108 voltage 113 output 114, 115 switch transistor 116 main transistor

Claims (9)

An overcurrent detection circuit for detecting an overcurrent of a main transistor in a switching regulator,
A selector that outputs a drain voltage or a source voltage of the main transistor in accordance with on / off of the main transistor;
A reference voltage circuit that outputs a product voltage of an on-resistance of a comparison transistor to which a gate voltage when the main transistor is on is applied to a gate and a current from a constant current source;
A comparison circuit for comparing the selector output and the reference voltage circuit output;
An overcurrent detection circuit comprising: An overcurrent detection circuit for detecting an overcurrent of a main transistor in a switching regulator,
A selector that outputs a drain voltage of the main transistor when the main transistor is on, and a source voltage of the main transistor when the main transistor is off;
The comparison transistor has the same characteristics as the main transistor, and includes a comparison transistor in which a gate voltage is applied to the gate when the main transistor is on, and a constant current source that supplies a predetermined constant current to the comparison transistor. A reference voltage circuit that outputs a voltage generated by a predetermined constant current and the on-resistance of the comparison transistor;
A comparison circuit for comparing the selector output and the reference voltage circuit output;
An overcurrent detection circuit comprising: An overcurrent detection circuit for detecting an overcurrent of a main transistor in a switching regulator,
A selector that outputs the drain voltage of the main transistor when the main transistor is on, and that outputs the source voltage of the main transistor when the main transistor is off;
The selector has a drain connected to the drain of the main transistor and a source connected to the output of the selector. The selector is turned on when the main transistor is turned on and turned off when the main transistor is turned off. The drain is connected and the source is connected to the source of the main transistor, and the main transistor is turned off when the main transistor is turned on, and the second switch transistor is turned on when turned off.
The comparison transistor has the same characteristics as the main transistor, and includes a comparison transistor in which a gate voltage is applied to the gate when the main transistor is on, and a constant current source that supplies a predetermined constant current to the comparison transistor. A reference voltage circuit that outputs a voltage generated by a predetermined constant current and the on-resistance of the comparison transistor;
A comparison circuit for comparing the selector output and the reference voltage circuit output;
An overcurrent detection circuit comprising: An overcurrent detection circuit for detecting an overcurrent of a main transistor in a switching regulator,
A selector that outputs the drain voltage of the main transistor when the main transistor is on, and that outputs the source voltage of the main transistor when the main transistor is off;
The selector has a drain connected to the drain of the main transistor and a source connected to the output of the selector. The selector is turned on when the main transistor is turned on and turned off when the main transistor is turned off. The drain is connected and the source is connected to the source of the main transistor, and the main transistor is turned off when the main transistor is turned on, and the second switch transistor is turned on when turned off.
The comparison transistor has the same characteristics as the main transistor, and includes a comparison transistor in which a gate voltage is applied to the gate when the main transistor is on, and a constant current source that supplies a predetermined constant current to the comparison transistor. A reference voltage circuit that outputs a voltage generated by a predetermined constant current and the on-resistance of the comparison transistor;
A comparison circuit for comparing the selector output and the reference voltage circuit output;
With
The first switch transistor is turned off when the main transistor is turned off, and turned on immediately after the second switch transistor is turned off.
The overcurrent detection circuit, wherein the second switch transistor is turned off when the main transistor is turned on, and is turned on immediately after the first switch transistor is turned off. The overcurrent detection circuit according to claim 3 or 4,
The overcurrent detection circuit, wherein the constant current source is a reference constant current source of the switching regulator. In the overcurrent detection circuit according to any one of claims 1 to 4,
The comparison circuit is
A first current conversion circuit for generating a current value according to the selector output voltage;
A second current conversion circuit for generating a current value according to the reference output voltage;
A current comparison circuit using a current mirror for comparing the first current conversion circuit output current and the second current conversion circuit output current;
An overcurrent detection circuit comprising: The overcurrent detection circuit according to claim 6,
The first current conversion circuit includes:
A first error amplifier; a first bias transistor that receives an error amplifier output at a gate; and a first resistor that generates a voltage by a current from the first bias transistor. The selector output voltage and the voltage generated from the first resistor act to have the same potential, and output the current by the first bias transistor,
The second current conversion circuit includes:
A second error amplifier; a second bias transistor that receives an error amplifier output at a gate; and a second resistor that generates a voltage by a current generated by the second bias transistor. The reference output voltage and the voltage generated from the second resistor act to have the same potential, and output the current by the second bias transistor,
An overcurrent detection circuit, wherein resistances of the first current conversion circuit and the second current conversion circuit are variable. In the overcurrent detection circuit according to any one of claims 1 to 4,
The reference voltage circuit has a current mirror circuit that receives a current value of the constant current source, the current mirror circuit has a variable mirror ratio, and is generated by a current from the current mirror circuit and an on-resistance of the comparison transistor. Output the voltage to
The comparison circuit includes a third current conversion circuit that generates a current by a source follower including a third bias transistor having the selector output as a gate input and a third resistor,
A fourth current conversion circuit for generating a current by a source follower including a fourth bias transistor having the reference voltage circuit output as a gate input and a fourth resistor having the same resistance value and characteristics as the third resistor;
An overcurrent detection circuit comprising: a current comparison circuit using a current mirror for comparing the third current conversion circuit output current and the fourth current conversion circuit output current. The overcurrent detection circuit according to any one of claims 1 to 8,
An overcurrent detection circuit, wherein the main transistor comprises a parallel connection of a driver transistor and a test transistor having an on-resistance higher than the on-resistance of the driver transistor.

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