CN101739112B - Low-voltage slow start circuit - Google Patents

Abstract

The invention discloses a low-voltage slow start circuit, comprising a transistor MOS1 and a control loop, the transistor MOS1 is an N-channel MosFET, the drain of the transistor MOS1 is connected to the main input voltage Vin1, and the source of the transistor MOS1 is connected to the output voltage Vout, The gate of the transistor MOS1 is connected to the control loop, and the other end of the control loop is connected to the auxiliary input voltage Vin2. Due to the use of two input voltages Vin1 and Vin2 with a difference and the difference is greater than the threshold voltage of the transistor MOS1, the transistor MOS1 can work normally. It is turned on, and because the control loop controls the conduction time of the transistor MOS1, and the output voltage rises smoothly, so as to realize the functions of low voltage slow start and sequence control, and also solve the problem of hiccups in the output voltage.

Description

A low voltage slow start circuit

technical field

The invention relates to the field of server power supplies, in particular to a low-voltage slow-start circuit.

Background technique

When the ATX (AT eXternal) power supply is used in the server system, multiple single boards are powered on in the system, and the multi-channel output of the single board is required to have the function of power-on slow start, and also to control the sequence of timing and improve hot swap The impact on the inside of the power supply raises the need for a slow start circuit. Generally, slow start circuits are more common in communication systems, and the input and output voltages are mostly 48V, which are mostly implemented by controlling P-channel MosFETs (P-channel field effect transistors). When used at lower voltages such as 3V, due to the The threshold voltage of the tube) is mostly around 3V, and the MosFET will be in a slightly turned-on state. At this time, the MosFET will consume a lot of power and be easily damaged.

Contents of the invention

The problem to be solved by the present invention is to provide a low-voltage slow-start circuit, which solves the problems of easy loss of MosFETs and hiccups in the output voltage when the existing slow-start circuit is applied to low voltage, and the demand for timing control.

In order to solve the above problems, the present invention provides a low-voltage slow start circuit, including a transistor MOS1 and a control loop, the transistor MOS1 is an N-channel MosFET, the drain of the transistor MOS1 is connected to the main input voltage Vin1, and the source of the transistor MOS1 The pole is connected to the output voltage Vout, the gate of the transistor MOS1 is connected to the control loop, and the other end of the control loop is connected to the auxiliary input voltage Vin2, which is used to control the conduction time of the transistor MOS1, and to make the output voltage Vout rise smoothly, and the auxiliary input voltage Vin2 is high is higher than the main input voltage Vin1, and the higher voltage value is greater than the threshold voltage of the transistor MOS1, the control loop includes a sequential circuit and an output control circuit, and the sequential circuit and the output control circuit are connected in series to the auxiliary input voltage Vin2 and the gate of the transistor MOS1 Between, the other end of the output control circuit is connected to the auxiliary input voltage Vin2, the sequential circuit includes resistors R1, R3 and R4, capacitor C2 and comparator U1, the resistors R1 and R4 are connected in series between the auxiliary input voltage Vin2 and the ground wire Between, the junction of resistors R1 and R4 is connected to the negative terminal of comparator U1; the resistor R3 and capacitor C2 are connected in series between the auxiliary input voltage Vin2 and the ground wire, and the junction of resistor R3 and capacitor C2 is connected to the positive terminal of comparator U1 connected, the comparison output terminal of the comparator U1 is connected to the output control circuit, the output control circuit includes resistors R2, R5 and R6 and a capacitor C3, and the resistors R2, R5 and R6 are connected in series between the auxiliary input voltage Vin2 and the ground wire, The junction of resistors R2 and R5 is connected to the sequential circuit, the resistor R2 plays a role of limiting the current, the positive pole of capacitor C3 is connected to the junction of R5 and R6, the negative pole is connected to the other end of R6, the common terminal of resistors R5, R6 and capacitor C3 is connected to The gates of the transistor MOS1 are connected.

Preferably, a fuse F1 is further included, and the fuse F1 is connected in series between the main input voltage Vin1 and the drain of the transistor MOS1.

Preferably, a capacitor C1 is further included, and the capacitor C1 is connected in series between the drain of the transistor MOS1 and the ground.

Preferably, when used in multi-channel timing control, the comparators of each single-channel low-voltage slow-start circuit are connected to the same negative terminal voltage.

Preferably, the capacitor C2 is a capacitor with a capacitance value between 0.01uF-22uF and/or a ceramic capacitor or a tantalum capacitor and/or R1/R3/R4 is 10K.

Preferably, the capacitor C3 is a capacitor and/or a tantalum capacitor with a capacitance value between 10uF˜47uF.

Preferably, the voltage value of the main input voltage Vin1 is between 1V and 10V, the voltage value of the auxiliary input voltage Vin2 is between 4V and 12V, and the voltage of the auxiliary input voltage Vin2 is higher than the main input voltage Vin1 and higher than Out of 3V or more.

Because the low-voltage slow start circuit uses two input voltages whose difference is greater than the threshold voltage of the transistor, and the transistor is an N-channel MosFET, the transistor can be turned on normally, and because of the control loop, the turn-on time of the transistor and The output voltage is controlled, thereby solving the problems that the MOS tube is easily damaged and the output voltage hiccups when the existing slow-start circuit is applied to low voltage, and the need for timing control.

Description of drawings

Fig. 1 is a schematic structural diagram of the first embodiment of the low voltage slow start circuit of the present invention;

Fig. 2 is a schematic structural diagram of the second embodiment of the low voltage slow start circuit of the present invention;

Fig. 3 is a schematic structural diagram of the third embodiment of the low-voltage slow-start circuit of the present invention;

4 is a schematic structural diagram of a fourth embodiment of a low-voltage slow-start circuit of the present invention;

Fig. 5 is a schematic structural diagram of a fifth embodiment of the low-voltage slow-start circuit of the present invention;

Fig. 6 is a schematic diagram of the slow start time of the fifth embodiment of the low voltage slow start circuit of the present invention;

7 is a schematic structural diagram of the sixth embodiment of the low-voltage slow-start circuit of the present invention;

Detailed ways

The low-voltage slow start circuit of the present invention adopts the main input voltage Vin1 and the auxiliary input voltage Vin2 respectively connected to the drain and gate of the transistor, and the voltage value of the auxiliary input voltage higher than the main input voltage is greater than the threshold voltage of the transistor, so that the N-type Transistor MOS1 can be turned on normally, and a control loop is connected in series between the drain of the transistor and the auxiliary input voltage to control the turn-on time of the transistor and realize timing control. The control loop can also control the gate voltage of the transistor to rise smoothly. Thus, the output voltage rises smoothly, which solves the problem of hiccups in the output voltage

The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

Embodiment one:

As shown in Figure 1, the low-voltage slow start circuit includes a transistor MOS1 and a control loop, the transistor MOS1 is an N-channel MosFET, the drain of the transistor MOS1 is connected to the main input voltage Vin1, the source of the transistor MOS1 is connected to the output voltage Vout, and the transistor MOS1 is connected to the output voltage Vout. The gate of MOS1 is connected to the control loop, and the other end of the control loop is connected to the auxiliary input voltage Vin2, which is used to control the conduction time of the transistor MOS1 and make the output voltage rise smoothly. The auxiliary input voltage Vin2 is higher than the main input voltage Vin1, and high The output voltage value is greater than the threshold voltage of transistor MOS1.

Its working process is: when the circuit is powered on, the control voltage output by the control loop cannot turn on the transistor MOS1, and the source of the transistor MOS1 has no output. When the circuit is powered on, the control voltage output by the control loop can turn on the transistor MOS1 , and the output voltage Vout of the source of the transistor MOS1 rises smoothly, and there is a certain interval between the output voltage Vout and the input voltage, so as to realize the function of low-voltage slow start.

Embodiment two:

The difference between this embodiment and the first embodiment above is that a fuse F1 is connected between the drain of the transistor MOS1 and the main input voltage Vin1 in this embodiment. As shown in FIG. 2 , the fuse F1 functions as a circuit protection.

Other technical features in the second embodiment are the same as those in the first embodiment, and will not be repeated here.

Embodiment three:

The main difference between this embodiment and the first embodiment above is that this embodiment connects an energy storage capacitor C1 between the drain of the transistor MOS1 and the ground, as shown in FIG. 3 .

Other technical features in the third embodiment are the same as those in the first embodiment, and will not be repeated here.

Embodiment four:

The difference between this embodiment and the above-mentioned embodiments 1, 2, and 3 is that the control loop in embodiment 1 is further limited in this embodiment, and the control loop is specifically realized by a sequential circuit and an output control circuit. Simultaneously, combining the characteristics of Embodiments 2 and 3, an energy storage capacitor and a fuse are connected to the drain of the transistor, as shown in Figure 4, the low-voltage slow start circuit includes a fuse F1, a capacitor C1, a transistor MOS1 and a control circuit, a fuse F1 and a capacitor C1 is connected in series between the main input voltage Vin1 and the ground, the junction of the fuse F1 and the capacitor C1 is connected to the drain of the transistor MOS1, the control circuit includes a timing circuit and an output control circuit, and the timing circuit and the output control circuit are connected in series to the auxiliary input voltage Vin2 Between and the gate of the transistor MOS1, the other end of the output control circuit is connected with the auxiliary input voltage Vin2.

Its working process is: when the auxiliary input voltage Vin2 is powered on, the sequential circuit outputs a low level to the output control circuit, and the output control circuit outputs a control voltage to the transistor MOS1. At this time, the transistor cannot be turned on, and the output voltage Vout is zero; When the auxiliary input voltage Vin2 is powered on, the sequential circuit outputs a high level to the output control circuit, and the output control circuit outputs another control voltage to the transistor MOS1, when the voltage difference between the gate and drain of the transistor is greater than the threshold of the transistor voltage, and when the main input voltage Vin1 is powered on, the source of the transistor has an output, and the output voltage Vout is greater than zero.

Other technical features in the fourth embodiment are the same as those in the first embodiment, and will not be repeated here.

Embodiment five:

The difference between this embodiment and the above-mentioned fourth embodiment mainly lies in that the sequential circuit and the output control circuit in the fourth embodiment are further limited in this embodiment, and the sequential circuit and the output control circuit are defined by the specific ones in the fifth embodiment components, as shown in Figure 5 is a schematic structural diagram of the third embodiment of the low-voltage slow start circuit of the present invention, its specific structure is:

The sequential circuit includes resistors R1, R3 and R4, capacitor C2 and comparator U1. Resistors R1 and R4 are connected in series between the auxiliary input voltage Vin2 and the ground wire. The junction of resistors R1 and R4 is connected to the negative terminal of comparator U1. Provide a fixed voltage; resistor R3 and capacitor C2 are connected in series between the auxiliary input voltage Vin2 and the ground wire, the junction of resistor R3 and capacitor C2 is connected to the positive terminal of comparator U1, and the comparison output terminal of comparator U1 is connected to the output The control circuit controls the flipping time of the comparator U1 by adjusting C2;

The output control circuit includes resistors R2, R5, R6 and capacitor C3. The resistors R2, R5, and R6 are connected in series between the auxiliary input voltage Vin2 and the ground wire. The junction of the resistors R2 and R5 is connected to the comparison output terminal of the comparator U1. Resistor R2 acts to limit the current, capacitor C3 is connected in parallel to resistor R6, the common terminal of resistors R5, R6 and capacitor C3 is connected to the gate of transistor MOS1, RC3 (R refers to resistors R2 and R5 connected in series and then connected to resistor R6 Parallel equivalent resistance) charging controls the conduction of MOS1.

The specific working process of the circuit shown in Figure 5 is: when the auxiliary input voltage Vin2 is powered on, the voltage is divided by R1 and R4, the negative terminal voltage of comparator U1 is higher than the positive terminal voltage, and the comparison output terminal of comparator U1 outputs Low (low level), when the voltage difference between the gate and drain of the transistor MOS1 does not reach the conduction threshold of the transistor, the source of the transistor MOS1 has no output; when the auxiliary input voltage Vin2 is powered on, the capacitor C2 is charged through R3 , when the voltage charged at the positive terminal is higher than the voltage at the negative terminal, the comparison output terminal of the comparator U1 will turn over and change from Low to High (high level). At this time, the auxiliary input voltage Vin2 charges C3 through R2, R5 and R6. The voltage of C3 rises smoothly. When the voltage difference between the gate and drain of transistor MOS1 is higher than the threshold voltage of transistor MOS1 and the main input voltage Vin1 is powered on, the voltage output terminal Vout will output. Because the capacitor C3 makes the gate of the transistor MOS1 rise smoothly, the source of the transistor also rises smoothly. The overall process is a slow start process.

The slow start time consists of two parts, as shown in Figure 6, one part is the delayed flip time t1 of the comparator, and the other part is the time t2 when the capacitor C3 is charged to the transistor conduction threshold, as shown in Figure 6. in,

t1＝R3*C2*ln[R1/(R1+R4)]

ln represents the logarithmic function with the constant e as the base.

The value of t1 is controlled by adjusting the size of R3/C2/R1/R4. When in use, set R1/R4 as a fixed value first, and adjust R3 or C2 according to the above equation to change the value of t1. Generally, R1/R3/R4 can be fixed at 10K, and the capacitance value of C2 can be adjusted to control the delay time t1 of the comparator. The rise time t2 of the output voltage Vout is adjusted by adjusting the capacitance value of C3. In the timing control, t2 is very short and ignored. Thus, timing control of the output voltage Vout is realized by adjusting the value of the capacitance of C2.

Other technical features in the fifth embodiment are the same as those in the fourth embodiment, and will not be repeated here.

Embodiment six:

When the low-voltage slow-start circuit is used in single-way sequence control, it can be connected according to Embodiment 5. Embodiment 6 is a circuit diagram when the low-voltage slow-start circuit is used in two-way sequence control. The connection method is shown in Figure 7 As shown, that is, the combination of the two circuits shown in Embodiment 5, the main input voltage of the second single-channel low-voltage slow-start circuit is Vin3, and the auxiliary input voltage is connected to the auxiliary input voltage Vin2 of the first single-channel low-voltage slow-start circuit , the negative terminal of the comparator U2 is connected to the negative terminal of the comparator U1, and the capacitors C2 and C4 take different values to complete the power-on sequence sequencing of the output voltages Vout1 and Vout2, and other technical features are the same as those in the fifth embodiment.

The embodiments of the present invention described above are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (7)

1. A low-voltage slow-start circuit, characterized in that it comprises transistor MOS1 and a control loop, said transistor MOS1 is an N-channel MosFET, the drain of transistor MOS1 is connected to the main input voltage Vin1, and the source of transistor MOS1 is connected to the output Voltage Vout, the gate of the transistor MOS1 is connected to the control loop, and the other end of the control loop is connected to the auxiliary input voltage Vin2, which is used to control the conduction time of the transistor MOS1 and make the output voltage Vout rise smoothly. The auxiliary input voltage Vin2 is higher than the main input Voltage Vin1, and the higher voltage value is greater than the threshold voltage of the transistor MOS1, the control loop includes a sequential circuit and an output control circuit, the sequential circuit and the output control circuit are connected in series between the auxiliary input voltage Vin2 and the gate of the transistor MOS1, The other end of the output control circuit is connected to the auxiliary input voltage Vin2. The sequential circuit includes resistors R1, R3 and R4, capacitor C2 and comparator U1. The resistors R1 and R4 are connected in series between the auxiliary input voltage Vin2 and the ground wire. The resistor The junction of R1 and R4 is connected to the negative terminal of comparator U1; the resistor R3 and capacitor C2 are connected in series between the auxiliary input voltage Vin2 and the ground wire, and the junction of resistor R3 and capacitor C2 is connected to the positive terminal of comparator U1. The comparison output terminal of the comparator U1 is connected to an output control circuit, the output control circuit includes resistors R2, R5 and R6 and a capacitor C3, the resistors R2, R5 and R6 are connected in series between the auxiliary input voltage Vin2 and the ground wire, and the resistor R2 and The contact of R5 is connected to the sequential circuit, the resistor R2 plays the role of limiting the current, the positive pole of the capacitor C3 is connected to the contact of R5 and R6, the negative pole is connected to the other end of R6, the common terminal of the resistors R5, R6 and the capacitor C3 is connected to the transistor MOS1 The grids are connected. 2 . The low-voltage slow-start circuit according to claim 1 , further comprising a fuse F1 connected in series between the main input voltage Vin1 and the drain of the transistor MOS1 . 3. The low-voltage slow-start circuit according to claim 1 or 2, further comprising a capacitor C1 connected in series between the drain of the transistor MOS1 and the ground. 4 . The low-voltage slow-start circuit according to claim 1 , wherein when used in multi-channel sequential control, the comparators of each single-channel low-voltage slow-start circuit are connected to the same negative terminal voltage. 5. The low-voltage slow-start circuit according to claim 1, wherein the capacitor C2 is a capacitor with a capacitance value between 0.01uF and 22uF; and / or Capacitor C2 is a ceramic capacitor or a tantalum capacitor; and / or R1/R3/R4 is 10K. 6. The low-voltage slow-start circuit according to claim 1, wherein the capacitor C3 is a capacitor with a capacitance value between 10uF and 47uF; and / or Capacitor C3 is a tantalum capacitor. 7. The low-voltage slow-start circuit according to claim 1 or 2, wherein the voltage value of the main input voltage Vin1 is between 1V and 10V, and the voltage value of the auxiliary input voltage Vin2 is between 4V and 12V Between, the auxiliary input voltage Vin2 is higher than the main input voltage Vin1 by more than 3V.

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