CN209963949U - Soft start circuit of current type pulse width modulator chip - Google Patents
Soft start circuit of current type pulse width modulator chip Download PDFInfo
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- CN209963949U CN209963949U CN201920849717.1U CN201920849717U CN209963949U CN 209963949 U CN209963949 U CN 209963949U CN 201920849717 U CN201920849717 U CN 201920849717U CN 209963949 U CN209963949 U CN 209963949U
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Abstract
The utility model discloses a soft start circuit of current type pulse width modulator chip, including current type pulse width modulator chip and soft start circuit, when current type pulse width modulator chip starts, the compensation output pin of current type pulse width modulator chip is the soft start circuit power supply, soft start circuit passes through energy storage capacitor energy storage, fall at current type pulse width modulator chip power VCC and the power VCC falls to chip shutdown voltage after, soft start circuit's energy storage capacitor passes through current type pulse width modulator chip and refers to output Vref pin for its power supply, make current type pulse width modulator chip still can continue to work for a certain time, when the power VCC falls the certain voltage under to chip shutdown voltage, soft start circuit's energy storage capacitor discharges fast, make preparation for next start. The power supply is started without failure in a frequent startup and shutdown state, and meanwhile, the capacitance value of the energy storage capacitor, namely the starting capacitor, can be remarkably reduced.
Description
Technical Field
The utility model belongs to the technical field of switching power supply, concretely relates to soft start circuit of current type pulse width modulator chip.
Background
Current-mode pulse width modulator chips (UC3842, 3843, 3844, etc.) are commonly used in the current market. When the UC3843 chip is used in a low input voltage power supply, a soft start circuit is required to reduce the current when the power supply is started. The soft start capacitor cannot discharge in time when the power supply is frequently turned on and turned off, so that the soft start circuit fails when the power supply is frequently turned on and turned off. After the soft start circuit is added, the output setup time is increased, and in order to start normally, the energy supply of the pre-start circuit during the power supply start is required to be increased. There are currently two approaches: one is to reduce the resistance of the starting resistor so that the power consumption of the resistor is multiplied. And secondly, the capacitance value of the VCC capacitor is increased, so that the time from power-on to starting of the power supply is increased.
As shown in fig. 2, the power supply pre-start circuit is composed of a resistor R7 and a capacitor C9, after power is input to VIN, VIN charges C9 through R7, when VCC voltage reaches chip start voltage, the chip works, output starts to be established, because the current of the resistor R7 cannot meet the power supply of the chip, the chip consumes C9 electric quantity, VCC voltage drops, if VCC voltage drops to the power-off VCC voltage, output is established, and the auxiliary winding supplies power to VCC in time. The power supply is normally started, conversely, if the VCC voltage drops to the shutdown VCC voltage, the output is not yet established, the auxiliary winding cannot supply power to the VCC in time, and the power supply fails to start. Because the addition of a soft start circuit increases the output setup time, the chip requires more power at start-up.
SUMMERY OF THE UTILITY MODEL
The utility model discloses the technical problem that needs to solve provides a reducible start capacitor appearance value and makes the soft start circuit of an effectual electric current type pulse width modulator chip all the time at frequent on-off.
In order to solve the above problems, the utility model adopts the following technical proposal:
a soft start circuit of a current type pulse width modulator chip comprises a current type pulse width modulator chip and a soft start circuit, the compensation output pin and the reference output Vref pin of the current type pulse width modulator chip are respectively connected with a soft start circuit, when the current type pulse width modulator chip is started, the compensation output pin of the current type pulse width modulator chip supplies power for the soft start circuit, the soft start circuit stores energy through the energy storage capacitor, after the current mode pulse width modulator chip power supply VCC is powered down and the power supply VCC drops to the chip shutdown voltage, the energy storage capacitor of the soft start circuit supplies power to the current type pulse width modulator chip by referring to the Vref output pin of the current type pulse width modulator chip, so that the current type pulse width modulator chip can still work for a certain time, when the power supply VCC is powered down to a certain voltage below the shutdown voltage of the chip, the energy storage capacitor of the soft start circuit discharges rapidly to prepare for the next start.
Further, the soft start circuit includes diodes D1-D1, resistors R1-R1, capacitors C1-C1, an NMOS Q1, and a transistor Q1, wherein an anode of the diode D1 is connected to a compensation output pin of the current-mode pwm chip, a cathode of the diode D1 is connected to an anode of the capacitor C1, a cathode of the capacitor C1 is grounded, the capacitor C1 is an energy storage capacitor, the resistor R1 is connected in parallel with the diode D1, an anode of the diode D1 is connected to an anode of the capacitor C1, a cathode of the diode D1 is connected to a reference output Vref pin of the current-mode pwm chip, the diode D1 is connected in parallel with the resistor R1, an anode of the diode D1 is connected to a cathode of the diode D1, a cathode of the diode D1 is connected to a gate of the NMOS Q1, a source of the NMOS Q1 is grounded, a drain of the NMOS Q1 is connected to a power supply via the resistor R1, a drain of the NMOS Q1, a base of the transistor Q1 is connected to the transistor Q1, and a collector of the transistor Q1 is, the capacitor C2 is connected in parallel with the gate and source of the NMOS transistor Q1.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:
the utility model discloses soft start circuit gives energy storage capacitor C1 power supply through current type pulse width modulator chip compensation pin, and energy storage capacitor C1 gives the chip power supply through chip Vref pin when the power supply falls the electricity, establishes discharge circuit simultaneously, realizes that the power start is inefficacy not under frequent on & off state, simultaneously, can show and reduce energy storage capacitor and also start the appearance value of electric capacity.
Drawings
Fig. 1 is a schematic circuit diagram of the present invention;
fig. 2 is a schematic diagram of a conventional soft start circuit.
Detailed Description
The utility model is described in further detail below with reference to the attached drawings:
the utility model relates to a soft start circuit that is used for current type pulse width modulator chip (for example: UC3842 UC3843 UC3844 etc.). The utility model discloses a current type pulse width modulator chip and soft start circuit, soft start circuit is connected respectively to the compensation output pin and the reference output Vref pin of current type pulse width modulator chip, when current type pulse width modulator chip starts, the compensation output pin of current type pulse width modulator chip is the power supply of soft start circuit, soft start circuit passes through the energy storage electric capacity energy storage, fall at current type pulse width modulator chip power VCC and the power VCC falls to chip shutdown voltage after, the energy storage electric capacity of soft start circuit passes through current type pulse width modulator chip reference output Vref pin and is its power supply, make current type pulse width modulator chip still can continue to work for a certain time, when the power VCC falls the constant voltage under chip shutdown voltage, the energy storage electric capacity of soft start circuit discharges fast, make the preparation for next start.
As shown in fig. 1, the current-mode pwm chip 3843, the diodes D1-D3, the resistors R1-R5, the capacitors C1-C2, the NMOS Q1, and the transistor Q2, wherein the anode of the diode D1 is connected to a compensation output pin of the current-mode pwm chip, the cathode of the diode D1 is connected to the anode of the capacitor C1, the cathode of the capacitor C1 is grounded, the capacitor C1 is an energy storage capacitor, and the diode D1 and the capacitor C1 implement a soft start function; the resistor R5 is connected with the diode D2 in parallel, the anode of the diode D2 is connected with the anode of the capacitor C1, the cathode of the diode D2 is connected with a reference output Vref pin of the current type pulse width modulator chip, and the introduction of the diode D2 enables the capacitor C1 to supply power to the Vref pin of the chip through the D2 after the power VCC drops to the shutdown voltage of the chip, so that the chip can continue to work for a certain time; diode D3 is connected in parallel with resistor R1, the positive pole of diode D3 is connected with the negative pole of diode D2, the negative pole of diode D3 is connected with the grid of NMOS tube Q1, the source of NMOS tube Q1 is grounded, the drain of NMOS tube Q1 is connected with power VCC through resistor R3, the drain of NMOS tube Q1 is also connected with the base of triode Q2, the emitter of triode Q2 is grounded, the collector of triode Q2 is connected with the positive pole of capacitor C1 through resistor R4, and capacitor C2 is connected in parallel with the grid and the source of NMOS tube Q1.
The working principle is as follows: after 3843 works, pin 1 of 3843 charges capacitor C1 through diode D1, the voltage rises slowly, the PWM duty cycle is gradually expanded, and the soft start effect is achieved.
When the power source VCC is powered down to the shutdown voltage, the energy of the capacitor C1 supplies power to the pin 8 of the UC3843 through the diode D2. The chip can continue to operate when the voltage of the capacitor C1 drops to about 3.5V. The grid voltage of the NMOS transistor Q1 is smaller than Vgs (on), Q1 is turned off, the triode Q2 is turned on, and the capacitor C1 is rapidly discharged through the resistor R4. The soft start circuit is always effective when the power supply is frequently turned on and turned off. The resistor R5 has a large resistance value, and has the function that after the power supply is started, the 8 pins of the resistor 3843 charge the capacitor C1 to 5v through the resistor R5, the voltage is more than 1 pin, and the capacitor C1 is prevented from influencing the loop control of the power supply
The above-mentioned 3843 is UC3843 current mode pulse width modulator chip, to chips such as UC3842 or UC3844, only need to change the parameter of circuit and can realize, do not deviate from the utility model discloses a protection scope.
Claims (2)
1. A soft start circuit of a current mode pulse width modulator chip is characterized in that: the soft start circuit is characterized by comprising a current type pulse width modulator chip and a soft start circuit, wherein a compensation output pin and a reference output Vref pin of the current type pulse width modulator chip are respectively connected with the soft start circuit, when the current type pulse width modulator chip is started, the compensation output pin of the current type pulse width modulator chip supplies power to the soft start circuit, the soft start circuit stores energy through an energy storage capacitor, after a VCC (voltage VCC) of the current type pulse width modulator chip is powered off and the VCC drops to a chip shutdown voltage, the energy storage capacitor of the soft start circuit supplies power to the soft start circuit through the reference output Vref pin of the current type pulse width modulator chip, so that the current type pulse width modulator chip can still work for a certain time, and when the VCC power is powered off to a certain voltage below the chip shutdown voltage, the energy storage capacitor of the soft start circuit discharges rapidly to prepare for next start.
2. A soft start circuit of a current mode pulse width modulator chip as claimed in claim 1, wherein: the soft start circuit comprises diodes D1-D1, resistors R1-R1, capacitors C1-C1, an NMOS tube Q1 and a transistor Q1, wherein the anode of the diode D1 is connected with a compensation output pin of the current type pulse width modulator chip, the cathode of the diode D1 is connected with the anode of the capacitor C1, the cathode of the capacitor C1 is grounded, the capacitor C1 is an energy storage capacitor, the resistor R1 is connected in parallel with the diode D1, the anode of the diode D1 is connected with the anode of the capacitor C1, the cathode of the diode D1 is connected with a reference output Vref pin of the current type pulse width modulator chip, the diode D1 is connected in parallel with the resistor R1, the anode of the diode D1 is connected with the cathode of the diode D1, the cathode of the diode D1 is connected with the gate of the NMOS tube Q1, the source of the NMOS tube Q1 is grounded, the drain of the NMOS tube Q1 is connected with the power supply drain of the transistor Q1 through the resistor R1, the drain of the transistor Q1, the emitter of the transistor Q1, the capacitor C2 is connected in parallel with the gate and source of the NMOS transistor Q1.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201920849717.1U CN209963949U (en) | 2019-06-06 | 2019-06-06 | Soft start circuit of current type pulse width modulator chip |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201920849717.1U CN209963949U (en) | 2019-06-06 | 2019-06-06 | Soft start circuit of current type pulse width modulator chip |
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| CN209963949U true CN209963949U (en) | 2020-01-17 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201920849717.1U Active CN209963949U (en) | 2019-06-06 | 2019-06-06 | Soft start circuit of current type pulse width modulator chip |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114710018A (en) * | 2022-06-06 | 2022-07-05 | 广东东菱电源科技有限公司 | PFC protection circuit for fast startup and shutdown |
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2019
- 2019-06-06 CN CN201920849717.1U patent/CN209963949U/en active Active
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114710018A (en) * | 2022-06-06 | 2022-07-05 | 广东东菱电源科技有限公司 | PFC protection circuit for fast startup and shutdown |
| CN114710018B (en) * | 2022-06-06 | 2022-09-02 | 广东东菱电源科技有限公司 | PFC (power factor correction) protection circuit for quick startup and shutdown |
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