A surge suppression circuit suitable for low temperature startup

Abstract

The present invention discloses a surge suppression circuit suitable for low-temperature startup, including a rectifier bridge, a voltage sampling unit, a delay unit, a self-locking unit, and a linear regulator. The input AC power outputs a DC power supply through the rectifier bridge, and the DC power supply charges the first capacitor through a thermistor. A relay is connected in parallel at both ends of the thermistor. The voltage sampling unit dynamically detects the voltage at both ends of the thermistor and performs differential amplification and output of the voltage at both ends of the thermistor. The delay unit is arranged between the voltage sampling unit and the self-locking unit, and the self-locking unit is connected to the relay. The linear regulator is connected to the rectifier bridge, and the DC power output by the rectifier bridge is converted into the power supply voltage of the relay and the voltage sampling unit through the linear regulator. The present invention improves the low-temperature startup capability and the relay response speed at the same time, especially when the resistance value of the low-temperature thermistor becomes larger, the thermistor will not be damaged due to long-term work.

Description

Technical Field

[0001] The invention relates to a surge suppression circuit, in particular to a surge suppression circuit suitable for low-temperature startup. Background Art

[0002] At present, surge suppression circuits for low-power power supplies all use thermistors to suppress startup surge current. The surge current specifications of existing products are relatively large. In order to improve the competitiveness of products, the startup surge current must be less than 10A when the input is 230V AC. Therefore, a thermistor with a larger resistance is needed to suppress it. In this way, the thermistor will have a large loss when the machine is turned on and off continuously at low temperatures, and there is a risk of damage. At the same time, because the thermistor has a negative temperature coefficient, the resistance value increases at low temperatures, the voltage divider increases, and the undervoltage protection or overload protection (OLP) of the chip is triggered, causing the product to fail to start normally.

[0003] like Figure 5 As shown in the figure, the commonly used surge suppression method is to bypass the thermistor only after the input voltage is turned on and the power supply VCC reaches the rated value. This control method has a long response time and will cause a large loss in the thermistor during the period from the input voltage to the resistor being bypassed. At low temperatures, the capacitance will decrease. If the low-temperature and low-voltage 90V AC power is input, the voltage drop on the thermistor will be higher, and the voltage drop on the capacitor C1 will be lower, that is, the capacitor is not fully charged, which will first trigger the undervoltage protection or overload protection (OLP) of the chip, the power supply VCC cannot be established, and the relay will keep jumping, causing the product to fail to start normally.

[0004] like Figure 6 As shown, there is also a method of sampling the bulk capacitor voltage using a voltage regulator or an operational amplifier, and closing the relay after reaching a preset value. This method can only be used for a fixed input voltage, such as inputting 230V AC to preset the bulk capacitor voltage. Because the voltage regulator or operational amplifier requires a fixed reference voltage, such as 2.5V, the preset voltage value of the bulk capacitor is also difficult to change with the range of AC input. When 90V AC is input, the relay is set to be closed after the capacitor is fully charged, but when 230V AC is input, the relay will be closed half in advance when the voltage is equivalent to 90V AC, thereby generating a larger surge current, and the purpose of suppressing the surge current cannot be achieved. Therefore, this method is subject to the influence of the input voltage and is only suitable for models with fixed input voltage, and has certain limitations.

[0005] Therefore, it is necessary to design a dynamic detection circuit that can reduce the startup surge current and can also start up normally at a low temperature of -40℃. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a surge suppression circuit suitable for low-temperature startup. Compared with conventional surge circuits, the low-temperature startup capability is improved, and the relay response speed is also improved. Especially when the resistance of the low-temperature thermistor becomes larger, the thermistor will not be at risk of damage due to long-term operation.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a surge suppression circuit suitable for low-temperature startup includes a rectifier bridge, a voltage sampling unit, a delay unit, a self-locking unit, and a linear regulator. The input AC power outputs a DC power supply through the rectifier bridge, and the DC power supply charges the first capacitor through a thermistor. A relay is connected in parallel at both ends of the thermistor. The voltage sampling unit dynamically detects the voltage at both ends of the thermistor and differentially amplifies and outputs the voltage at both ends of the thermistor. The delay unit is arranged between the voltage sampling unit and the self-locking unit. The self-locking unit is connected to the relay. The self-locking unit is used to lock the high level output by the voltage sampling unit, and the relay is turned on after the delay unit extends the relay pull-in time so that the relay is pulled in. The linear regulator is connected to the rectifier bridge, and the DC power output by the rectifier bridge is converted into the power supply voltage of the relay and the voltage sampling unit through the linear regulator.

[0008] As a preferred solution, the voltage sampling unit includes an operational amplifier, a first resistor is connected in series between the negative input terminal of the operational amplifier and the input terminal of the thermistor, a node V1 is connected in series between the first resistor and the negative input terminal of the operational amplifier and then connected to ground, a second resistor is connected in series between the positive input terminal of the operational amplifier and the output terminal of the thermistor, a node V2 is connected in series between the second resistor and the positive input terminal of the operational amplifier and then connected to ground.

[0009] As a preferred solution, a sixth resistor is connected in series between the first resistor and the negative input terminal of the operational amplifier, and a fifth resistor is connected in series between the second resistor and the positive input terminal of the operational amplifier.

[0010] As a preferred solution, the delay unit includes a seventh resistor and a second capacitor, and the output end of the operational amplifier is connected in series with the seventh resistor and the second capacitor and then grounded.

[0011] As a preferred scheme, a first voltage zener diode and a second unidirectional diode are connected in series between the output end of the operational amplifier and the seventh resistor, the output end of the first voltage zener diode is connected to the input end of the operational amplifier, the input end of the first voltage zener diode is connected to the input end of the second unidirectional diode, and the output end of the second unidirectional diode is connected to the seventh resistor.

[0012] As a preferred solution, the self-locking unit includes a first transistor and a second transistor, the collector of the first transistor is connected to the base of the second transistor and the lead-out node is connected between the seventh resistor and the second capacitor, the base of the first transistor is connected to the collector of the second transistor and the lead-out node is connected in series with the ninth resistor and then connected to the relay, the emitter of the first transistor is connected in series with the eighth resistor and then connected to the relay, and the emitter of the second transistor is grounded.

[0013] As a preferred solution, the input end of the linear regulator is connected to the positive output end of the rectifier bridge, and the output end of the linear regulator is connected in series with a third unidirectional diode to output a supply voltage, which provides power for the relay and the operational amplifier.

[0014] Compared with the prior art, the present invention has the following beneficial effects: the present invention uses an operational amplifier to dynamically detect the voltage across the thermistor (NTC), differentially amplifies the front and rear ends of the thermistor (NTC), and when the bulk capacitor is fully charged, the input current drops rapidly, the operational amplifier operates to output a relay drive signal, and the relay is energized. The present invention has a dynamic adaptive input voltage characteristic, and can accurately detect the charging state of the bulk capacitor under all input voltage conditions, accurately control the relay action, effectively reduce the input surge current, and is suitable for a wide range of inputs, while also improving the low-temperature startup characteristics of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a circuit schematic diagram of the present invention;

[0016] Figure 2 It is a working timing diagram of the present invention;

[0017] Figure 3 This is a waveform diagram of the present invention when the power is turned on without adding a surge suppression circuit adapted to low temperature power-on;

[0018] Figure 4 It is a waveform diagram of a surge suppression circuit suitable for low-temperature startup when the present invention is turned on;

[0019] Figure 5 It is a commonly used surge suppression circuit diagram in the prior art;

[0020] Figure 6 It is another commonly used surge suppression circuit diagram in the prior art. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention.

[0022] Example:

[0023] like Figure 1 As shown, a surge suppression circuit suitable for low-temperature startup includes a rectifier bridge BD1, a voltage sampling unit, a delay unit, a self-locking unit, and a linear regulator LDO. The input AC power outputs a DC power supply through the rectifier bridge BD1, and the DC power supply charges the first capacitor C1 through the thermistor RTH1. The two ends of the thermistor RTH1 are connected in parallel with a relay RELAY. The voltage sampling unit dynamically detects the voltage across the thermistor RTH1 and performs differential amplification and output of the voltage across the thermistor RTH1. The delay unit is arranged between the voltage sampling unit and the self-locking unit. The self-locking unit is connected to the relay RELAY. The self-locking unit is used to lock the high level output by the voltage sampling unit. After the delay unit extends the relay RELAY pull-in time, it is turned on to make the relay RELAY pull-in. The linear regulator LDO is connected to the rectifier bridge BD1. The DC power output by the rectifier bridge BD1 is converted into the power supply voltage VCC of the relay RELAY and the voltage sampling unit through the linear regulator LDO.

[0024] Specifically, the connection terminal ACL and the connection terminal ACN are used to receive the input of the alternating current, the connection terminal ACL and the connection terminal ACN are respectively connected to the two input ends of the rectifier bridge BD1, the positive output end of the rectifier bridge BD1 is connected in series with the thermistor RTH1 and the first capacitor C1 and then grounded, and the negative output end of the rectifier bridge BD1 is grounded.

[0025] Preferably, the voltage sampling unit includes an operational amplifier U1, a first resistor R1 is connected in series between the negative input terminal of the operational amplifier U1 and the input terminal of the thermistor RTH1, a node V1 is derived between the first resistor R1 and the negative input terminal of the operational amplifier U1, a third resistor R3 is connected in series and then grounded, a second resistor R2 is connected in series between the positive input terminal of the operational amplifier U1 and the output terminal of the thermistor RTH1, a node V2 is derived between the second resistor R2 and the positive input terminal of the operational amplifier U1, a fourth resistor R4 is connected in series and then grounded.

[0026] Specifically, the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 play a voltage dividing role, wherein the first resistor R1 and the third resistor R3 divide the voltage of the input end of the thermistor RTH1, and the second resistor R2 and the fourth resistor R4 divide the voltage of the output end of the thermistor RTH1.

[0027] More specifically, the operational amplifier U1 uses the voltage across the thermistor RTH1. When the power is turned on, the first capacitor C1 has no charge storage, so the first capacitor C1 will be charged, thereby generating a voltage difference across the thermistor RTH1. The operational amplifier U1 outputs a high level after the voltage of the node V2 sampled by the operational amplifier U1 is greater than the voltage of the sampled node V1.

[0028] More preferably, a sixth resistor R6 is connected in series between the first resistor R1 and the negative input terminal of the operational amplifier U1 , and a fifth resistor R5 is connected in series between the second resistor R2 and the positive input terminal of the operational amplifier U1 .

[0029] Specifically, the fifth resistor R5 and the sixth resistor R6 play a role in current limiting.

[0030] Preferably, the delay unit comprises a seventh resistor R7 and a second capacitor C2, and the output end of the operational amplifier U1 is connected in series with the seventh resistor R7 and the second capacitor C2 and then grounded.

[0031] Specifically, the delay unit is used to allow the first capacitor C1 to be charged to about 90%.

[0032] More preferably, a first voltage zener diode D1 and a second unidirectional diode D2 are connected in series between the output end of the operational amplifier U1 and the seventh resistor R7, the output end of the first voltage zener diode D1 is connected to the input end of the operational amplifier U1, the input end of the first voltage zener diode D1 is connected to the input end of the second unidirectional diode D2, and the output end of the second unidirectional diode D2 is connected to the seventh resistor R7.

[0033] Specifically, the operational amplifier U1 outputs a high level, which is stepped down by the first voltage-stabilizing diode D1 and then delayed for a period of time by the seventh resistor R7 and the second capacitor C2. Then, the self-locking unit is turned on, so that the relay RELAY is energized and the thermistor RTH1 is bypassed.

[0034] Preferably, the self-locking unit includes a first transistor Q1 and a second transistor Q2, the collector of the first transistor Q1 is connected to the base of the second transistor Q2 and the lead-out node is connected between the seventh resistor R7 and the second capacitor C2, the base of the first transistor Q1 is connected to the collector of the second transistor Q2 and the lead-out node is connected in series with the ninth resistor R9 and then connected to the relay RELAY, the emitter of the first transistor Q1 is connected in series with the eighth resistor R8 and then connected to the relay RELAY, and the emitter of the second transistor Q2 is grounded.

[0035] Specifically, after power-on, the surge will continue to oscillate for several cycles due to the parasitic capacitance and inductance in the circuit, causing the output of the operational amplifier U1 to switch between high and low levels, that is, the relay RELAY will jump when it is energized or disconnected. After adding a self-locking circuit, a high-level signal can be locked and will not be affected by the oscillating waveform at both ends of the thermistor RTH1.

[0036] Preferably, the input end of the linear regulator LDO is connected to the positive output end of the rectifier bridge BD1, and the output end of the linear regulator LDO is connected in series with a third unidirectional diode D3 to output a power supply voltage VCC, which provides power for the relay RELAY and the operational amplifier U1.

[0037] Specifically, Figure 2 As shown in the working sequence, the operational amplifier U1 is used to sample the voltage across the thermistor RTH1. When the power is turned on, the first capacitor C1 has no charge storage, so the first capacitor C1 will be charged, thereby generating a voltage difference across the thermistor RTH1. The voltage of the node V2 sampled by the operational amplifier U1 is greater than the voltage of the sampled node V1, and a high level is output. After the first voltage-stabilizing diode D1 steps down the voltage, the seventh resistor R7 and the second capacitor C2 are used to delay for a period of time, and then the second transistor Q2 in the self-locking circuit is turned on, so that the relay RELAY is energized to bypass the thermistor RTH1.

[0038] The circuit of the present invention can dynamically adjust the relay RELAY pull-in time through the voltage across the thermistor RTH1. The time needs to be controlled so that the charging voltage of the first capacitor C1 reaches more than 90% of the input voltage peak value before the relay RELAY is pulled in. Figure 3 , Figure 4 By comparison, it can be seen that after the relay RELAY is actuated, the thermistor RTH1 is bypassed, and the voltage V_RTH across the thermistor RTH1 is 0, where the blue waveform is the voltage V_RTH across the thermistor RTH1, the red waveform is the input current I_in, the green waveform is the power supply voltage Vbus, and the yellow waveform is the power supply voltage VCC.

[0039] In summary, compared with the conventional surge solution, the present invention improves the low-temperature startup capability and at the same time improves the response speed of the relay RELAY, and will not cause the thermistor RTH1 to be damaged due to long-term operation, especially when the resistance of the low-temperature thermistor RTH1 becomes larger.

[0040] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A surge suppression circuit suitable for low temperature startup, characterized by: The invention comprises a rectifier bridge, a voltage sampling unit, a delay unit, a self-locking unit and a linear regulator. The input AC power outputs a DC power through the rectifier bridge. The DC power charges a first capacitor through a thermistor. A relay is connected in parallel at both ends of the thermistor. The voltage sampling unit dynamically detects the voltage at both ends of the thermistor and performs differential amplification and output of the voltage at both ends of the thermistor. The delay unit is arranged between the voltage sampling unit and the self-locking unit. The self-locking unit is connected to the relay. The self-locking unit is used to lock the high level output by the voltage sampling unit. After the delay unit prolongs the relay pull-in time, the relay is turned on to pull in. The linear regulator is connected to the rectifier bridge. The DC power output by the rectifier bridge is converted into the power supply voltage of the relay and the voltage sampling unit through the linear regulator.

2. The surge suppression circuit adapted to low temperature startup according to claim 1, characterized in that: The voltage sampling unit includes an operational amplifier, a first resistor is connected in series between the negative input terminal of the operational amplifier and the input terminal of the thermistor, a node V1 is connected in series between the first resistor and the negative input terminal of the operational amplifier and then connected to ground, a second resistor is connected in series between the positive input terminal of the operational amplifier and the output terminal of the thermistor, a node V2 is connected in series between the second resistor and the positive input terminal of the operational amplifier and then connected to ground.

3. The surge suppression circuit adapted to low temperature startup according to claim 2, characterized in that: A sixth resistor is connected in series between the first resistor and the negative input terminal of the operational amplifier, and a fifth resistor is connected in series between the second resistor and the positive input terminal of the operational amplifier.

4. The surge suppression circuit adapted to low temperature startup according to claim 2, characterized in that: The delay unit includes a seventh resistor and a second capacitor. The output end of the operational amplifier is connected in series with the seventh resistor and the second capacitor and then grounded.

5. The surge suppression circuit adapted to low temperature startup according to claim 4, characterized in that: A first voltage zener diode and a second unidirectional diode are connected in series between the output end of the operational amplifier and the seventh resistor, the output end of the first voltage zener diode is connected to the input end of the operational amplifier, the input end of the first voltage zener diode is connected to the input end of the second unidirectional diode, and the output end of the second unidirectional diode is connected to the seventh resistor.

6. The surge suppression circuit adapted to low temperature startup according to claim 4, characterized in that: The self-locking unit includes a first transistor and a second transistor, the collector of the first transistor is connected to the base of the second transistor and the lead-out node is connected between the seventh resistor and the second capacitor, the base of the first transistor is connected to the collector of the second transistor and the lead-out node is connected in series with the ninth resistor and then connected to the relay, the emitter of the first transistor is connected in series with the eighth resistor and then connected to the relay, and the emitter of the second transistor is grounded.

7. The surge suppression circuit adapted to low temperature startup according to claim 6, characterized in that: The input end of the linear regulator is connected to the positive output end of the rectifier bridge, and the output end of the linear regulator is connected in series with a third unidirectional diode to output a supply voltage, which provides power for the relay and the operational amplifier.

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