Power supply module hot plug redundant power supply and overcurrent protection circuit

Abstract

The utility model discloses a power supply module hot plug redundant power supply and overcurrent protection circuit, which belongs to the technical field of protection circuits and comprises a first main circuit and a second main circuit which are identical in circuit structure. The first main circuit comprises a first input power supply pulse peak suppression circuit, a first backboard in-place insertion detection circuit, a first output overload detection circuit, a first MOS tube switch circuit, a first output voltage filter circuit and a first output voltage merging circuit which are connected in sequence. According to the utility model, the hot plug design is adopted, the situation of power-on sparking is avoided at the power-on moment, and the soft power-off effect can be realized by pulling out under the condition of no power-off. By adopting the controller with hot plug power limitation and cooperating with the shunt resistor for detecting the current, the input of the pre-stage power supply voltage can be normally switched off under the condition of post-stage short circuit or power over-limit, the post-stage is safe to use, and the condition of overhigh voltage peak caused by surge or the like is solved.

Description

TECHNICAL FIELD

[0001] The utility model relates to protection circuit technical field, concretely relates to a power supply module hot plug redundancy power supply and overcurrent protection circuit. BACKGROUND

[0002] At present, the power supply module mostly uses cold plug, and the application scene is that the control board card takes the direct current through the backboard to supply power for the control board card or the control device, and it has the problems that the power supply cannot be detected when the power supply is short-circuited after striking (contact striking discharge) during plugging, the power supply is unstable, the controller cannot work normally, and the like. The product belongs to an old product, and the discharge phenomenon exists when the plug is replaced, and the contact is easy to be ablated under the condition of the rear stage short circuit; the power supply cannot be inhibited when the power supply is subjected to a sharp voltage; whether the rear stage is short-circuited or overloaded cannot be detected, so that if the rear stage fails, the front stage cannot be disconnected, the rear stage chip generates heat and smokes, and the like; redundancy is not considered, and if the power supply is unstable, the controller cannot work normally, and the like; the power supply output end has not been subjected to a related indication circuit, and the power supply condition cannot be clearly indicated. SUMMARY

[0003] The utility model aims at overcoming the prior art's insufficient, and provides a power supply module hot plug redundancy power supply and overcurrent protection circuit.

[0004] The utility model discloses a purpose is through following technical scheme to realize:

[0005] A power supply module hot plug redundancy power supply and overcurrent protection circuit, including first main circuit and second main circuit, and the circuit structure of first main circuit and second main circuit is same;The first main circuit includes the first input power supply pulse peak suppression circuit, first backboard plug to position detection circuit, first output overload detection circuit, first MOS pipe start switch circuit, first output voltage filter circuit and first output voltage merging circuit that connect gradually.

[0006] Further, the first input power supply pulse peak suppression circuit includes first fuse F1 and first TVS diode D13, one end of first fuse F1 is connected first signal input terminal, and the other end is connected with one end of first TVS diode D13, and the other end of first TVS diode D13 is connected first signal input ground terminal, and the two ends of first TVS diode D13 still are connected first capacitor C177 in parallel.

[0007] Preferably, the first backboard plug-in detection circuit comprises a first controller U45 and a first backboard connector J1, the seventh pin of the first controller U45 is connected with the first signal input ground end after connecting the first resistor R262; the sixth pin of the first controller U45 is connected with the first signal input ground end after connecting the second capacitor C183; the fourth pin of the first controller U45 is connected with the second resistor R259 and the third resistor R264 after connecting the second resistor R259 and the third resistor R264, the other end of the third resistor R264 is connected with the first signal input ground end, the other end of the second resistor R259 is connected with the first backboard connector J1, the third pin of the first controller U45 is connected with the fifth resistor R258 and the fourth resistor R263 after connecting the one end of the fifth resistor R258 and the one end of the fourth resistor R263; the second pin of the first controller U45 is connected with the first backboard connector J1; the eighth pin of the first controller U45 is connected with the sixth resistor R260 and the first output voltage filtering circuit, the ninth pin of the first controller U45 is connected with the first output voltage filtering circuit and the first MOS tube start switch circuit respectively, the fifth pin of the first controller U45 is connected with the first output voltage ground end, and the first controller U45 adopts the LM5069MM-2 / NOPB controller.

[0008] Preferably, the first output overload detection circuit comprises a first shunt resistor R191 connected between the second pin and the first pin of the first controller U45.

[0009] Preferably, the first MOS tube start switch circuit comprises a first MOS tube Q1, the fifth pin, the sixth pin, the seventh pin, the eighth pin and the ninth pin of the first MOS tube Q1 are connected in parallel with the first pin of the first controller U45, the first pin, the second pin and the third pin of the first MOS tube Q1 are connected in parallel with the ninth pin of the first controller U45, and the fourth pin of the first MOS tube Q1 is connected with the tenth pin of the first controller U45.

[0010] Preferably, the first output voltage filtering circuit comprises a first polarity capacitor C178, a second polarity capacitor C179, a second capacitor C181, a third capacitor C180, a seventh resistor R261, a first inductor L20 and a second inductor L21, one end of the first inductor L20 is connected with the first controller U45, the other end of the first inductor L20 is connected with the first output voltage combining circuit, one end of the second inductor L21 is connected with the first controller U45, the other end of the second inductor L21 is connected with the first output voltage ground end, and the first polarity capacitor C178, the second polarity capacitor C179, the second capacitor C181, the third capacitor C180 and the seventh resistor R261 are all connected between the first inductor L20 and the second inductor L21.

[0011] Preferably, the first output voltage merging circuit comprises a third polarized capacitor C176, a fourth capacitor C182 and a first diode D12, one end of the third polarized capacitor C176 is connected between the first inductor L20 and the first diode D12, the other end of the third polarized capacitor C176 is connected to the first output voltage ground end, one end of the fourth capacitor C182 is connected between the third polarized capacitor C176 and the first diode D12 and is connected to the first signal input test end, a first test point TP105 is further arranged between the fourth capacitor C182 and the first diode D12, the other end of the first diode D12 is connected to the first output signal end, a second test point TP89 is arranged between the first diode D12 and the first output signal end, the other end of the fourth capacitor C182 is connected to the first output voltage ground end, and a third test point TP90 is arranged between the other end of the fourth capacitor C182 and the first output voltage ground end.

[0012] Preferably, the first output voltage merging circuit comprises a third polarized capacitor C176, a fourth capacitor C182 and a first diode D12, one end of the third polarized capacitor C176 is connected between the first inductor L20 and the first diode D12, the other end of the third polarized capacitor C176 is connected to the first output voltage ground end, one end of the fourth capacitor C182 is connected between the third polarized capacitor C176 and the first diode D12 and is connected to the first signal input test end, a first test point TP105 is further arranged between the fourth capacitor C182 and the first diode D12, the other end of the first diode D12 is connected to the first output signal end, a second test point TP89 is arranged between the first diode D12 and the first output signal end, the other end of the fourth capacitor C182 is connected to the first output voltage ground end, and a third test point TP90 is arranged between the other end of the fourth capacitor C182 and the first output voltage ground end.

[0013] The utility model discloses the beneficial effect is:

[0014] 1) the utility model discloses the hot plug design, the power-on moment has eliminated the power-on spark occurrence, and the effect of soft power-off can be realized under the condition of not power-off.

[0015] 2) the utility model discloses the shunt resistance of "LM5069MM-2 / NOPB controller with hot plug power limit" cooperation detection current, effectively solved the situation of the normal shutdown of the input of the front stage power supply voltage under the condition of the short circuit or power overrun of the rear stage, and the rear stage can be safe.

[0016] 3) the utility model discloses the fuse + TVS diode mode of power input measurement design, effectively solved the situation of the damage of the rear stage electric appliance caused by the surge or other causes of voltage peak too high.

[0017] 4) the utility model discloses two-way redundant power input design, effectively solved the situation of the unstable supply output end caused by the unstable voltage of a certain power supply. Greatly increase the stability of output voltage.

[0018] 5) the utility model discloses the indication of the work of the power supply of the front stage 2 input indication and rear stage output indication can be clearly indicated.

[0019] 6)The utility model discloses a test point TP105, TP89, TP106, TP191;Therefore can conveniently test input and output voltage value. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 For the structure diagram of the power supply module hot plug redundant power supply and overcurrent protection circuit of the utility model embodiment;

[0021] Figure 2 For the signal path schematic diagram of the power supply module hot plug redundant power supply and overcurrent protection circuit of the utility model embodiment. DETAILED DESCRIPTION

[0022] The technical scheme of the utility model will be described below in conjunction with embodiments, apparently, the described embodiments are only part of the embodiments of the utility model, not all the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by the person skilled in the art without creative labor belong to the protection scope of the utility model.

[0023] In order to solve the discharge phenomenon when replacing the plug-in power module, the ablation contact condition under the condition of short circuit of the rear stage, the condition that the input power peak voltage cannot be effectively suppressed, the condition that the rear stage composition chip is damaged by heating and smoking when the power supply load end is short-circuited or heavily loaded, the condition that the power supply unstable controller does not work normally, the condition that the power supply input and output end indication is not clear, the utility model proposes a power supply module hot plug redundant power supply and overcurrent protection circuit, its structure schematic diagram as shown in Figure 1 Including first main circuit and second main circuit, the circuit structure of first main circuit and second main circuit is same;The first main circuit includes first input power pulse peak suppression circuit, first backboard insertion position detection circuit, first output overload detection circuit, first MOS tube start switch circuit, first output voltage filter circuit and first output voltage merging circuit that connect gradually, the signal path schematic diagram of the utility model as shown in Figure 2

[0024] ​Specifically, the first input power supply pulse peak suppression circuit includes a first fuse F1 and a first TVS diode D13, one end of the first fuse F1 is connected to the first signal input end, the other end is connected to one end of the first TVS diode D13, the other end of the first TVS diode D13 is connected to the first signal input ground end, and the two ends of the first TVS diode D13 are also connected in parallel with the first capacitor C177. The input signal +24V_IN1 of the first signal input end first passes through the first fuse F1 and then passes through the first TVS diode D13, and finally outputs the signal to the first signal input ground end GND_IN1. In this embodiment, the first fuse F1 uses a 1206THWR fuse, and the first TVS diode D13 uses an SMCJ24CA TVS diode.

[0025] Specifically, the first backplane insertion detection circuit includes a first controller U45 and a first backplane connector J1. The seventh pin of the first controller U45 is connected to the first signal input ground end after being connected to the first resistor R262; the sixth pin of the first controller U45 is connected to the first signal input ground end after being connected to the second capacitor C183; the second resistor R259 and the third resistor R264 are connected to the fourth pin of the first controller U45 after being connected to each other, the other end of the third resistor R264 is connected to the first signal input ground end, and the other end of the second resistor R259 is connected to the first backplane connector J1. The first resistor R263 and the fifth resistor R258 are connected to the third pin of the first controller U45 after being connected to each other; the second pin of the first controller U45 is connected to the first backplane connector J1; the eighth pin of the first controller U45 is connected to the first output voltage filtering circuit after being connected to the sixth resistor R260; the ninth pin of the first controller U45 is connected to the first output voltage filtering circuit and the first MOS tube starting circuit respectively; and the fifth pin of the first controller U45 is connected to the first output voltage ground end. The first controller U45 adopts an LM5069MM-2 / NOPB controller, which has a hot plug power limiting function. The input signal +24V_IN1 first passes through the first fuse F1 (1206THWR fuse), then passes through the first backplane connector J1 (backplane short circuit line) and the fifth resistor R258 in sequence, and finally reaches the third pin of the first controller U45 (LM5069MM-2 / NOPB controller with hot plug power limiting function). The input signal +24V_IN1 first passes through the first fuse F1 (1206THWR fuse), then passes through the first backplane connector J1 (backplane short circuit line) and the second resistor R259 in sequence, and finally reaches the fourth pin of the first controller U45 (LM5069MM-2 / NOPB controller with hot plug power limiting function).

[0026] Specifically, the first output overload detection circuit includes a first shunt resistor R191 (0.05R / 3W), which is connected between the second pin and the first pin of the first controller U45. One end of the first shunt resistor R191 is connected to the second pin of the first controller U45 (LM5069MM-2 / NOPB controller with hot plug power limit), and the other end is connected to the first pin of the first controller U45.

[0027] Specifically, the first MOS switch circuit includes a first MOS Q1, the fifth pin, the sixth pin, the seventh pin, the eighth pin, and the ninth pin of the first MOS Q1 are connected in parallel to the first pin of the first controller U45, the first pin, the second pin, and the third pin of the first MOS Q1 are connected in parallel to the ninth pin of the first controller U45, the fourth pin of the first MOS Q1 is connected to the tenth pin of the first controller U45, and the first MOS Q1 uses an FDMS86101 MOS.

[0028] Specifically, the first output voltage filter circuit includes a first polar capacitor C178, a second polar capacitor C179, a second capacitor C181, a third capacitor C180, a seventh resistor R261, a first inductor L20, and a second inductor L21, one end of the first inductor L20 is connected to the first controller U45, the other end of the first inductor L20 is connected to the first output voltage merging circuit, one end of the second inductor L21 is connected to the first controller U45, the other end of the second inductor L21 is connected to the first output voltage ground end, the first polar capacitor C178, the second polar capacitor C179, the second capacitor C181, the third capacitor C180, and the seventh resistor R261 are all connected between the first inductor L20 and the second inductor L21, and the first inductor L20 and the second inductor L21 use MPZ2012S101AT000 inductors.

[0029] Specifically, the first output voltage combining circuit includes a third polarized capacitor C176, a fourth capacitor C182, and a first diode D12. One end of the third polarized capacitor C176 is connected between the first inductor L20 and the first diode D12, and the other end of the third polarized capacitor C176 is connected to the first output voltage ground end. One end of the fourth capacitor C182 is connected between the third polarized capacitor C176 and the first diode D12, and is connected to the first signal input test end. A first test point TP105 is further arranged between the fourth capacitor C182 and the first diode D12. The other end of the first diode D12 is connected to the first output signal end, and a second test point TP89 is arranged between the first diode D12 and the first output signal end. The other end of the fourth capacitor C182 is connected to the first output voltage ground end, and a third test point TP90 is arranged between the other end of the fourth capacitor C182 and the first output voltage ground end. The first output voltage ground end outputs a signal +24V_GND. The signal first passes through the third test point TP90, the fourth capacitor C182, and the third polarized capacitor C176 in sequence, and then passes through the first test point TP105, the first diode D12, and the second test point TP89 to the first output signal end to output a +24V signal. The input signal +24V_IN1 first passes through the first fuse F1 (1206THWR fuse), the first shunt resistor R191 (shunt resistor), and then passes through the first MOS tube and the first inductor L20, and finally passes through the first diode D12 to the first output signal end to output a +24V signal. In this embodiment, the first MOS tube uses an FDMS86101 MOS tube, the first inductor L20 uses an MPZ2012S101AT000 filter inductor, and the first diode D12 uses an MBRS340T3G diode.

[0030] Specifically, the first output voltage combining circuit includes a third polarized capacitor C176, a fourth capacitor C182, and a first diode D12. One end of the third polarized capacitor C176 is connected between the first inductor L20 and the first diode D12, and the other end of the third polarized capacitor C176 is connected to the first output voltage ground end. One end of the fourth capacitor C182 is connected between the third polarized capacitor C176 and the first diode D12, and is connected to the first signal input test end. A first test point TP105 is further arranged between the fourth capacitor C182 and the first diode D12. The other end of the first diode D12 is connected to the first output signal end, and a second test point TP89 is arranged between the first diode D12 and the first output signal end. The other end of the fourth capacitor C182 is connected to the first output voltage ground end, and a third test point TP90 is arranged between the other end of the fourth capacitor C182 and the first output voltage ground end. The first output voltage ground end outputs a signal +24V_GND. The signal first passes through the third test point TP90, the fourth capacitor C182, and the third polarized capacitor C176 in sequence, and then passes through the first test point TP105, the first diode D12, and the second test point TP89 to the first output signal end to output a +24V signal. The input signal +24V_IN1 first passes through the first fuse F1 (1206THWR fuse), the first shunt resistor R191 (shunt resistor), and then passes through the first MOS tube and the first inductor L20, and finally passes through the first diode D12 to the first output signal end to output a +24V signal. In this embodiment, the first MOS tube uses an FDMS86101 MOS tube, the first inductor L20 uses an MPZ2012S101AT000 filter inductor, and the first diode D12 uses an MBRS340T3G diode.

[0031] Specifically, the second main circuit comprises, in sequence, a second input power supply pulse peak suppression circuit, a second backboard plug-in position detection circuit, a second output overload detection circuit, a second MOS tube starting switch circuit, a second output voltage filtering circuit and a second output voltage merging circuit. The second input power supply pulse peak suppression circuit specifically comprises a second fuse F2 and a second TVS diode D15. The second backboard plug-in position detection circuit specifically comprises a second controller U46, a second backboard connector J2, a fifth capacitor C185, an eleventh resistor R270, a twelfth capacitor C191, a twelfth resistor R267, a thirteenth resistor R272, a fourteenth resistor R271, a fifteenth resistor R266 and a sixteenth resistor R268. The second MOS tube starting switch circuit comprises a second MOS tube Q2. The second output overload detection circuit comprises a second shunt resistor R265. The second output voltage filtering circuit comprises a fourth polar capacitor C186, a fifth polar capacitor C187, a sixth capacitor C189, a seventh capacitor C188, a seventeenth resistor R269, a third inductor L22 and a fourth inductor L23. The second output voltage merging circuit comprises a sixth polar capacitor C184, an eighth capacitor C182 and a second diode D12. A fourth test point TP106, a fifth test point TP91, a second output voltage ground end, a second output signal end and a second signal input test end are further arranged on the second output voltage merging circuit. A first signal input ground end and a first signal input end are further arranged on the second input power supply pulse peak suppression circuit.

[0032] Specifically, the second main circuit further comprises a second output indication loop. The second signal input test end is connected with the second output voltage ground end through the second output indication loop. The second output indication loop comprises, in sequence, an eighteenth resistor R589 and a third indication lamp HL17 connected in series.

[0033] Specifically, the first main circuit channel +24V_IN2 main input and output channel peak suppression circuit. +24V_IN2 through F2 (1206THWR fuse), through D15 (SMCJ24CA TVS diode) to GND_IN2. +24V_IN2 through F2 (1206THWR fuse), through J2 (backplane short circuit line) through resistor R266 to the third pin of U46 (LM5069MM-2 / NOPB controller with hot plug power limiting). +24V_IN2 through F2 (1206THWR fuse), through J2 (backplane short circuit line) through resistor R267 to the fourth pin of U46 (LM5069MM-2 / NOPB controller with hot plug power limiting). +24V_IN1 through F2 (1206THWR fuse) through R265 (shunt resistor), through Q2 (FDMS86101 MOS tube) through L22 (MPZ2012S101AT000 filter inductance) through D14 (MBRS340T3G diode) to output +24V. One end of resistor R265 is connected with the second pin of U46 (LM5069MM-2 / NOPB controller with hot plug power limiting), and the other end of resistor R265 is connected with the first pin of U46. +24V_GND through C190, C184, through TP106 (test point), through D14 (diode), through TP91 (test point) to +24V. The structure of the first main circuit and the second main circuit is completely identical, and excessive details are not described here.

[0034] Specifically, the utility model provides a kind of power supply module hot plug redundancy power supply and overcurrent protection circuit;With point plug-in function and plug-in in-place detection function using hot plug design;With the function of preventing the output of the rear stage from being burnt by short circuit or overload of the rear stage;With the function of protecting the rear stage from being damaged by surge or other causes of voltage peak too high;With two-way redundant power supply input design, increase the stability function of output voltage.Input and output voltage indicating lamp is provided with, can clearly indicate the function of input voltage;With input and output voltage test point, facilitate debugging and testing.

[0035] The above is only the preferred embodiment of the utility model, and it should be understood that the utility model is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein by the above teaching or related technical or knowledge. The modification and change made by the person skilled in the art without departing from the spirit and scope of the utility model should be within the protection scope of the claims attached to the utility model.

Claims

1. A hot plug redundant power supply module, power supply and over current protection circuit, characterized in that, The first main circuit and the second main circuit have the same circuit structure; the first main circuit comprises a first input power supply pulse peak suppression circuit, a first backboard insertion position detection circuit, a first output overload detection circuit, a first MOS tube starting switch circuit, a first output voltage filtering circuit and a first output voltage merging circuit connected in sequence.

2. The hot plug redundant power supply and over current protection circuit of claim 1, wherein: The first input power supply pulse peak suppression circuit comprises a first fuse F1 and a first TVS diode D13, one end of the first fuse F1 is connected to a first signal input end, the other end is connected to one end of the first TVS diode D13, the other end of the first TVS diode D13 is connected to a first signal input ground end, and the two ends of the first TVS diode D13 are also connected in parallel with a first capacitor C177.

3. The hot plug redundant power supply and over current protection circuit of claim 2, wherein: The first backboard insertion position detection circuit comprises a first controller U45 and a first backboard connector J1, the seventh pin of the first controller U45 is connected to the first signal input ground end after passing through a first resistor R262; the sixth pin of the first controller U45 is connected to the first signal input ground end after passing through a second capacitor C183; one end of a second resistor R259 and one end of a third resistor R264 are connected to the fourth pin of the first controller U45, the other end of the third resistor R264 is connected to the first signal input ground end, the other end of the second resistor R259 is connected to the first backboard connector J1, one end of a fourth resistor R263 and one end of a fifth resistor R258 are connected to the third pin of the first controller U45; the second pin of the first controller U45 is connected to the first backboard connector J1; the eighth pin of the first controller U45 is connected to the first output voltage filtering circuit after passing through a sixth resistor R260, the ninth pin of the first controller U45 is connected to the first output voltage filtering circuit and the first MOS tube starting switch circuit respectively, the fifth pin of the first controller U45 is connected to a first output voltage ground end, and the first controller U45 adopts an LM5069MM-2 / NOPB controller.

4. The hot plug redundant power supply and over current protection circuit of claim 3, wherein: The first output overload detection circuit comprises a first shunt resistor R191 connected between the second pin and the first pin of the first controller U45.

5. The hot plug redundant power supply and over current protection circuit of claim 4, wherein: The first MOS tube starting switch circuit comprises a first MOS tube Q1, the fifth pin, the sixth pin, the seventh pin, the eighth pin and the ninth pin of the first MOS tube Q1 are connected in parallel to the first pin of the first controller U45, the first pin, the second pin and the third pin of the first MOS tube Q1 are connected in parallel to the ninth pin of the first controller U45, and the fourth pin of the first MOS tube Q1 is connected to the tenth pin of the first controller U45.

6. The hot plug redundant power supply and over current protection circuit of claim 5, wherein: The first output voltage filter circuit comprises a first polarized capacitor C178, a second polarized capacitor C179, a second capacitor C181, a third capacitor C180, a seventh resistor R261, a first inductor L20 and a second inductor L21, one end of the first inductor L20 is connected with the first controller U45, the other end of the first inductor L20 is connected with the first output voltage combining circuit, one end of the second inductor L21 is connected with the first controller U45, the other end of the second inductor L21 is connected with the first output voltage ground end, and the first polarized capacitor C178, the second polarized capacitor C179, the second capacitor C181, the third capacitor C180 and the seventh resistor R261 are all connected between the first inductor L20 and the second inductor L21.

7. The hot plug redundant power supply and over current protection circuit of claim 6, wherein: The first output voltage combining circuit comprises a third polarized capacitor C176, a fourth capacitor C182 and a first diode D12, one end of the third polarized capacitor C176 is connected between the first inductor L20 and the first diode D12, the other end of the third polarized capacitor C176 is connected with the first output voltage ground end, one end of the fourth capacitor C182 is connected between the third polarized capacitor C176 and the first diode D12 and is connected with the first signal input test end, a first test point TP105 is further arranged between the fourth capacitor C182 and the first diode D12, the other end of the first diode D12 is connected with the first output signal end, a second test point TP89 is arranged between the first diode D12 and the first output signal end, the other end of the fourth capacitor C182 is connected with the first output voltage ground end, and a third test point TP90 is arranged between the other end of the fourth capacitor C182 and the first output voltage ground end.

8. The hot plug redundant power supply and over current protection circuit of claim 7, wherein: The first output voltage filter circuit further comprises a first output indication loop and a first input indication loop, the first signal input test end is connected with the first output voltage ground end through the first output indication loop, the first output indication loop comprises an eighth resistor R588 and a first indication lamp HL16 connected in series; the first output signal end is connected with the first output voltage ground end through the first input indication loop, and the first input indication loop comprises a ninth resistor R590 and a second indication lamp HL18 connected in series.

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