稳压芯片并联的问题

一、前言

如果一个稳压芯片输出电流不能够满足要求，是否可以简单的将两个稳压芯片进行并联提供更大的输出电流呢？ 下面简单测试一下，看会出现什么问题。

二、测试电路

设计两路稳压芯片并联电路。这里给出了两路独立的稳压芯片 7805。它们的输出可以并联在一起，为负载提供输出电流。输入分开，由不同的直流电源提供工作电流，也间接获得每个稳压器的工作电流。下面也设计了 1117 ，3.3V的稳压芯片。该电路板也可以对1117 稳压芯片进行测试。使用单面板制作测试电路。

一分钟之后获得测试电路板。检查一下制作的情况。非常完美。焊接电路板。先测试两个 AS1117 稳压芯片的并联情况。通过可编程直流电源和电子负载对其进行测试。

▲ 图1.2.1 测试电路图

▲ 图1.2.2 测试PCB图

三、测试结果

下面使用电子负载，分别测试两个 AS1117 的输出特性。负载电流范围是 300mA。两个1117  的输入电压为9V。记录每个电流下对应的芯片输出。这是第一个芯片的输出特性。右面电压下降快，猜测是芯片发热造成的。第二个芯片特性比较平直。估计它的温度特性比较稳定。从这里可以看到 ，两个稳压芯片输出特性差别还是蛮大的。

▲ 图1.3.1 AS1117芯片1的电压与电流特性

cdim=[0.0000,0.0030,0.0061,0.0091,0.0121,0.0152,0.0182,0.0212,0.0242,0.0273,0.0303,0.0333,0.0364,0.0394,0.0424,0.0455,0.0485,0.0515,0.0545,0.0576,0.0606,0.0636,0.0667,0.0697,0.0727,0.0758,0.0788,0.0818,0.0848,0.0879,0.0909,0.0939,0.0970,0.1000,0.1030,0.1061,0.1091,0.1121,0.1152,0.1182,0.1212,0.1242,0.1273,0.1303,0.1333,0.1364,0.1394,0.1424,0.1455,0.1485,0.1515,0.1545,0.1576,0.1606,0.1636,0.1667,0.1697,0.1727,0.1758,0.1788,0.1818,0.1848,0.1879,0.1909,0.1939,0.1970,0.2000,0.2030,0.2061,0.2091,0.2121,0.2152,0.2182,0.2212,0.2242,0.2273,0.2303,0.2333,0.2364,0.2394,0.2424,0.2455,0.2485,0.2515,0.2545,0.2576,0.2606,0.2636,0.2667,0.2697,0.2727,0.2758,0.2788,0.2818,0.2848,0.2879,0.2909,0.2939,0.2970,0.3000]
vdim=[3.2967,3.2967,3.2967,3.2967,3.2934,3.2925,3.2917,3.2909,3.2902,3.2895,3.2887,3.2881,3.2870,3.2863,3.2855,3.2848,3.2841,3.2833,3.2826,3.2817,3.2809,3.2801,3.2794,3.2787,3.2780,3.2773,3.2766,3.2756,3.2748,3.2741,3.2734,3.2727,3.2720,3.2713,3.2705,3.2698,3.2691,3.2682,3.2675,3.2668,3.2661,3.2654,3.2646,3.2640,3.2633,3.2625,3.2616,3.2609,3.2601,3.2594,3.2588,3.2580,3.2573,3.2566,3.2557,3.2550,3.2543,3.2536,3.2529,3.2522,3.2514,3.2507,3.2500,3.2493,3.2486,3.2477,3.2470,3.2463,3.2456,3.2450,3.2442,3.2434,3.2428,3.2418,3.2412,3.2404,3.2396,3.2389,3.2382,3.2375,3.2367,3.2357,3.2350,3.2342,3.2334,3.2328,3.2321,3.2314,3.2307,3.2295,3.2287,3.2279,3.2270,3.2262,3.2253,3.2245,3.2236,3.2225,3.2214,3.2205]

#!/usr/local/bin/python
# -*- coding: gbk -*-
#******************************
# TEST1.PY                   - by Dr. ZhuoQing 2023-12-21
#
# Note:
#******************************

from headm import *
from tsmodule.tsvisa        import *

dl3021open(109)


dl3021setcurrent(0)
dl3021on()

cdim = linspace(0, 0.3, 100)
vdim = []


for c in cdim:
    dl3021setcurrent(c)
    time.sleep(1)
    v = dl3021volt()
    printff(c, v)
    vdim.append(v)
    tspsave('u1', cdim=cdim, vdim=vdim)


dl3021setcurrent(0)
dl3021off()

plt.plot(cdim, vdim, lw=3)

plt.xlabel("Current(A)")
plt.ylabel("Voltage(VA)")
plt.grid(True)
plt.tight_layout()
plt.show()


#------------------------------------------------------------
printf("a")



#------------------------------------------------------------
#        END OF FILE : TEST1.PY
#******************************

▲ 图1.3.2 第二个芯片对应的输出电流与电压

cdim=[0.0000,0.0030,0.0061,0.0091,0.0121,0.0152,0.0182,0.0212,0.0242,0.0273,0.0303,0.0333,0.0364,0.0394,0.0424,0.0455,0.0485,0.0515,0.0545,0.0576,0.0606,0.0636,0.0667,0.0697,0.0727,0.0758,0.0788,0.0818,0.0848,0.0879,0.0909,0.0939,0.0970,0.1000,0.1030,0.1061,0.1091,0.1121,0.1152,0.1182,0.1212,0.1242,0.1273,0.1303,0.1333,0.1364,0.1394,0.1424,0.1455,0.1485,0.1515,0.1545,0.1576,0.1606,0.1636,0.1667,0.1697,0.1727,0.1758,0.1788,0.1818,0.1848,0.1879,0.1909,0.1939,0.1970,0.2000,0.2030,0.2061,0.2091,0.2121,0.2152,0.2182,0.2212,0.2242,0.2273,0.2303,0.2333,0.2364,0.2394,0.2424,0.2455,0.2485,0.2515,0.2545,0.2576,0.2606,0.2636,0.2667,0.2697,0.2727,0.2758,0.2788,0.2818,0.2848,0.2879,0.2909,0.2939,0.2970,0.3000]
vdim=[3.3192,3.3187,3.3188,3.3182,3.3152,3.3149,3.3142,3.3134,3.3128,3.3121,3.3115,3.3109,3.3100,3.3093,3.3088,3.3081,3.3075,3.3068,3.3061,3.3052,3.3046,3.3039,3.3032,3.3026,3.3020,3.3013,3.3006,3.2997,3.2990,3.2984,3.2977,3.2970,3.2964,3.2957,3.2950,3.2944,3.2937,3.2927,3.2920,3.2913,3.2907,3.2900,3.2893,3.2885,3.2879,3.2872,3.2862,3.2855,3.2848,3.2840,3.2832,3.2824,3.2817,3.2808,3.2798,3.2789,3.2781,3.2774,3.2767,3.2759,3.2748,3.2738,3.2730,3.2722,3.2713,3.2702,3.2693,3.2686,3.2677,3.2665,3.2655,3.2649,3.2640,3.2626,3.2613,3.2600,3.2589,3.2579,3.2565,3.2551,3.2539,3.2519,3.2504,3.2488,3.2472,3.2457,3.2442,3.2424,3.2406,3.2385,3.2365,3.2336,3.2306,3.2280,3.2247,3.2216,3.2181,3.2136,3.2086,3.2029]

▲ 图1.3.3 将两个稳压芯片电流电压曲线绘制在一起

#!/usr/local/bin/python
# -*- coding: gbk -*-
#******************************
# TEST2.PY                   - by Dr. ZhuoQing 2023-12-21
#
# Note:
#******************************

from headm import *

cdim0, vdim0 = tspload('u1', 'cdim', 'vdim')
cdim1, vdim1 = tspload('u2', 'cdim', 'vdim')

plt.plot(cdim0, vdim0, lw=3, label='U1')
plt.plot(cdim1, vdim1, lw=3, label='U2')

plt.xlabel("Current(A)")
plt.ylabel("Voltage(V)")
plt.grid(True)
plt.legend(loc="upper right")
plt.tight_layout()
plt.show()


#------------------------------------------------------------
#        END OF FILE : TEST2.PY
#******************************

在测试过程中，不小心短路将第二芯片烧坏了。更换了一支新的芯片。重新测量它的输出特性。对比三个1117 的输出特性，可以看到它们之间的差别还是比较大的。

▲ 图1.3.4 第三只1117 的电压电流特性

cdim=[0.0000,0.0030,0.0061,0.0091,0.0121,0.0152,0.0182,0.0212,0.0242,0.0273,0.0303,0.0333,0.0364,0.0394,0.0424,0.0455,0.0485,0.0515,0.0545,0.0576,0.0606,0.0636,0.0667,0.0697,0.0727,0.0758,0.0788,0.0818,0.0848,0.0879,0.0909,0.0939,0.0970,0.1000,0.1030,0.1061,0.1091,0.1121,0.1152,0.1182,0.1212,0.1242,0.1273,0.1303,0.1333,0.1364,0.1394,0.1424,0.1455,0.1485,0.1515,0.1545,0.1576,0.1606,0.1636,0.1667,0.1697,0.1727,0.1758,0.1788,0.1818,0.1848,0.1879,0.1909,0.1939,0.1970,0.2000,0.2030,0.2061,0.2091,0.2121,0.2152,0.2182,0.2212,0.2242,0.2273,0.2303,0.2333,0.2364,0.2394,0.2424,0.2455,0.2485,0.2515,0.2545,0.2576,0.2606,0.2636,0.2667,0.2697,0.2727,0.2758,0.2788,0.2818,0.2848,0.2879,0.2909,0.2939,0.2970,0.3000]
vdim=[3.3015,3.3014,3.3012,3.3008,3.2982,3.2976,3.2969,3.2963,3.2957,3.2951,3.2945,3.2938,3.2930,3.2924,3.2918,3.2913,3.2907,3.2901,3.2896,3.2887,3.2881,3.2876,3.2870,3.2865,3.2859,3.2853,3.2847,3.2839,3.2833,3.2828,3.2822,3.2817,3.2811,3.2806,3.2799,3.2794,3.2789,3.2781,3.2775,3.2769,3.2763,3.2757,3.2752,3.2746,3.2740,3.2735,3.2726,3.2720,3.2714,3.2709,3.2702,3.2696,3.2691,3.2684,3.2675,3.2669,3.2663,3.2657,3.2651,3.2644,3.2635,3.2629,3.2622,3.2616,3.2609,3.2600,3.2593,3.2586,3.2580,3.2572,3.2565,3.2558,3.2550,3.2539,3.2531,3.2524,3.2516,3.2508,3.2500,3.2492,3.2484,3.2473,3.2465,3.2457,3.2449,3.2441,3.2434,3.2425,3.2417,3.2406,3.2398,3.2389,3.2382,3.2372,3.2363,3.2353,3.2342,3.2329,3.2317,3.2304]

▲ 图1.3.5 三个芯片输出特性

  将两个1117并联在一起，输入电压同样为9V，此时可以看到，它们各自的静态电流不太一样。一个为 0.9mA，另外一个为 5.6mA。下面使用电子负载测量两个 1117 并联后各自的电流变化。

使用电子负载测试并联后的两个 1117 工作电流。工作电流可以通过DH1766 直接读出。测量结果令人感到惊讶。居然在整个输出电流范围内，两个 1117 只有一个为负载提供电流。另外一个始终输出 0mA。这让我破防了。实在是没有想到。手触碰两个 1117，会发现一个已经发烫，另外一个没有温度。

▲ 图1.3.6 并联后两个1117在不同负载下输出电流

#!/usr/local/bin/python
# -*- coding: gbk -*-
#******************************
# TEST3.PY                   - by Dr. ZhuoQing 2023-12-21
#
# Note:
#******************************

from headm import *


from tsmodule.tsvisa        import *

dl3021open(109)
dl3021setcurrent(0)
dl3021on()


#------------------------------------------------------------

cdim = linspace(0, 0.3, 100)
c1dim = []
c2dim = []


for c in cdim:
    dl3021setcurrent(c)
    time.sleep(1)
    ca = dh1766call1()

    printff(c, ca)
    c1dim.append(ca[0])
    c2dim.append(ca[1])

    tspsave('1117', cdim=cdim, c1dim=c1dim, c2dim=c2dim)


dl3021setcurrent(0)
dl3021off()

plt.plot(cdim, c1dim, lw=3, label='U1')
plt.plot(cdim, c2dim, lw=3, label='U2')

plt.xlabel("Current(A)")
plt.ylabel("Current(A)")
plt.grid(True)
plt.tight_layout()
plt.show()


#------------------------------------------------------------
#        END OF FILE : TEST3.PY
#******************************

cdim=[0.0000,0.0030,0.0061,0.0091,0.0121,0.0152,0.0182,0.0212,0.0242,0.0273,0.0303,0.0333,0.0364,0.0394,0.0424,0.0455,0.0485,0.0515,0.0545,0.0576,0.0606,0.0636,0.0667,0.0697,0.0727,0.0758,0.0788,0.0818,0.0848,0.0879,0.0909,0.0939,0.0970,0.1000,0.1030,0.1061,0.1091,0.1121,0.1152,0.1182,0.1212,0.1242,0.1273,0.1303,0.1333,0.1364,0.1394,0.1424,0.1455,0.1485,0.1515,0.1545,0.1576,0.1606,0.1636,0.1667,0.1697,0.1727,0.1758,0.1788,0.1818,0.1848,0.1879,0.1909,0.1939,0.1970,0.2000,0.2030,0.2061,0.2091,0.2121,0.2152,0.2182,0.2212,0.2242,0.2273,0.2303,0.2333,0.2364,0.2394,0.2424,0.2455,0.2485,0.2515,0.2545,0.2576,0.2606,0.2636,0.2667,0.2697,0.2727,0.2758,0.2788,0.2818,0.2848,0.2879,0.2909,0.2939,0.2970,0.3000]
c1dim=[0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009,0.0009]
c2dim=[0.0056,0.0056,0.0056,0.0124,0.0162,0.0192,0.0222,0.0250,0.0277,0.0307,0.0338,0.0366,0.0405,0.0434,0.0463,0.0491,0.0519,0.0549,0.0579,0.0617,0.0647,0.0674,0.0705,0.0733,0.0763,0.0792,0.0822,0.0861,0.0891,0.0921,0.0950,0.0979,0.1009,0.1038,0.1066,0.1094,0.1123,0.1163,0.1192,0.1219,0.1250,0.1278,0.1308,0.1337,0.1367,0.1396,0.1434,0.1461,0.1491,0.1520,0.1549,0.1579,0.1607,0.1636,0.1676,0.1704,0.1733,0.1763,0.1792,0.1820,0.1858,0.1888,0.1917,0.1945,0.1974,0.2014,0.2043,0.2072,0.2100,0.2129,0.2158,0.2186,0.2216,0.2255,0.2284,0.2313,0.2343,0.2372,0.2401,0.2430,0.2458,0.2498,0.2527,0.2556,0.2583,0.2614,0.2642,0.2671,0.2700,0.2738,0.2769,0.2798,0.2827,0.2854,0.2886,0.2913,0.2941,0.2980,0.3009,0.3038]

更换了另外一对1117重新进行测量。使用电子负载为并联1117 提供负载。它们输出电流相差 50% 左右。

▲ 图1.3.7 另外两组1117 并联输出电流

  最后测试两个 7805 并联的结果。输入电压为 9V。负载电流从0变化到300mA，可以看到两个7805 的工作电流相差很大。

▲ 图1.3.8 两个 7805 并联输出

※ 总  结 ※

本文对于两个稳压芯片的并联进行了测试，可以看到这种情况如果不使用均流方法，是无法工作的。与其并联这些稳压芯片，不如采用其它方式进行扩容。