I. Introduction

If the output current of one voltage stabilizing chip cannot meet the requirements, can two voltage stabilizing chips be simply connected in parallel to provide a larger output current? Let’s do a simple test to see what problems may arise.

2. Test circuit

Design a parallel circuit of two voltage regulator chips. Two independent voltage regulator chips 7805 are given here. Their outputs can be connected in parallel to provide output current to the load. The inputs are separated and the operating current is provided by different DC power supplies, which also indirectly obtains the operating current of each voltage regulator. A 1117, 3.3V voltage regulator chip is also designed below. This circuit board can also test the 1117 voltage regulator chip. Make the test circuit using a single panel.

Get the test board after a minute. Check out the production. very perfect. Solder the circuit board. First test the parallel connection of two AS1117 voltage regulator chips. Test it with programmable DC power supply and electronic load.

▲ Figure 1.2.1 Test circuit diagram

▲ 图1.2.2 测试PCB图

3. Test results

Next, electronic loads are used to test the output characteristics of the two AS1117s. The load current range is 300mA. The input voltage of two 1117s is 9V. Record the corresponding chip output at each current. This is the output characteristic of the first chip. The voltage on the right side drops quickly, which is probably caused by the chip heating. The characteristics of the second chip are relatively flat. It is estimated that its temperature characteristics are relatively stable. It can be seen from here that the output characteristics of the two voltage regulator chips are quite different.

▲ 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
#******************************

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]

#!/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
#******************************

During the test, a short circuit accidentally burned out the second chip. Replaced with a new chip. Remeasure its output characteristics. Comparing the output characteristics of the three 1117s, we can see that the difference between them is quite large.

▲ 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]

Two 1117s are connected in parallel, and the input voltage is also 9V. At this time, you can see that their respective quiescent currents are different. One is 0.9mA and the other is 5.6mA. Next, an electronic load is used to measure the current changes of two 1117s connected in parallel.

Use an electronic load to test the operating current of two 1117s connected in parallel. The operating current can be read directly through DH1766. The measurements were surprising. Surprisingly, within the entire output current range, only one of the two 1117s provides current to the load. The other one always outputs 0mA. This broke my guard. I really didn't expect it. If you touch two 1117s with your hands, you will find that one is hot and the other has no temperature.

#!/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]

Another pair of 1117 was replaced and measured again. Use an electronic load to provide load for the parallel 1117. Their output currents differ by about 50%.

▲ 图1.3.7 另外两组1117 并联输出电流

Finally, test the results of two 7805s connected in parallel. The input voltage is 9V. The load current changes from 0 to 300mA. It can be seen that the operating currents of the two 7805s are very different.

▲ 图1.3.8 两个 7805 并联输出

※ Summarize ※

This article tested the parallel connection of two voltage regulator chips. It can be seen that this situation will not work if the current sharing method is not used. Rather than connecting these voltage regulator chips in parallel, it is better to use other methods to expand the capacity.