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The 2-transistor Black regulator

App a02; +5v output, good all round


Specs

  • 87% efficiency (from 70mA to 300mA out)
  • Excellent powerband, (from 20mA to 600mA)
  • Very cheap circuit
  • Decent 5v regulation
  • Input: 10v to 18v
  • Output: 5v @ 600mA maximum





    The Circuit

    
    +15v -------*-----------------*--------,
                |                 |        |  Q1
                |        470 ohm  R1       |  PNP
                |                 |        E  BC327
          8k2   RZ                *------B
                |                 |        C
                |                 |        |          (measured:)
                |            2k7  R2       |   470uH  (460uH, 0.7 dc ohms)
                |                 |        |
                |      NPN BC337  |        *----L1-------*------ +5v out
                |                 C  Q2    |             |
                *----*----*-----B          |             |
                |    |    |       E--------|-------------*
                |    |    |                |             |
                |    |    |                |             |
                |    |    '------C2--------*             |
         zener  |    |           2nF       |             | 47uF
          ZD1   -    |                     -             C 16v
         5.6v   ^    C1                    ^ D1  1A      |
        400mW   |    |                     | schottky    |
                |    | 6.8nF               | 1N5819      |
                |    |                     |             |
    Gnd --------*----*---------------------*-------------*------ Gnd
    
    (these are the actual parts values as used in the test, as
    well as a 100uF cap on the power input)
    

    Chart





    Test Data
       V in   I in     P in     V out    I out    P out    Freq    I gain    Eff (%)
       15v      1.5mA  0.0225w   4.96v     0.3mA  0.0015w    dc!     0.20      6.6%
       15       3.7    0.0555    5.00       5     0.0250     155     1.35     45.0
       15       5.5    0.0825    4.97      10     0.0497     137     1.82     60.2
       15       7.3    0.1095    4.95      15     0.0743     116     2.05     67.8
       15       9.1    0.1365    4.95      20     0.0990     97      2.20     72.5
       15      10.9    0.1635    4.94      25     0.1235     86      2.29     75.5
       15      12.5    0.1875    4.93      30     0.1479     78      2.40     78.9
       15      15.9    0.2385    4.91      40     0.1964     66      2.52     82.3
       15      19.5    0.2925    4.90      50     0.2450     57      2.56     83.8
       15      22.9    0.3435    4.89      60     0.2934     50      2.62     85.4
       15      26.2    0.3930    4.88      70     0.3416     45      2.67     86.9
       15      30.0    0.4500    4.87      80     0.3896     41      2.67     86.6
       15      33.3    0.4995    4.87      90     0.4383     37      2.70     87.7
       15      37.0    0.5550    4.86      100    0.4860     34      2.70     87.6
       15      44.1    0.6615    4.85      120    0.5820     31      2.72     88.0
       15      51.1    0.7665    4.85      140    0.6790     31      2.74     88.6
       15      58.4    0.8760    4.84      160    0.7744     31      2.74     88.4
       15      65.6    0.9840    4.84      180    0.8712     31      2.74     88.5
       15      74.2    1.1130    4.84      200    0.9680     30      2.70     87.0
       15      92.6    1.3890    4.83      250    1.2075     30      2.70     86.9
       15      112.0   1.6800    4.83      300    1.4490     30      2.68     86.3
       15      131.6   1.9740    4.82      350    1.6870     30      2.66     85.5
       15      150.6   2.2590    4.81      400    1.9240     30      2.66     85.2
       15      172.5   2.5875    4.81      450    2.1645     30      2.61     83.7
       15      193.9   2.9085    4.80      500    2.4000     30      2.58     82.5
       15      235.0   3.5250    4.80      600    2.8800     30      2.55     81.7
       15      280.0   4.2000    4.80      700    3.3600     31      2.50     80.0
       15      330.0   4.9500    4.80      800    3.8400     37      2.42     77.6
    

    Notes

    Inductor is 10mm diameter x 12mm high, 470uH at 0.7 dc ohms. This is a good compromise of enough inductance but quite low DC ohms.

    If you change RZ to about 4k7 or 5k6, load voltage regulation gets approx 2x to 3x better, at the cost of about 2% efficiency. This may be a good change if you need currents over 150mA and efficiency is not super critical.

    If your load device only needs a specific current range, you can tune the circuit to give 91% efficiency in a range about 80ma to 150mA. This is done by increasing RZ to about 10k or 12k, fiddling with the values of C1 and C2 to tune the circuit to a specific high efficiency band.

    It will give higher efficiency with a better inductor, I had a 560uH 0.15 ohm inductor here that got 92% efficiency over a good range just by plugging into this circuit.


    Parts List

    Transistor	Q1	TO92		BC327		10c
    Transistor	Q2	TO92		BC337		7c
    
    Inductor	L1	0.7ohm		470uH		50c
    Schottky Diode	D1	1A		1N5819		20c
    
    Zener Diode	Z1	400mW		5.6v		6c
    
    Capacitor	C1	polyester	2nF		5c
    Capacitor	C2	polyester	6.8nF		5c
    Capacitor	CL	16v electro	47uF		6c
    Capacitor	CS	25v electro	47uF		6c
    
    Resistor	RZ	1/4w		8k2		2c
    Resistor	R1	1/4w		470 ohms	2c
    Resistor	R2	1/4w		2k7		2c
    TOTAL						    $1.21 AUD
    				 (in US dollars:    $0.67 USD )
    

    - end -

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