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 )
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