Doug S
Flashlight Enthusiast
Another CPF member sent me a few ARC 1AAA converter boards for testing. You know who you are; Thanks!
I tested several of these boards and found their performance to be reasonably consistant among them. The boards were tested with a single 5mm LED as a load and a 1.1 ohm sense resistor was added in series for monitoring output current. For testing purposes an input capacitor was added to the circuit. This prevents the long lead length from the power supply from interferring with the proper operation of the circuit. In the data which follows the Vout is measured across both the sense resistor and the LED so the efficiency values should be about the same as if the sense resistor were absent. The following data is for the sample which had both the highest output currents and efficiency. I noted that among the samples I received, the value of the output capacitor ranged from 2uF to 47uF. This should have negligible effect on electrical I/O efficiency but the higher values should yield better electrical to light conversion efficiency.
THE DATA
<font class="small">Code:</font><hr /><pre>
Vin(V) Iin(mA) Vout(V) Iout(mA) Eff(%)
0.203 15.55 2.78 .64 56.5
0.503 42.7 3.02 4.3 60.6
0.803 76.8 3.22 12.0 62.7
0.898 90.2 3.27 15.7 63.3
0.998 101.7 3.32 19.6 64.2
1.102 118.4 3.37 25.0 64.6
1.202 168.7 3.47 36.4 62.3
1.280 198.0 3.47 39.1 53.5
1.393 180.0 3.49 41.6 57.9
1.500 172.4 3.51 44.6 60.6
2.00 145.2 3.59 57.9 71.5
3.00 158.6 3.79 106.5 84.9
</pre><hr />
Operating frequency at Vin=1.0V ranged from 128 to 144kHz among samples and varied slightly with Vin. Even though the circuit continues to operate down to 0.2V it requires about 0.72V to startup. Note that Iin starts dropping for Vin>1.3V. This is due to the relatively low switch current limit of the IC used, about 280mA.
Here are the details of this circuit. The switching device is a 3 terminal stepup voltage regulator with a fixed output voltage of 5V in a SOT23-5 package. Normally this type of switching regulator IC requires only 3 external components: an inductor, a schottky diode, and output filter capacitor. The inductor value is 22uH and the output cap either 2 or 47uF. Because the LED load prevents the output from ever reaching 5V, the device runs wide open with output determined by Vin, inductor value, and load characteristics. This is exactly the same design approach used in the Dorcy 1AAA circuit, the only difference being the particular choice of IC. Note that unless the capacitor is removed, this circuit is not damaged by operating without load.
The characteristics of this circuit immediately suggest one worthwhile mod. This would be to mod an ARC 1AA using a 1W luxeon and a 3V CR type AA cell. This likely would power the luxeon with around 150-200mA depending on Vf and provide very long runtime, 6hrs+.
For comparison, here is roughly equivalent test data for the Dorcy 1AAA circuit.
<font class="small">Code:</font><hr /><pre>
Vin Iout[mA] Eff[%]
.50 4.3 66.5
.70 8.4 66.8
.90 15.2 69.4
1.1 23.4 70.6
1.2 34.4 72.4
1.3 53.0 70.5
1.5 95.6 67.7
LED Vf ranged from 3.089V at 4.3mA to 3.816 at 95.6mA.
</pre><hr />
Note that this Dorcy 1AAA data did not include the voltage across a 1 ohm sense resistor in the efficiency calculation so it slightly [1-2%] understates the efficiency relative to the method used for the ARC circuit at higher currents.
Note that the output current of the ARC varies less with Vin than that of the Dorcy. This is due to the action of the onboard current limit of the ARC IC coming into play at Vin>1.3V. In the 1AAA configuration this is of limited consequence since only a small [<10%] portion of the battery discharge will be at 1.3V and above at these input current levels. The lower efficiency of the ARC relative to the Dorcy is almost entirely due to the higher IC switch resistance which is about 3 ohms for the ARC circuit vs 1 ohm for the Dorcy.
I tested several of these boards and found their performance to be reasonably consistant among them. The boards were tested with a single 5mm LED as a load and a 1.1 ohm sense resistor was added in series for monitoring output current. For testing purposes an input capacitor was added to the circuit. This prevents the long lead length from the power supply from interferring with the proper operation of the circuit. In the data which follows the Vout is measured across both the sense resistor and the LED so the efficiency values should be about the same as if the sense resistor were absent. The following data is for the sample which had both the highest output currents and efficiency. I noted that among the samples I received, the value of the output capacitor ranged from 2uF to 47uF. This should have negligible effect on electrical I/O efficiency but the higher values should yield better electrical to light conversion efficiency.
THE DATA
<font class="small">Code:</font><hr /><pre>
Vin(V) Iin(mA) Vout(V) Iout(mA) Eff(%)
0.203 15.55 2.78 .64 56.5
0.503 42.7 3.02 4.3 60.6
0.803 76.8 3.22 12.0 62.7
0.898 90.2 3.27 15.7 63.3
0.998 101.7 3.32 19.6 64.2
1.102 118.4 3.37 25.0 64.6
1.202 168.7 3.47 36.4 62.3
1.280 198.0 3.47 39.1 53.5
1.393 180.0 3.49 41.6 57.9
1.500 172.4 3.51 44.6 60.6
2.00 145.2 3.59 57.9 71.5
3.00 158.6 3.79 106.5 84.9
</pre><hr />
Operating frequency at Vin=1.0V ranged from 128 to 144kHz among samples and varied slightly with Vin. Even though the circuit continues to operate down to 0.2V it requires about 0.72V to startup. Note that Iin starts dropping for Vin>1.3V. This is due to the relatively low switch current limit of the IC used, about 280mA.
Here are the details of this circuit. The switching device is a 3 terminal stepup voltage regulator with a fixed output voltage of 5V in a SOT23-5 package. Normally this type of switching regulator IC requires only 3 external components: an inductor, a schottky diode, and output filter capacitor. The inductor value is 22uH and the output cap either 2 or 47uF. Because the LED load prevents the output from ever reaching 5V, the device runs wide open with output determined by Vin, inductor value, and load characteristics. This is exactly the same design approach used in the Dorcy 1AAA circuit, the only difference being the particular choice of IC. Note that unless the capacitor is removed, this circuit is not damaged by operating without load.
The characteristics of this circuit immediately suggest one worthwhile mod. This would be to mod an ARC 1AA using a 1W luxeon and a 3V CR type AA cell. This likely would power the luxeon with around 150-200mA depending on Vf and provide very long runtime, 6hrs+.
For comparison, here is roughly equivalent test data for the Dorcy 1AAA circuit.
<font class="small">Code:</font><hr /><pre>
Vin Iout[mA] Eff[%]
.50 4.3 66.5
.70 8.4 66.8
.90 15.2 69.4
1.1 23.4 70.6
1.2 34.4 72.4
1.3 53.0 70.5
1.5 95.6 67.7
LED Vf ranged from 3.089V at 4.3mA to 3.816 at 95.6mA.
</pre><hr />
Note that this Dorcy 1AAA data did not include the voltage across a 1 ohm sense resistor in the efficiency calculation so it slightly [1-2%] understates the efficiency relative to the method used for the ARC circuit at higher currents.
Note that the output current of the ARC varies less with Vin than that of the Dorcy. This is due to the action of the onboard current limit of the ARC IC coming into play at Vin>1.3V. In the 1AAA configuration this is of limited consequence since only a small [<10%] portion of the battery discharge will be at 1.3V and above at these input current levels. The lower efficiency of the ARC relative to the Dorcy is almost entirely due to the higher IC switch resistance which is about 3 ohms for the ARC circuit vs 1 ohm for the Dorcy.
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