LM317-based Wide-Range Adjustable Voltage Power Supply KitThese ECROS Technology adjustable-voltage power supply kits use the Fairchild Semiconductor LM317MT or LM317T voltage regulators. These regulators have the following features:
No Longer Available For PurchaseECROS Technology has closed down and as a result Mini- and Flexi-PSUs are no longer available for purchase. These pages are maintained for the benefit of existing owners. |
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Mini-PSU Parts Kit contents:
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Additional Parts in Flexi-PSU Kit:
† The regulator must be inserted as U1, not U2. ‡ Because of the modest current rating of the slide switch supplied for SW1, it is recommended that an external switch, with a higher rating, be used if it will be frequently operated while a high load current is flowing. |
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Technical Specifications
Output Voltage Range - For lower output voltage ranges, install as R1 the 1 kohm, 100mW trimmer potentiometer supplied in the kit. To obtain the range you want, select R2 from those supplied as follows:
- 270 ohms - 1.25 to 5.9 volts (IR2 = 4.6mA, PR1 = 22mW)
- 220 ohms - 1.25 to 6.9 volts (IR2 = 5.7mA, PR1 = 32mW)
- 180 ohms - 1.25 to 8.2 volts (IR2 = 6.9mA, PR1 = 48mW)
- 150 ohms - 1.25 to 9.6 volts (IR2 = 8.3mA, PR1 = 69mW)
To obtain higher output voltages, do not reduce R2 further or the power rating of R1 will be exceeded. Use the supplied 2 kohm trimmer instead.
- 270 ohms - 1.25 to 10.5 volts (IR2 = 4.6mA, PR1 = 43mW)
- 220 ohms - 1.25 to 12.6 volts (IR2 = 5.7mA, PR1 = 65mW)
- 180 ohms - 1.25 to 15.1 volts (IR2 = 6.9mA, PR1 = 96mW)
- 150 ohms - 1.25 to 17.9 volts (IR2 = 8.3mA, PR1 = 139mW)
If you are ordering assembly and test please be sure to specify your selection of R1 and R2 from the above choices. Unused parts will be sent along with your assembled PSU.
Input Voltage - For the regulator to operate properly, the input voltage to the PSU must always be the output voltage plus the regulator dropout voltage plus the voltage drop across D1, if used. For example, with the output set at 5V and D1 bridged with a wire link, the input voltage must be at least 8V (5 + 3). This includes supply ripple. Continuing the example, if, at full load, ripple causes the input voltage to drop 0.5V below its average value during each half-cycle, then the average input voltage should be 8.5V.
Power Dissipation - Heat dissipated in the regulator, in watts, will be the product of the load current in amps and the voltage dropped across the regulator. Again, using the above example, suppose you apply an input voltage of 12V. The regulator will drop 7V (12 - 5). At 0.5 amps, the heat dissipated will be 3.5W (7 x 0.5). With the compact heatsinks supplied in the 0.5A kits, ECROS Technology recommends that you limit power dissipation in the regulator to 4W. This is based on personal safety concerns. At higher power, the circuit will continue to function but the heatsink will become very hot. If you touch it, you may not pull away fast enough to avoid some lasting discomfort. The 1.5A kit with the Flexi-PSU PCB has a large heatsink and power dissipation is not a concern.
(Use the menu on the left hand side to go back to the Mini-PSU introduction.)