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Variable Regulated Power Supply

Price : INR 370.00

The Variable Regulated Power Supply can provide variable output is adjustable from 1.6 volts to about 30 volts using ic LM317. This kit is based on the LM317 type integrated circuit. This is a simple, but low-ripple power supply, and an excellent project if you're starting out in electronics. It will suit your needs for most of your bench testing and prototype applications. The output is adjustable from 1.5 volts to about 30 volts. Maximum current is about 1.5 amps which is also sufficient for most of your tinkering. It is easy to build and can be pretty cheap if you have some or all the required parts.

Circuit description :
The 220VAC coming from the power-cord is fed to the transformer TR. The 24VAC output (approximately) from the transformer is presented to the bridge rectifier diode D1 TO D4, and here rectified from AC (Alternating Current) to DC (Direct Current). The LM317's max input voltage is 36V. so right at the maximum edge. Better to obtain a transformer with a little less voltage and be safe. A 0-18VAC transformer will still give you about 26VDC and more than anyone hobbyist ever need. The amperage of the transformer should be 1.5A or so. That way it does not get hot. The pulsating DC output from bridge is filtered via the C1 capacitor  and fed to 'IN'-put of the adjustable LM317 regulator (IC1).The output of this regulator is your adjustable voltage of 1.5 to 30 volts varied via the 'Adj' pin and the 5K pot VR1. The large value of C1 makes for a good, low ripple output voltage.

D5 is a general purpose 1N4001 diode, used as a feedback blocker. It steers any current that might be coming from the device under power around the regulator to prevent the regulator from being damaged. Such reverse currents (spikes) usually occur when devices are powered down. The 'ON' Led will be lit via the 1.8K (1800 ohm) resistor R1. The  current through the led will be between 12 - 20mA @ 2V depending on the type and color Led you are using. You may need to modify the value of R1 depending on your type LED. C2 is a 0.1uF (100nF) decouple capacitor to filter out the transient noise which can be inducted into the supply by stray magnetic fields. Under normal conditions this capacitor is only  required if the regulator is far away from the filter cap, but I added it anyway. C3 improves transient response. This means that while the regulator may perform perfectly at DC and at low frequencies, (regulating the voltage regardless of the load current), at higher frequencies it may be less effective. Adding this 1 uF capacitor should improve the response at those frequencies.

Construction :
First of all you should place on the board the resistors the capacitors , the diodes & make sure that the electrolytic capacitors & diodes are connected the right way round because they are polarized. Make a careful visual inspection for mistakes, shorts across adjacent tracks etc. and if everything seems to be all right. In our kit the secondary connection of the transformer are connected.

If all is well, and you are finished assembling and soldering everything, check all connections. Check capacitors C1 & C3 for proper polarity (especially for C1, polarity reversal may cause explosion). Hookup a multi-meter to the power supply output jacks.

Set the multi-meter for DC volts. Switch on (led will light, no smoke or sparks?) and watch the meter movement. Adjust potentiometer P1 until it reads on your multi-meter 15Volts. Adjust Pot until the panel meter (if so installed) also reads 15volts. The panel voltmeter is optional. When done, note any discrepancies between your multi-meter and the power supply meter at full scale (max output). Maybe there is none, maybe there is little, maybe there is a lot because of your choice of transformer but you will be aware of it. Just make sure your multi meter reading and panel meter read as close as possible.

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