Marconi showed that sparks could produce a great deal of
RF with their radio transmitter experiments. This can be
death to the XL4005 output FETs.) I learned this after
blowing two modules. Two diodes have been added to
help prevent this problem.
To set your current limiting: 1) Shut off the power
supply; 2) Place a short across the red to black output
terminals; 3) Turn on your power supply; 4) Set the current
limit; 5) Turn off the power supply; and 6) Remove the
short. Your power supply is now ready to use. Set the
desired output voltage and the current will automatically
limit at the value set in step 4 discussed above.
Using the voltage adjust knob, you should be able to
set the voltage between .8V and 30V. To set the current
limit, follow the procedure in the paragraph above.
Why Use a CV/CI
Have you ever blown up a breadboard or electronic
project when you turned on the power supply? If you
haven’t, you will. Burning resistors give off a very distinctive
smell. Plastic transistors, ICs, and electrolytic capacitors can
literally explode. So, how do you prevent this catastrophic
event? We start by estimating the current your masterpiece
will draw. Then, we multiply that value by 1.5 to 2, and set
the constant current to that value. Next, set the output
voltage. Now, you may connect the circuit under test to
your CV/CI power supply and turn it on. If the power
supply immediately goes into current limit, you may have a
wire hooked up wrong or the electrolytic capacitor in
Double-check your wiring, power supply connections,
and electrolytic capacitors. If all that checks out okay, it
could be your circuit’s current estimate was too low.
The next step requires safety glasses. I know this from
experience as it took about a month for the welt on my
forehead to heal when an electrolytic capacitor (wired in
backwards) blew up. Now, turn the power supply on and
with a maximum current in mind (maybe x4), SLOWLY turn
up the current limit and watch for the power supply voltage
to stabilize to your preset value or to have smoke appear
(whichever comes first).
Battery Charging —
Using a CV/CI
A constant voltage/constant current power supply can
be used as a battery charger for rechargeable batteries.
Overcharging or overheating batteries can be very
dangerous and cause them to explode. A CV/CI power
supply can charge with a preset maximum constant current
until it approaches the preset constant voltage setting, at
May 2014 31
; FIGURE 12.
tape to make
; FIGURE 11.
HP 0957-2093 AC Power Adapter; ~$10
5A Constant Current/Voltage Module with Voltmeter and
Ammeter (USA seller nyplatform, includes a heatsink);
LM2596S DC-DC Buck Converter Module 32V input,
Adjustable Output Voltage; <$2
2x 10K ohm Multi-Turn Wire Wound Potentiometers
Project Enclosure ( 5" x 2"), Model 270-1803 Radio
7805 - 5V Regulator; <$1
2x 1N4007 Brushless DC Fan 5V 0.12A; <$4
Red and Black Binding Posts; ~$1
Red/Blue/Orange LEDs; $3 100 pcs
LED Holder/Chrome Metal; <$2 10 pcs
2x Knobs (Plastic); <$5.50 5 pcs
Lockable 5. 5 mm x 2.1 mm DC Power Plug plus Socket;
1) All products were purchased from eBay unless
otherwise listed. Check out your usual favorite suppliers
instead where possible.
2) eBay prices typically include shipping.