New design experiments are very quick, easy and save electronics components when you have a breadboard for testing your circuitry. Power supplies are necessary for powering the circuitry. Most of the time, the amount of current required remains low but often we need to have two different voltage such as 5V and 12V or +/- 12V.
This project describes how to build a double ELEGOO Breadboard (830 Points) with a dual adjustable power supply with display. The overall Bill of Material remains below 32€ (w/o transfo) and use the new low cost MTTQ modules that come with a display to provide the dual ⎓1.5-30V/ 0.3A variable power supplies.
Notes about the transformer:
The characteristics of the power supplier will mainly depend of the type of transformer. A 2x 12V~ (30VA) will enable a 2x 15V~ / 1A power supply. DO NOT EXCEED 24V~ to stay below 36V ⎓ , the maximum voltage allows on the MTTQ module input.
Step 1: The XL4105 MTTQ Module
The MTTQ module exposes 4 adjustments:
- the Minimum Input level is not used (must be set to 100% - turn until an output voltage becomes available and continue until max)
- The LED threshold defines the current threshold where the LEDs switches. We will use this adjustment to set our Overload indicator. We kept only the red LED as overload indicator.
- The Constant Current adjustment defines the maximum output current. To adjust it, connect a 10A multimeter to short circuit the output and turn the potentiometer until reading the desire value.
- The Output Voltage adjustment will be remove and replaced by a 10-turn 50K potentiometer to offer a smoother control of the output voltage.
The MTTQ module ensures protections against:
- Short circuit by limiting the maximum output current.
- Over heating by switching off the module.
For our dual power supply we also need additional protections against :
- Polarity inversion if a reversed voltage source is connected.
- Current injection if the circuit under test provide voltage higher than the output voltage
There is already a provision on the MTTQ module for the Current injection protection by replacing the JP1 strap by a 1N4001 diode (see photo).
For the Polarity inversion, a 1N4001 diode connected in parallel on the outputs will do it.
The MTTQ module has a double display for reading :
- Output / Input voltages
- Current / Power
We do not need the Input voltage and Power reading because the first will never change and the second is almost useless.
The multimeter accuracy is given to +/- 0.1V but the current accuracy is very poor due to the low levels we are dealing with.
Step 2: Building the Hardware
To build our breadboard, we use a 2x 24V~ (12VA) transformer. It delivers 34V⎓ peak voltage matching the MTTQ module input specifications.
For filtering the output the residual switching oscillations, a LC (190µH/100µF-50V) circuit is added. Extra components such as rectifier bridges, capacitors and coils are located on an additional board. Take care of the output negative wiring because there is a resistor in serie for measuring the current. Therefore negative lines between input and output cannot be shared.
The current design provides two independent power supplies that can be used for providing two separated voltages or placed in series for providing +/- voltages.
The LEDs (the red for overload) and 50k/10-turn Voltage potentiometers will be located on the top cover.
The MTTQ module adjustment must be set as described above. We have set the current limitation to 300 mA whereas the Overload LED was adjusted to start lighting at 250mA as a pre-warning.
Step 3: Bill of Material
The bill of material without the transformer:
BangGood MPPT XL4105 Step down 6,16 € 2 12,32 € Amazon 2W10M 1000V 2A Rectifier bridge 0,09 € 2 0,19 € Amazon TC5026 190µH 0,28 € 2 0,56 € Amazon Runrain 50 K Ohm 3590s-2-503L 1,93 € 2 3,86 € Amazon 470µF / 50V 0,47 € 4 1,88 € Amazon 47 µF / 63V 0,22 € 4 0,86 € Amazon Fuse Holder 0,37 € 1 0,37 € Amazon Power switch 0,51 € 1 0,51 € Amazon PCB XINTE 10Stk. 5x7cm 0,45 € 1 0,45 € Amazon Buttons 0,50 € 2 1,00 € Amazon 5mm LED holder 0,12 € 2 0,24 € Amazon 4mm Banane plug female 0,15 € 4 0,60 € Transfo 220V / 2x24V 12W 1 - € Amazon Cable holder 0,05 € 1 0,05 € 3P+G 1M50 cable 1,50 € 1 1,50 € Amazon ELEGOO Breadboard 830 Points 3,33 € 2 6,66 € Spacers, screws, etc. 0,20 € 1 0,20 € -------- Grand Total 31,26 €