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Googling around, we discovered the TPS305, a seemingly nice hobby-lab power supply from the Chinese brand WANPTEK, unknown to us. We ordered a test sample from Banggood and you can read the results of our tests in this article. |
Introduction to the TPS305 from WANPTEK
Manufacturer, price and suppliers
WANPTEK appears to be a brand name of the Chinese company ‘Shenzhen Guce Electronic Technology Co., Ltd.’ This company was founded in Shenzhen in 2017 and specialises with producing electronic power supplies. The TPS305 is the cheapest model in the TPS range and delivers 0 V to 31 V at a current of 0 A to 5.2 A. The device is, at the time of writing this article, available via Banggood for € 48.89. This is very cheap, as on AliExpress the numerous vendors are pricing this power supply at around € 70.
The TPS305 hobby-lab power supply
The power supply delivers an output voltage of 00.00 V to 31.00 V with an adjustable output current between 0.000 A and 5.200 A. You can set the voltage with a resolution of 10 mV and the current with a resolution of 1 mA. As the picture below shows, the TPS305 is very compact. The metal housing has a front panel measuring 14.5 cm by 8.0 cm and the depth is 21.0 cm. The power supply weighs just 1.2 kg.
The TPS305 is available in white and in dark grey. The power supply has just one rotary knob that allows you to set both voltage and current. Around that one rotary knob are four push buttons:
- OUT:
Standby switch, apply the voltage to the outputs after pressing this button. - V/A:
Selects whether to use the rotary knob to set the voltage or current. - OCP:
Activates the built-in electronic fuse. - ON/OFF:
The power switch.
Under the control panel are three 4 mm output sockets. The voltage is offered between the red and black, the green is connected to the metal housing and to the mains plug earth.
On the left, you can see the large display showing voltage, current and power. Interestingly, the seven-segment indicators are white. If you activate the power supply via the ‘OUT’, indications appear next to the figures:
- C.V:
Operation as a constant voltage source. - C.C:
Operation as constant current source. - OCP:
The electronic fuse is activated. - OUT:
Voltage is applied to the outputs.
To the left of the numerical displays are a USB-A and a USB-C connector. Through these connectors, you can charge 5 V devices. According to the manual, the TPS305 supports various fast-charging protocols, such as Qualcomm QC2.0, QC3.0, APPLE, Huawei FCP and SCP Samsung AFC, up to a maximum power of 18 W.
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| The look of the TPS305. (© Banggood) |
The front and rear panel
In the image below, we have joined the front and rear panel in one photo. On the back of the enclosure you will find a standard C14 Euro chassis socket with built-in fuse (5 mm x 20 mm). A hefty air outlet grille for the built-in fan takes up about half of the rear panel. This fan makes quite a bit of noise, but does not run continuously. It is controlled via a temperature sensor that monitors the temperature of the large heatsink on the PCB.
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| Front and rear panel of the TPS305. (© 2024 Jos Verstraten) |
The scope of delivery
In addition to the power supply, the package contains:
- A high-quality earthed mains cable.
- A thick two-wire connection cable for the output voltage.
- A professional seven-language manual of 60 pages.
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| The extras included. (© 2024 Jos Verstraten) |
The manual
As already written, it is excellently done. We have scanned the English-language part and posted it on our account at ‘archive.org’:
The specifications of the TPS305
According to the manufacturer, this power supply meets the following specs:
- Mains voltage: 115 V ~ 230 V switchable
- Constant output voltage: 0.00 V ~ 31.00 V
- Resolution output voltage: 10 mV
- Constant output current: 0.000 A ~ 5.200 A
- Resolution output current: 1 mA
- Voltage setting accuracy: better than 0.5 % ± 3 mV
- Output stability voltage: better than 0.2 % ± 3 mV
- Ripple voltage: better than 20 mVrms
- Setting accuracy current: better than 0.5 % ± 3mA
- Output stability current: better than 0.2 % ± 3 mA
- Ripple current: less than 5 mArms
- Recovery time: less than 500 μs
- Temperature coefficient: smaller than +100 ppm/℃
- OCP (Over Current Protection): activatable
- Auxiliary functions: USB-A and USB-C fast chargers
- Dimensions: 145 mm x 80 mm x 210 mm
- Weight: 1.2 kg
The electronics in the TPS305
Removing ten bolts
The metal housing consists of a low U-shaped lower part to which a higher U-shaped upper part is screwed. After removing ten bolts, you can remove that upper part and the interior of the TPS305 emerges.
The electronics in the TPS305
The electronics are housed on two PCBs. One fills most of the enclosure. The second is screwed against the front panel and contains the electronics for controlling the display and the two USB connectors. We like what we see very much. The PCB's soldering, wiring and final assembly look professional. The green 4 mm output socket on the front panel goes via a thick wire to a solder tab under one of the four metal spacers used to screw the PCB into the housing. The ground lug of the mains power connector is connected to the enclosure in an identical manner.
The soldered connections carrying the mains voltage are fitted with shrink tubing. The mains switch, top right in the picture below, is of excellent quality.
The position of the fan in relation to the heatsink of the MOSFET that controls the output voltage via pulse-width modulation is optimal. That MOSFET is soldered onto the PCB and the heatsink is afterwards screwed on top of this component.
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| The interior of the TPS305. (© 2024 Jos Verstraten) |
The mains voltage is rectified and smoothed by two 220 μF - 200 V electrolytics connected in series. The primary circuit of the switched-mode power supply is controlled by a DK124 from ‘Shenzhen DongXinke Microelectronics Chip’. This eight-pin chip takes care of converting the rectified mains voltage into a high-frequency pulse voltage that controls the primary of the transformer ZM2023/12/01. Of course, feedback is provided from the secondary side via an optical coupler that provides galvanic isolation between primary and secondary.
On the main PCB we find a TL494C from Texas Instruments. It is not clear whether this ‘Pulse-Width-Modulation Control Circuit’ chip is in the main circuit or has something to do with powering the two USB ports.
On the display PCB is a TM1629C from ‘Shenzhen Titan Micro Electronics Co., Ltd.’. This chip is responsible for controlling the display.
Operating the TPS305 power supply
Switching on the device
After switching on the device, the power supply always enters the standby mode, i.e. without voltage on the output sockets. You can see this quite clearly by the indication ‘OFF’ on the power display. Of course, the other two displays show the voltage and current settings that are stored in memory.
Setting voltage and current
Press the ‘V/A’ key to switch between setting the voltage or current. You can identify which setting is active by one of the seven-segment displays flashing. By pressing the round button, you can select one of the four displays of voltage or current. By turning that knob, you can vary the value. The two set values of voltage and current are kept in memory.
Activating the outputs
Press the ‘OUT’ key. Next to the power display, the green text ‘OUT’ lights up and the voltage appears on the output sockets. Next to the voltage display, the green text ‘C.V’ appears. This means that the power supply is now in constant voltage mode.
If the power supply should supply more current than set, this green indicator extinguishes and the red indicator ‘C.C’ lights up. The device is now operating in constant current mode and delivering the programmed current to the load.
The electronic fuse function ‘OCP’
When you press this button, the red text ‘OCP’, acronym of ‘Over Current Protection’, appears next to the power display. The electronic fuse is now enabled. If the power supply should now supply more current than the set value, the electronic fuse switch off the output voltage, the text ‘OCP’ appears in the power display and a buzzer beeps. You can reset the power supply by briefly pressing the ‘OUT’ button.
Enabling and disabling the beeps on operation
In factory mode, the built-in buzzer beeps with every operation with the controls. If this annoys you, you can turn these beeps off by pressing the rotary switch for a few seconds. You will hear a very last beep and from then on you can operate the TPS305 without the device making any noise.
Testing WANPTEK's TPS305
The ground resistance
We measured the resistance between the green 4 mm banana plug socket on the front panel and the ground lug on the mains plug:
- 0.298 Ω with our ET3255 from East Tester
- 0.3183 Ω with our 8842A from Fluke
Of course, we measure such a small resistance using the four-wire kelvin method.
Voltage setting accuracy
We connected our multimeter 8842A from Fluke to the outputs and set the power supply to various output voltages. The table below shows the real values of the unloaded output voltage. With our Philips broadband millivoltmeter PM2454B, we also measured the unloaded noise and ripple voltage on the output at the various settings.
Both values are excellent. Even at a setting of 100 mV, the TPS305 delivers a very accurate output voltage.
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| The accuracy of the voltage setting. (© 2024 Jos Verstraten) |
The unloaded output noise and ripple
The oscillogram below shows the unloaded output noise and ripple when set to 30.00 V.
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| Unloaded output noise and ripple at 30.00 V. (© 2024 Jos Verstraten) |
Accuracy of current setting
We short-circuit the outputs of the power supply with our multimeter ET3255 from East Tester switched to 12 Adc and set the output current to various values. The measurement is performed at an output voltage of 5.00 V. The results are summarised in the table below. Only at the lowest settings of 10 mA and 50 mA does the power supply deliver an all but accurate output current, the other values are excellent! Just to be sure, we measure that lowest setting again with the Fluke 8842A, which measures 14.981 mA. So the deviation is in the TPS305 and not in our meters.
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| The accuracy of the current setting. (© 2024 Jos Verstraten) |
Output stability at 5.00 V output voltage
Output stability defines the constancy of the output voltage as a function of the load current. This quantity is not necessarily the same at every output voltage, so it must be tested at various voltages. Of course, the current is set to the maximum value of 5.2 A. We start at 5.00 V, the results are shown in the table below. The power supply is connected to an adjustable load type EBD-A20H. On the output are, obviously, the 8842A, the PM2454B and our oscilloscope XDS2102A from OWON.
The voltage difference between zero and full load is only 22.1 mV. Using ohm's law, you can then immediately calculate the internal resistance of the power supply. Indeed, a voltage drop of 22.1 mV at a current variation of 5 A yields 4.42 mΩ.
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| The output stability at 5.00 V output voltage (© 2024 Jos Verstraten) |
The ripple at 5.00 V and 5.000 A
Output stability at 12.00 V output voltage
Input stability at 30.00 V and 4.000 A
Efficiency η
Long-term stability at 10.00 V and 5.000 A
Thermal stability
Impact of load variation on output voltage
Functioning of the 'OCP'
The previous table shows that the ripple suddenly rises sharply when you load the power supply with almost the maximum current. The 20 mVrms from the specifications is then greatly exceeded. In the two oscillograms below, you can see what this ripple looks like. What is noticeable is that the ripple is very quiet. The narrow irregular spikes, which we have seen in several other cheap switched-mode power supplies, are completely absent here. The time magnification on the right shows that the signal is almost sinusoidal and therefore there are few harmonics in it. What you see here is probably the result of the filtered pulse width modulated signal used to generate the output voltage.
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| The ripple at 5.00 V and 5.000 A. (© 2024 Jos Verstraten) |
Output stability at 12.00 V output voltage
We repeat the above measurements, but now with the output voltage set to 12.00 V.
The results are again summarised in the table below. The voltage drops by 22 mV, which corresponds to an internal resistance of 4.4 mΩ. The shape of the ripple is similar to this at 5.00 V.
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| The output stability at 12.00 V output voltage. (© 2024 Jos Verstraten) |
Output stability at 29.00 V output voltage
Why at 29.00 V and not at 30.00 V? Because our adjustable load EBD-A20H protests with ‘input voltage too high’ at 30.00 V, but diligently gets to work with one volt less. The voltage drop is 24 mV, good for an internal resistance of 4.8 mΩ. Even at this output voltage, the ripple resembles this one at 5.00 V.
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| The output stability at 29.00 V output voltage. (© 2024 Jos Verstraten) |
Input stability at 30.00 V and 4.000 A
This parameter defines the constancy of the output voltage when the input voltage of the power supply varies. So our variac is taken off and the output voltage is measured when the mains voltage is varied between 200 V and 250 V. The results are again summarised in a table.
This shows that the input stability is excellent. When the mains voltage is varied by 50 V, the output voltage goes up by only 196 mV!
There is something to note about the variation on the ripple voltage. Although the TPS305 appears to be excellent at keeping the output voltage almost constant at an unrealistic supply of only 200 Vac, the electronics have problems with the ripple. This is high at this supply voltage. As a second observation, it appears that dropping the current from 5.000 A to 4.000 A has a big impact on the ripple. A previous test showed that the ripple voltage is 29.1 mV at 29.00 V and 5.000 A. Reducing the current to 4.000 A reduces the ripple to 6.50 mV.
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| The input stability of the TPS305. (© 2024 Jos Verstraten) |
Efficiency η
Efficiency gives the percentage ratio between the power you get out of a device and the power you put into it. Our variac has an ammeter, so we can use the input stability test to measure the efficiency of the TPS305.
At an input voltage of 231 V, the power supply draws a current of 0.6 A, so the input power is 138.6 W. At this voltage, the power supply delivers a voltage of 30.051 V at 4.00 A load current. The output power is 120.2 W.
The efficiency:
η = 120.2 W / 138.6 W
η = 86,7 %
Long-term stability at 10.00 V and 5.000 A
In this test, the power supply cooled to room temperature is subjected to a maximum load of 5.0 A at 10.00 V output voltage and it is measured how stable the output voltage remains as a function of time. This heavy load causes the power supply to heat up internally and the question is how well the electronics are designed to compensate for the output voltage drift due to this heating. The results are again summarised in the table below. As can be seen from these data, the maximum voltage drift is only +13.3 mV and the output voltage remains stable after only about 30 minutes.
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| The long-term stability of the TPS305. (© 2024 Jos Verstraten) |
Thermal stability
About the thermal behaviour of this power supply, after the long-term test, we are not worried. Even after delivering 10 A for half an hour, only a lukewarm air came out of the back and the metal case did not feel really warmed up.
The functioning of the 'OUT' function
If you use the 'OUT' pushbutton to apply the voltage to the output sockets, this voltage should appear neatly on the power supply output without any transition phenomena. If you press 'OUT' again, the voltage should return to 0 V just as neatly. We test this at a voltage of 8.00 V and a load current of 1 A. The results are summarised in the combined oscillogram below. The power supply behaves nicely!
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| Switching the output voltage on and off via the ‘OUT’ button. (© 2024 Jos Verstraten) |
Behaviour in the event of a short circuit
We set the power supply to a voltage of 12.0 V and a maximum current of 5.0 A. Afterwards, we loaded the output with 1 A and briefly shorted it with a mercury switch from an old thermostat. You can see the behaviour of the output voltage on the oscillogram below. There is no sign of overshoots, oscillations or other undesirable phenomena. Again, the TPS305 behaves perfectly!
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| The behaviour in the event of a short circuit. (© 2024 Jos Verstraten) |
Impact of load variation on output voltage
When you power a circuit, it draws a certain current. If this current suddenly increases or decreases, the output voltage of the power supply must remain constant and not show any strange transient phenomena. We test this by setting the TPS305 to 12.0 V and 5.0 A and powering a 1.0 A load. Afterwards, we suddenly briefly switch an additional load in parallel, so that the load current increases to 4.5 A. You can see the reaction of the output voltage of the TPS305 in the oscilllogram below. Of course, the ripple increases, but there is no sign of any unwanted transient phenomena. Again, excellent behaviour from this power supply!
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| Response to sudden current increase. (© 2024 Jos Verstraten) |
Functioning of the 'OCP'
This function in itself works well, the TPS305 switches to standby if you draw more current than set. However, we noticed that when there was a short circuit, there were some pretty hefty sparks at the contacts. So we tested the short-circuit current by setting the power supply to maximum current and maximum voltage. Afterwards, we shorted the power supply over a 1 Ω wire-wound resistor that had an exact value of 1.317 Ω.
The oscillogram below shows the peak voltage generated across this resistor.
The sensitivity of the oscilloscope is 5 V/div and the peak is 3.4 divisions high. A voltage of 17.0 V is therefore generated across the 1.317 Ω resistor. This corresponds, according to ohm's law, to a short-circuit current of no less than 12.9 A! Apparently, the ‘OCP’ function discharges a hefty electrolytic capacitor across the output terminals.
So you should rather not use that ‘OCP’ function, because the flow of such currents is not good for anything, not for your load and certainly not for the electronics in the power supply.
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| The short-circuit current with the ‘OCP’ function. (© 2024 Jos Verstraten) |
Our conclusion on WANPTEK's TPS305
Testing this device yielded the pleasant surprise that this TPS305 is a very good performing power supply for the money you have to pay for it. We can think of very few criticisms. Obviously, professional electronics engineers will turn their noses up at a power supply that delivers an rms ripple of around 30 mV at full load. But don't forget that that ripple drops to 6.5 mV if you reduce the current from full load (5.0 A) to 4.0 A. We think that, for a power supply costing less than fifty euros, is an excellent value.
Also, the fact that in all our tests no overshoots, spikes or oscillations of any kind occurred on the output voltage argues in favour of the designers of this power supply. We have tested several power supplies in the same price range where this was anything but the case.
For every hobbyist who plans to purchase a universal lab power supply, we think the TPS305 is an excellent choice
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TPS305 powr supply 31 V ~ 5.2 A
TPS305 powr supply 31 V ~ 5.2 A