Bi-polar power supply from ready made Chinese dc-dc step down LM2596 modules
They claim to have quite high parameters and the cost of the module is less than the price of the parts that go into it. I was tempted by the small size of the board. I decided to buy a few and try them out. I hope my experience will be useful for radio amateurs who are not too experienced.
Contents
Kamrad, consider the datagore recommendations
Useful and tested gizmos, good to go.
Tested in the editorial lab or by readers.
I bought the LM2596 modules as pictured above on Aliexpress. Although on the website it showed 50V solid state capacitors, the capacitors are common, and half of the modules have 16V capacitors.
↑ It is hard to call this a stabilizer.
You would think that just take a transformer, diode bridge, connect the module to them, and we have a stabilizer with output voltage of 3…30V and current up to 2A (briefly up to 3A).
I did so. Without a load it was fine. The transformer with two windings of 18 V and the promised current up to 1.5 A (the wire was obviously thin to the eye, it turned out that way). I needed a +-18V regulator and I set it to the right voltage.
With a 12 ohm load, the current is 1.5 A, here’s the oscillogram, 5 V/cell vertical.
It’s hard to call this a stabilizer.
The reason is simple and straightforward: the capacitor on the board is 200 uF, it serves only for normal operation of the DC-DC converter. When applying voltage to the input from a laboratory power supply, everything was fine. The way out is obvious: you need to power the AVR from a source with low ripple, i.e. add a capacitor after the bridge.
↑ Fighting against ripple
↑ Increased input capacitance
With the 4700 uF capacitor on the input side, the ripple at the output was greatly reduced, but at 1.5A it was still noticeable. With the output voltage reduced to 16 V, a perfect straight line (2 V/cell).
The voltage drop on the DC-DC module should be at least 2…2.5V.
Now you can watch the ripple at the output of the pulse converter.
You can see small ripples with a frequency of 100 Hz, modulated with a frequency of a few tens of kHz.
↑ LC filter on the output
The LM2596 datasheet recommends an additional LC filter at the output. So we did. I used a cylindrical core from a broken computer power supply and wound the core in two layers with 0.8mm wire.
The red color on the board shows the place to install a jumper – the common wire of the two channels, and the arrow – the place to solder the common wire, if you do not use terminals.
Let’s see what has become of the HF pulsations.
They are gone. There is still a little ripple with a frequency of 100 Hz. Not ideal, but not bad.
Just to note, when output voltage goes up, the choke in the module starts to rattle and HF noise starts to grow sharply, but once the voltage goes down (with 12 Ohm load), all noise and interference disappears.
↑ Final wiring diagram of the LM2596 modules
Under continuous 1A load the components get noticeably hotter: the diode bridge, the IC, the module choke, and most of all the choke (additional chokes are cold). Heating to the touch is 50 degrees.
When working from the laboratory power supply, the heating at currents of 1.5 and 2 A is tolerable for a few minutes. For long term work with higher currents a bigger choke and a heat sink on the chip are desirable.
↑ Mounting
This ensured convenient mounting and cooling of the modules. The racks can be heated a lot when soldering, they will not shift, unlike simple pins. The same design is convenient if you need to solder external wires to the board – good rigidity and contact. The board allows easy replacement of the DC-DC module if needed.
General view of the board with the chokes from the halves of some ferrite core (inductance is not critical).
Despite the tiny size of the DC-DC module, the overall dimensions of the board are comparable with the board of an analog regulator.
↑ Conclusion.
1. If you need a transformer with a high current or extra voltage secondary, in this case the load current may be higher than the transformer winding current.
2. For currents on the order of 2 A or more a small heat sink on the diode bridge and the 2596 chip is desirable.
3. A large capacitor is desirable, this has a favorable effect on the operation of the regulator. Even a large and high quality capacitor heats up a bit, hence a small ESR is desirable.
4. To suppress ripple with frequency conversion, an LC filter on the output is necessary.
5. This regulator has a distinct advantage over the usual compensation regulator in that it can operate in a wide range of output voltages, at low voltages you can get more current at the output than the transformer can provide.
6. Modules allow you to make a power supply with good parameters simply and quickly, avoiding the pitfalls of making boards for switching devices, that is good for novice radio amateurs.
Power Supplies – Power and Not-so-Powerful for MCCBs
The circuit is relatively simple and is a two-pole stabilized power supply. The arms of the power supply are mirrored so that the circuit is perfectly symmetrical.
Power Supply Specifications: Nominal input voltage: ~18. 22V Maximum input voltage: ~28V (limited by capacitor voltage) Maximum input voltage (theoretical): ~70V (limited by the maximum voltage of the output transistors) Output voltage range (at ~20V input): 12. 16V Rated output current (at 15V output voltage): 200mA Maximum output current (at 15V output voltage): 300mA Supply voltage ripple (at rated output current and 15V voltage): 1.8mA Supply voltage ripple (at maximum output current and 15V voltage): 3.3mA
This power supply can be used to power preamplifiers. The PSU provides fairly low ripple at a fairly high (for preamplifiers) current.
As an analog of MPSA42/92 you can use KSP42/92 or 2N5551/5401 transistors. Do not forget to check the pinout. Transistors BD139/BD140 can be replaced by BD135/136 or other transistors with similar parameters.
Transistors VT1 and VT6 must be mounted on the heat sink, the place for which is provided on the PCB.
As VD2 and VD3 you can use any 12V voltage regulators.
Small power supply with unipolar to bipolar conversion.
Very often a hobbyist has a transformer, but with only one winding and it is necessary to have bi-polar voltage at the output. Exactly for this purpose the following circuit can be used:
The circuit is characterized by its simplicity and versatility. A wide range of AC voltages can be applied to the circuit input, limited only by the allowable voltage of the bridge diodes, the allowable supply capacitor voltage, and the KE voltage of the transistors. The output voltage of each arm will be equal to half of the total supply voltage or (Uin*1,41)/2, for example: with an input AC voltage of 20V, the output voltage of one arm will be (20*1,41)/2=14V.
As transistors VT1 and VT2 you can use ANY complementary transistors, just remember about the pin assignment. Good choices are MPSA42/92, KSP42/92, BC546/556, KT3102/3107 and so on. Also consider when replacing transistors with analogs their maximum allowable QE voltage, it should not be less than the output voltage of the arm.
Powerful bipolar power supply with half-bridge rectification.
In my practice I like to use transformers with 4 identical secondary windings for powering the UHF, particularly the TA196 transformer, TA163 and similar. When using these transformers it is convenient to use a double half-bridge half-bridge rectifier circuit instead of a bridge one. The circuit of the power supply itself is shown below:
Not only TA, TAN, TPP, TN transformers can be used for this circuit, but also any other transformers with 4 identical voltage windings.
The pin numbering corresponds to the pin numbering of the TA196 and similar transformers.
Powerful power supply with half-bridge rectification, with additional low power buses.
Based on a TA196 transformer or other transformers with 4 secondary windings you can arrange the following circuit:
The +/-40V voltage (or other, depending on the voltage of your transformer windings) is used to power the power amplifier. The +/-15V bus can be used to power the preamp and input buffer. The +12V bus can be used for auxiliary needs, such as powering a fan, protection, or other non-demanding devices.
You can use any other 12V regulator instead of 1N4742 or 3.3V regulator instead of 1N4728.
You can use any other pair of complementary transistors of average power for 1-2A current instead of BD139/140 transistors. Transistors VT1, VT2 and VT3 must be mounted on a heat sink.
The pin numbering corresponds to the pin numbering of the TA196 and similar transformers.
Pictures of some of the power supplies shown.
All power supplies come with 100% working printed circuit boards.
