DIY AD9833 signal generator – dual 5V power supply (part 4)

Today’s continuation of the DIY signal generator based on an AD9833 is going to be about a dual rail 5V power supply. In the first part I have introduced you to a variable gain amplifier stage. The power supply is going to be used to power the mentioned operational amplifier.

Links to project’s all posts

  1. VCA822 Gain Amplifier Circuit
  2. LM7171 Offset Circuit
  3. Gain and Offset Control Filter Circuit
  4. Dual 5V Power Supply (this post)
  5. Dual 12V TPS65131 Power Supply
  6. Battery Charging Circuit with BQ24295
  7. Basic WEB Interface
  8. IPS Capacitive LCD on an ESP32
  9. IPS LCD, ESP32 with eSPI library and Touch screen
  10. Final PCB Design for the DIY Waveform Generator
  11. Custom Design PCBs and How To Get Them Manufactured
  12. Soldering the PCB
  13. AD9833 Library and Further Output Noise Reduction
  14. Arduino BQ24295 Battery Charger Library
  15. LCD GUI with LVGL on ESP-32
  16. 3D Printed Enclosure
  17. Finished DIY generator

The Device

So, the signal generator is going to be a battery powered device. This means, that power IC must work with 3 to 4.5 V input voltage. It also has to deliver at least 50 mA of current on both rails. Finally, output voltages need to be around +5V and -5V.

With those requirements ON Semiconductor’s LV52117QA chip was chosen. It is designed to deliver dual 5V with up to 100mA output current. It is also quite cheap solution: the IC itself costs around 2 USD and it requires only bare minimum component count. The only and main problem with this chip is that it is very tiny. Which, on one hand, is good as it takes not much space on a PCB, but, on the other hand, it is very difficult to solder at home…

After deciding on which IC to use, I have made a schematic for a test PCB:

LV52117QA schematic dual 5V output

As you can see it is the same schematic as shown in the chips datasheet. There is actually not a lot to talk about, maybe one thing I could note – LV52117QA has integrated synchronous circuit, so there is no need to have additional MosFets on board, which further minimizes whole circuit. Also, instead of suggested by the datasheet 50 kOhms (R2) resistor, 51k was used (as I didn’t have 50k at hand).

LV52117QA dual converter hand soldered
Tiny IC in the middle of the PCB… Hand soldered with a hot air gun for SMD components 🙂

This PCB was made by me at home. I have written a tutorial how it can be done either by etching with chemicals (used in this case) or with a CNC router.

Board measurements

Converters PCB's test circuit V2
Test and measurement circuit

So, I have tested the board with dual 100 Ohm load and dual 47 Ohm load, and got such input/output values:

With 100 Ohm load:

  • Output voltage U1 = + 4.84 V
  • Output voltage U2 = – 4.97 V
  • Battery current I = 146.7 mA
  • Battery voltage U = 3.72 V

With 47 Ohm load:

  • Output voltage U1 = + 4.8 V
  • Output voltage U2 = – 4.94 V
  • Battery current I = 347 mA
  • Battery voltage U = 3.508 V
LV52117QA Dual Power Converter Board Full
Test circuit

From these values, converters efficiency can be calculated – it is around 88 % at 100 Ohm and 83 % at 47 Ohm load. Which is actually not bad at all. Note, that this efficiency will depend on inductor resistance, in this case these 4.7 uH inductors were used. As they are a bit overkill for this converter in the future I will use something smaller in size.

Also, as I have used 51k resistor instead of recommended 50k, positive output voltage was a bit lower than it should have.

So, this circuit will supply variable gain amplifier stage with a VCA822 and in another part I should talk about dual 12V power supply for the offset control stage.

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