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Benchtop PSU 3xDPS3005

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Kalvin:
Hi,

I have started designing a very simple, switched mode, benchtop PSU with three separate outputs, based on DPS3005 adjustable power modules. The mains transformer is 120VA with four separate secondary windings: 24VAC@1.3A, 16VAC@2.2A, 16VAC@2.2A and 9VAC@1.1A. The 9VAC winding will be used for any logic needed for relay operation etc. The 9VAC winding might also be used in later state to power a Raspberry Pi Zero W.

Here are the main specs:

- Three separate outputs with 2x12V@2A and 1x20V@1A output which can be connected in series or parallel
- Each output can be enabled/disabled individually (DPS3005 has enable/disable button)
- All the outputs can be enabled/disabled simultaneously by a switch (three relays with SPDT contacts disconnecting the load from the PSU)
- Each output can be programmed to CV or CC mode with voltage and current limit (built-in to DPS3005 by default)
- Each output will provide voltage, current and power display (built-in to DPS3005 by default)

The diode at the output is actually a transient suppressor diode (TVZ) which will clamp any high voltage spikes at the output from inductive loads. The noise suppression is done using simple PI-filters at the DPS3005s inputs and outputs (If I have understood correctly, the DSP3005 will generate some switching noise from its inputs, thus the filtering also at the inputs).

Unfortunately the DPS3005 modules I have at the moment do not contain the serial port control ability, which would have been a very nice addition to the power supply capability. With the serial port control capability one could add a Raspberry Zero W inside the box which would control all three modules and provide some long term measurement statistics etc. any any other scripting ability with WIFI connectivity The three channels and the Raspberry Pi could be isolated very easily with simple opto couplers.

Any comments or suggestions are welcome!

Br,
Kalvin

Kalvin:
One idea that has been lingering in my mind is to use INA226 for each output and a simple MCU to measure the output voltage/current/power for logging purposes. This would require three cheap DC/DC-converter providing a 5V power supply for the INA226 and MCU for each channel. Also, two opto couplers per channel are required to provide an isolated communication channel between the INA226/MCU and the three Uart-to-USB adapter boards connected to the Raspebrry Pi Zero.

StillTrying:
"use INA226 for each output "

How would you keep all the INA226's within their -0.3 to +36V common mode range, especially if the DPS3005s have a mosfet switch in their GND before the sense resistor.

Kalvin:

--- Quote from: StillTrying on May 02, 2018, 10:51:27 am ---"use INA226 for each output "

How would you keep all the INA226's within their -0.3 to +36V common mode range, especially if the DPS3005s have a mosfet switch in their GND before the sense resistor.

--- End quote ---

Yes, I am aware that the DPS3005 has a low-side current sense and a low-side MOSFET which will enable/disable the output.

As INA226 and the respective MCU will be powered from an isolated DC/DC module, I will connect the INA226 across the output diode (which will be a TVZ in the final design) and connect the 0V of the MCU/INA226 to the negative output (cathode side of the output diode), the INA226 should not see any excessive voltages. Also, each channel will be floating relative to each other due to the isolated DC/DC modules and opto-isolated serial connections, there shouldn't be any problems.

Edit: Added the updated diagram to include the INA226s.
Edit2: Moved the diode/TVZ to the output side of the INA226 blocks where they belong.

StillTrying:
I didn't know you were adding sense resistor, from there you could connect to the 226's 3005's own GND current sense resistor.
I think you'd have to provide some protection to Vbus from the reverse -1V or more when the protection diode conducts. Vbus's input impedance is 800k, so easy enough to protect.

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