This project represents what I believe to be a effective tool for electronici, a medium power Bench supply capable of controlling voltage and current and having some fixed outputs for 5V and 3.3V (no current limiting). This for eas of use.
The FlexiPower Bench is the based on the µSupply (EEVBlog) and the FlexiPower (ROBERTO LO GIACCO, on circuitmaker). Unlike both designs mine isn't operatable form a battery, that is not without some extra circuitry. It is designed to be used with SMPS's from 12-24V delivering a minimum of 1A (3A prefered).
This wide operation voltage is possible thanks to a sepic boost converter. this converter is used to limit the heat production in the rest of the circuit and to be able to get 24V out of a 12V power pack. I tried to find a good balance between bom cost, eficiency and amount of components. This while still offering the most basic and usefull capabilities:
- Single (Current limited) Channel
- Max theoretical output voltage: 30V
- Max output voltage (my design): 20V (limited by reference)
- Max Current: 1A (limited by LT3080)
- Fine and Course curent measurement:
- 10uA resolution for current up to 40mA
- 20uA resolution for current up to 80mA
- 40uA resolution for current up to 160mA
- 80uA resolution for current up to 320mA
- 2mA resolution for current up to 1A
- current limiting resolution of XmA (unknown at the moment, depents on PWM)
- Remote control (Not known how yet!)
- reverse voltage protection
- dedicated current sensing connector
Dave Jones, author of the core power supply design, has gone through an extensive description of all the critical choices, the design evolutions over time and all the details in a series of YouTube videos: I will try to briefly summarize here only the key parts and my additions.
I've designed FlexiPower as to provide two completely independent supply channels, which I've modularized into their own schematic, and most of the following considerations will apply to each one of those separately.
The original power supply is battery powered by a two cells Li Ion or Li Poly battery: this provides a maximum voltage of 8.4V when full charged. To achieve lower voltages the battery output is fed into a high current, very stable, linear voltage regulator, the LT3080, capable to deliver up to 1.1A. My design isn't equiped for this and uses a 12-24 Power pack of meanwell supply. Nevertheles this design can be used as a battery powered PSU, this thanks to the sepic converter. This means that an aditional charger sircuit is needed.
To achieve the higher voltages desired at the supply output, the input voltage is fed into a sepic converter circuit. This sepic converter is designed to give a variable output voltage between 5V and 24V. The output of this device can be controlled via a potentiometer (I2C digital pot in our case) and enabled at will, that implies the controller logic will enable the booster circuit only when necessary. This reduces considerably the amount of power wasted and thermal dissipation is substantially simplified: the entire power supply can be fanless.
To provide the right output voltage it's not enough to be able to do so: measuring the produced voltage is key to perform the necessary variation to adjust the process accordingly to the desired result. To do this a precision voltage reference of 2.048V or 3.300V and a simple voltage divider along with the 10 bit ADC built into the micro controller to determine the output voltage with a 20mV precision. At the same time we fed the same voltage reference into a 10 bit DAC which output is then multiplied by a factor of 10 by an OpAmp to get a 20mV resolution in controlling the output desired on the LT3080.
Current measuring is similarly performed via different paths, depending on the output level, but in both cases it's based on a 1 Ohm shunt resistor network made by ten 10 Ohm 1% 0.5W resistors in parallel: this results in a voltage drop of 1mV per mA and a maximum power capacity way above the required 1W with a precision statistically better than the 1% of each component resistor.
In case of currents lower than 320mA, the INA219 integrated circuit is used to obtain a very precise reading with a resolution varying from 10uA (yes, micro amps!) for very low currents (up to 40mA) to 80uA.
When the supplied current goes above the capacity of the INA219 the shunt resistor voltage drop is measured using the micro controller built in 10 bit ADC but an OpAmp is used to remove any disturbance in the readings.
At the same time current limiting is performed in a very simple way: a PWM is output from the micro controller into a smoothing circuit and the filtered output is then fed into the inverting input of an OpAmp in a comparator configuration. At the same time the current sensing voltage is fed into the non-inverting input of the comparator: whenever the shunt voltage drop goes above the value set via the PWM, the comparator output gets pulled to GND and the output is turned off.
The current limiting resolution though is limited to increments of 4.12mA by the 8 bit PWM resolution of the micro controller.
By pushing the channel current limiting PWM signal down to 0% you are actually disabling the channel.
Unlike the FlexiPower this design has no remote controll yet.
(Partly copied from ROBERTO LO GIACCO)
Manny thanks to Dave from EEVBLOG with his Power Suply series: http://www.eevblog.com/files/uSupplyBenchRevC.pdf
And to ROBERTO LO GIACCO with his FlexiPower supply