Its a ltc3780 buck boost converter. It has a 500k pot for voltage control and 250k pot for current limiting.... So any ideas how can I digitally achieve this. Thanks so much :')Why does the buck/boost converter need such a high value pot?
Thanks for the replybertus said:Hello,
Do you have the intended schematic you want to use?
On the webpage I do not see the 250K and 500K you mention:
Thanks for the replyI see a 487K fixed resistor in the voltage output sense feedback loop, but not a pot. Also, most digital pots cannot run between +48V and GND. What is the max output voltage you are trying for?
The VOS+ feed resistor R4 (10Ω) and C47 (0.1u) (as in the datasheet) would certainly affect the feedback loop frequency response, but I'd be surprised if reducing R8 and R7 by a factor of 100 even would make much difference. The reactance of C47 at the operating frequency is only a few Ohms, so if R7 were, say, 5k that shouldn't greatly affect the phase shift which R4 and C47 produce. That's theory, of course .both the voltage and current set circuits have capacitors in them that are part of the control loop frequency compensation, and varying the resistors shifts the corner frequencies. Whether or not this will send the regulator into oscillation can be calculated by someone much better at this than me. I'd start by replacing R8 with a 10K pot and adjusting it all over the place to see what happens.
My money says not, unless (a) you can source digital pots which can withstand 30V (or whatever your max output will be) and (b) the regulation will work with pot resistances ~10k or less.So is it possible or not?
Ok thanks :') is there a good guide to make a switching programmable variable psu with a max voltage of around 30v?My money says not, unless (a) you can source digital pots which can withstand 30V (or whatever your max output will be) and (b) the regulation will work with pot resistances ~10k or less.
Do you have a real schematic?The pots values make zero sense to me.
Having said that, if you still want to go down the path, attenuate the high voltage and then amplify it with an opamp whose gain is controlled by the pot.
I don't know if that part is a good solution or not, but thought I would mention itMicrochip's MCP41HVX1 36V Digital Potentiometers are devices that have dual power rails (analog and digital). The analog power rail allows high voltage on the resistor network terminal pins. The analog voltage range is determined by the V+ and V– voltages. The maximum analog voltage is +36V, while the operating analog output minimum specifications are specified from either 10V or 20V. As the analog supply voltage becomes smaller, the analog switch resistances increase, which effect certain performance specifications. The system can be implemented as dual rail (±18V) relative to the digital logic ground (DGND).
Haven't checked, but people here usually advise that it's cheaper/easier to buy one than build one.is there a good guide to make a switching programmable variable psu with a max voltage of around 30v?
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