cupoftea
Advanced Member level 5
Hi,
A customer has sent us a 1kW power supply and wants us to adjust it so that it clamps its output current to 34A maximum. However, the customer has requested, that if we can, can we make it clamp its output current to an increasing value if the output voltage is lower….. Ie, at 28V output, clamp the output current to 34A, and at 18V output, clamp it to 38A….and the clamp current level being linear between those two points.
The attached (PDF schem and LTspice sim is what we have so far. The ringed current clamp is the bit that we have added in.) BTW, i have to confess that the BOM they supplied us with does not have a value for R35....So we have guesstimated what it probably is. (its a DCDC module and we cant break it open)
This one is a long , messy story….customer originally supplied the PSU not realising it was supposed to be a battery charger….so now wants to modify it for battery charging.
The only way we can control this PSU is via the TRIM pin…..thats the only thing we can access.
Can you agree that , given the attached shown circuitry, there is no way that the current clamp level can be made to increase as the output voltage reduces?
May you also agree, the following?...
The customer thinks that changing U8 from an integrating error amplifier to an error amplifier with a DC feedback path (ie a high value resistor from opamp output to inv, as well as a capacitor from opamp output to inv) will mean more chances of avoiding instability.
Do you agree that this doesn’t add up?
A customer has sent us a 1kW power supply and wants us to adjust it so that it clamps its output current to 34A maximum. However, the customer has requested, that if we can, can we make it clamp its output current to an increasing value if the output voltage is lower….. Ie, at 28V output, clamp the output current to 34A, and at 18V output, clamp it to 38A….and the clamp current level being linear between those two points.
The attached (PDF schem and LTspice sim is what we have so far. The ringed current clamp is the bit that we have added in.) BTW, i have to confess that the BOM they supplied us with does not have a value for R35....So we have guesstimated what it probably is. (its a DCDC module and we cant break it open)
This one is a long , messy story….customer originally supplied the PSU not realising it was supposed to be a battery charger….so now wants to modify it for battery charging.
The only way we can control this PSU is via the TRIM pin…..thats the only thing we can access.
Can you agree that , given the attached shown circuitry, there is no way that the current clamp level can be made to increase as the output voltage reduces?
--- Updated ---
May you also agree, the following?...
The customer thinks that changing U8 from an integrating error amplifier to an error amplifier with a DC feedback path (ie a high value resistor from opamp output to inv, as well as a capacitor from opamp output to inv) will mean more chances of avoiding instability.
Do you agree that this doesn’t add up?
Attachments
Last edited: