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| LDO current limiter |
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| flowib:
LM334 plus 2SC6144 may be what your looking for. The 334 can be used to precicely control a NPN transistor. And the 334 has a rather low compliance voltage of 1V. If you are looking for a constant voltage supply with LDO properties and current limiting, the MIC5156 is available in DIP8 and does 1.25-30V |
| ledtester:
--- Quote from: --Oz-- on August 27, 2022, 08:52:30 pm ---Out of curiosity of your link info, I found some LDO's and they all have the Vfb reference to ground, connected them up as normal to verify they were was working (they are brand new). Then tried the info in your link, none of them worked, I think its because the way most regulators Vref is tied to ground, where the lm317 and a few others are not. I tried these three MIC49150WR MIC29152WU MIC29502BU They simplify would not regulate, tried 100mA and 1A shunt resistors, Thoughts? --- End quote --- What exactly is your circuit? You might be running into this caveat mentioned in the Microchip paper: --- Quote ---There is an important requirement for this circuit: the minimum voltage required for proper operation (2.5V) must be provided between the IN and GND terminals. To satisfy that condition, choose an ROUT value that allows 2.5V to 5.5V between IN and GND. When driving a load of 100Ω maximum with VCC at 5V, for example, the device functions properly with ROUT above 60Ω. That value allows a maximum programmable current of 1.5V/60Ω = 25mA. Voltage across the device then equals the minimum allowed: 5V - (25mA × 100Ω) = 2.5V. This IC can source up to 500mA. --- End quote --- |
| Zero999:
--- Quote from: flowib on August 28, 2022, 12:36:38 am ---LM334 plus 2SC6144 may be what your looking for. The 334 can be used to precicely control a NPN transistor. And the 334 has a rather low compliance voltage of 1V. If you are looking for a constant voltage supply with LDO properties and current limiting, the MIC5156 is available in DIP8 and does 1.25-30V --- End quote --- Adding a transistor increases the voltage headroom requirement. Bear in mind the LM334 has a positive temperature coefficient. It can be countered by adding a diode, but that increases the voltage headroom further. https://www.ti.com/lit/ds/snvs746e/snvs746e.pdf |
| magic:
Not a problem, because the 1.7V minimum applies to the supply voltage required for the circuit to work. OP's supply is 5V. OP's problem was dropout voltage, which is laughably small for this circuit: just the PNP saturation voltage plus approximately 64mV across the current sense resistor. A potential problem is the "approximately" part, because the exact voltage regulated by the chip increases 0.2mV/°C from 64mV at 25°C. |
| --Oz--:
--- Quote from: ledtester on August 28, 2022, 01:43:53 am ---What exactly is your circuit? You might be running into this caveat mentioned in the Microchip paper: There is an important requirement for this circuit: the minimum voltage required for proper operation (2.5V) must be provided between the IN and GND terminals. To satisfy that condition, choose an ROUT value that allows 2.5V to 5.5V between IN and GND. When driving a load of 100Ω maximum with VCC at 5V, for example, the device functions properly with ROUT above 60Ω. That value allows a maximum programmable current of 1.5V/60Ω = 25mA. Voltage across the device then equals the minimum allowed: 5V - (25mA × 100Ω) = 2.5V. This IC can source up to 500mA. --- End quote --- My circuit I tried all three of the MIC regulators I posted above, I first connected them as normal CV and tested to make sure they worked normal mode, they are all brand need, just checking for piece of mind. Then I connected like the picture below. I set the resistor to CC at 100mA first, then 1A (changing the shunt resistor). I first tried Vin=5V and played with a variable 2W 10 turn pot (testing the 100mA), it just would not CC anywhere. Retested at 1A shunt resistor, I tried up to Vin=10v and no luck. I then tried just shorting the CC output to ground and played with Vin, same, no CC, this method works with the lm317. I reconfigured it to normal VC mode and working, again to have piece of mind. Thanks again for the link. The LD1085 should fit my application, but am still curious why 95% of linear regulators dont show CC mode in their datasheet (like the lm317 does), weird when it could sell more parts. |
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