Hi,
Anyone can shed light, measuring of load i can adjust the lt1085 with turn pot just fine.
When i set it to say 13v without load, once small load is connected voltage drops to 2v or so
Im using a ebay lm317 board and did put a 10000uf cap at the input
Please anyone can chime in.
Anyone can shed light, measuring of load i can adjust the lt1085 with turn pot just fine.
When i set it to say 13v without load, once small load is connected voltage drops to 2v or so
Im using a ebay lm317 board and did put a 10000uf cap at the input
Please anyone can chime in.
The regulator will drop out if (Vin-Vout)*Iload is too high, and it isn't heat sinked.
The LT1083,4,5 family are quasi "low-drop out regulators" (LDO) and as such needs a capacitor on the output for stability. 100uF aluminum electrolytic should be Ok. See Linear Tech's data sheet.
The LT1083,4,5 family are quasi "low-drop out regulators" (LDO) and as such needs a capacitor on the output for stability. 100uF aluminum electrolytic should be Ok. See Linear Tech's data sheet.
its a basic design with turnpot for adjust and a cap at output.
even connecting to power a 3.3v regulator not connected to any load causes a drop.
it fine without amything connected.
vin 22v load i am powering maybe 13v, 1 - 2 a.
big heatsink but not warm, just drops on anything connected.
even connecting to power a 3.3v regulator not connected to any load causes a drop.
it fine without amything connected.
vin 22v load i am powering maybe 13v, 1 - 2 a.
big heatsink but not warm, just drops on anything connected.
You probably realise that provided there are no faulty connections or fake chips, this behaiviour is quite impossible.
DUG,
sorry i purchased the board from ebay (very basis design), it is a lm317 reg so i swapped it out. Basic bridge to a cap to Vin, 1 resistor 22uf cap and a pot.from Vout and V adj.
ticknpop,
Thanks you are right that i studied the schematic for the LT1085 it need a cap at output which the board doesnt have. I have placed a 2200uf cap but frustratingly, it is the same.
The Lt was purchased from element14 so not a fake, could it be damaged. This is the 2nd LT one i replaced. FWIW, may not be the reg.
The adj resistor is a 1/4w, could this be causing the problem?
Thanks once again.
sorry i purchased the board from ebay (very basis design), it is a lm317 reg so i swapped it out. Basic bridge to a cap to Vin, 1 resistor 22uf cap and a pot.from Vout and V adj.
ticknpop,
Thanks you are right that i studied the schematic for the LT1085 it need a cap at output which the board doesnt have. I have placed a 2200uf cap but frustratingly, it is the same.
The Lt was purchased from element14 so not a fake, could it be damaged. This is the 2nd LT one i replaced. FWIW, may not be the reg.
The adj resistor is a 1/4w, could this be causing the problem?
Thanks once again.
Is the single resistor 120R or 240R?
These regulators need a minimum load so 120R is recommended...otherwise the output voltage will rise above what is set and will go back to a regulation point when minimum current requirements are met.
The pot should be as shown, not from Vout to Vadj.
See .jpg (caps not shown)
These regulators need a minimum load so 120R is recommended...otherwise the output voltage will rise above what is set and will go back to a regulation point when minimum current requirements are met.
The pot should be as shown, not from Vout to Vadj.
See .jpg (caps not shown)
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Hi DUG,
The resistor load is important, i saw some schematics and now have a better understanding. It was strangely a 100r resistor and not 120r
I didnt mention i had in connected as a pretracking regulator, running13v out to a 3.3v fixed regulator to power both a 13v and a 3.3v required as i didnt understand that as a pretracking reg and load changes needed, i will thus need to change the resitor values accordingly
As such, i will need at least a 1.2k load restor and change the pot to a higher value 20k.
Once again thank you in guiding towards a new understanding, i hope im on the right track now
The resistor load is important, i saw some schematics and now have a better understanding. It was strangely a 100r resistor and not 120r
I didnt mention i had in connected as a pretracking regulator, running13v out to a 3.3v fixed regulator to power both a 13v and a 3.3v required as i didnt understand that as a pretracking reg and load changes needed, i will thus need to change the resitor values accordingly
As such, i will need at least a 1.2k load restor and change the pot to a higher value 20k.
Once again thank you in guiding towards a new understanding, i hope im on the right track now
The resistor in the upper leg is NOT a critical value -- the minimum current can be derived by just loading the regulator to 5mA. In fact, you can get better transient and noise performance by experimenting with values of R1 and R2, and placing a cap across R2...
The LT108X family have thermal protection, so they will cycle off if not heat-sinked and the (input-output voltage limit) * load current is broached. See page 12 of the datasheet.
And again, it's a low dropout regulator, so must be run with an output capacitor for stability.
The LT108X family have thermal protection, so they will cycle off if not heat-sinked and the (input-output voltage limit) * load current is broached. See page 12 of the datasheet.
And again, it's a low dropout regulator, so must be run with an output capacitor for stability.
As jackinnj says the "top" resistor can be a different value.
It just depends on how much you will allow variations of ADJ current to affect your selected voltage.
I use these types with the resistor values able to draw the maximum minimum current...10mA (from data sheet)
This way the output can be checked before a load is connected.
But that is just me.
🙂
It just depends on how much you will allow variations of ADJ current to affect your selected voltage.
I use these types with the resistor values able to draw the maximum minimum current...10mA (from data sheet)
This way the output can be checked before a load is connected.
But that is just me.
🙂
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