Electronics > Beginners
L200 and UA741
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mike_mike:
Dear Forum,

I built the attached schematic on a home made PCB. When there is no load on the output, the output voltage varies from about 2.77V to 30V. But when I connect a load (12V, 20W bulb), the output voltage goes down to 0.14V and the current is about 0.18A. If I rotate the 100K potentiometer there nothing is happening.
I also noticed that the UA741 is heating up while the load is connected.
I also checked the PCB and there are no bridges.
 
What should I do to make this project working ?

More details: input voltage about 40Vdc, output varying between 2.77 and about 30V, the voltage on the 0.1ohm resistor while the load is connected is 0.02V.
Hopkins:
Do not know how to help me? About the knowledge I'm looking for, I'm following up on sharing this information.
mike_mike:
Please delete this topic.
The project has been abandoned.
bson:
What's the input voltage?  What happens if you use say a 1k resistor load?
mike_mike:
I am using a 24V/160VA power transformer.
If I use as load an 1K resistor and if the output voltage is 25.1Vdc, then the voltage does not drop.
If I am powering a 24V/40W light bulb, the output current is 0.36A, and the ouput voltage drops to 0.7V.

I also obtained the following voltages:
1. LM741
a.pin 7 to pin 4
no load = 31.2V
load = 29.9V
b. pin 2 to 3
no load = 1.1mV
load -1.172V - with 100k pot completely in one direction
c. pin 2 to 3
no load = 1.1mV
load -43.9mV - with 100k pot completely in other direction

2. Voltage across R3
no load 0.3mV
load 34.8mV

3. L200
a. pin 5 to GND
no load 25.1V
load 0.8V
b. pin 2 to GND
no load 24.8V
load 2.0V

I attached the layout for this power supply.
I also checked with a new 741, and the power supply is still not working correctly.
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