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| 10 Amps power supply with LM723 |
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| iMo:
1. What was the problem, could you tell us? 2. See my previous post with 500ohm pot's wiper value (measured from its low side) vs. current limit. In the mid position it shows 1A limit. It is a simulation only.. |
| mike_mike:
The problem was the PNP transistor. There was a bridge between the C and E of this transistor, and I did not saw it when I made the inspection... Later Edit: If I use 2 220R resistor in series instead of the 500R pot, then the output current is about 1A. The connection between the 2 200R resistor is connected to the point were the pot wiper was connected before. I do not have any other 500R pot or trimmer to check if the first one was faulty, can there be used 1K pot instead of 500R pot ? I checked again with 1k pot for current limit, and at the half of the pot, the current is 0A. Only on the other half the current starts to rise from 0A to 3A. |
| iMo:
In case of 1k pot you have to increase the 4k7 resistor. I would put, say, a 22k trimmer instead of the 4k7, set the 1k pot's wiper to the top position and set the minimal current limit with the 22k trimmer. Replace the 22k trimmer with a close valued resistor finally. For example a simulation with 10k the top resistor, 1k pot, 120ohm bottom, AND a 10k resistor from pot's wiper to gnd POT's wiper CLimit top 23mA mid 1.8A down 3.8A |
| mike_mike:
I checked using a 22k trimmer, the 1k pot, and I found that the proper value is around 12.7K for the trimmer. The current limit starts from 0A and goes up to 3.31A. I found that when I rotate the pot, it starts from 0A, then if I rotate it a very little then the current suddenly increase to more than 200mA, and there is a very little "space" on the pot for 1mA or 5mA. Is that normal ? Later Edit: only now I have saw your edit. |
| iMo:
The pot setting is highly none-linear. It follows the Vbe characteristics. The 10k (or similar) from wiper to gnd could make it "more linear".. PS: or use 1k "logarithmic" potentiometer. |
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