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Three functions for a Mosfet: CRC Filter, Soft Start and i-sense. Will it work or not
Three functions for a Mosfet: CRC Filter, Soft Start and i-sense. Will it work or not
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Old 12th April 2021, 03:37 PM   #31
Avelino Sampaio is offline Avelino Sampaio  Brazil
diyAudio Member
 
Join Date: Aug 2019
Location: Rio de Janeiro
Hi

I decided to implement a safety system, in case the power transistor suffers a short circuit.

image 1: 10v output voltage, with 1A load. Closing short between collector and emitter.

image 2: 10v output voltage, without load. Closing short between collector and emitter.

image 3: Start psu with collector and emitter shorted. Without load resistor.

image 4: Start psu with collector and emitter shorted. with 8R load resistor at the output.

image 5: Updated schematic.
Attached Images
File Type: jpg short_transistor_1A.jpg (431.3 KB, 48 views)
File Type: jpg short_transistor_0A.jpg (531.1 KB, 45 views)
File Type: jpg psu_start_short_transistor_0A.jpg (394.8 KB, 44 views)
File Type: jpg psu start_short_transistor_1A.jpg (452.0 KB, 45 views)
File Type: png Diy_lab_723_v3.png (268.9 KB, 46 views)
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Old 18th April 2021, 03:36 PM   #32
Avelino Sampaio is offline Avelino Sampaio  Brazil
diyAudio Member
 
Join Date: Aug 2019
Location: Rio de Janeiro
MCP6002

I had a problem with the regulation of the CC, due to a limitation of the MCP6002. Due to the low value of the full-swing (30khz), the opamp output would turn off, before the full adjustment range. For example, for a 1.7A load, I was only able to get an adjustment from 0 to 0.8A. Exceeding 0.8 the opamp cut the output voltage, releasing the load to 1.7A.

Analyzing the graph (image 1), I could see that lowering the supply voltage to approximately 2v, could extend the full-swing considerably. To lower the voltage of the MCP, I used a blue led (LD7), as you can see in the schematic. The MCP6002 started to operate at 60khz.

I noticed that the MCP was trying very hard to keep things under control and so I decided to change the capacitor C22 (pin 13 of the LM723) from 1nf to 100nf and the magic worked. MCP started to operate close to 8.5 kHz, operating only on the pulse width. Observe in image 2, the CC set to 100ma (output voltage 14v with a load pulling 1.7A). See the oscilloscope at the base of Q5 showing the MCP operating at approximately 8.5Khz. Now look at image 3, where CC was set to 1A. The signal at the base of Q6 with the smallest pulse width, staying close to 8.5 kHz.

I decided to keep the MCP6002 operated with low voltage (2.1v), ensuring a high pull-swing.
Attached Images
File Type: png swing_mcp6002.png (37.9 KB, 16 views)
File Type: jpg mcp_2.jpg (556.7 KB, 6 views)
File Type: jpg mcp_3.jpg (573.0 KB, 8 views)
File Type: jpg mcp_4.jpg (689.9 KB, 9 views)
File Type: png Diy_lab_723_v4.png (275.3 KB, 15 views)
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Old 22nd April 2021, 01:23 PM   #33
Avelino Sampaio is offline Avelino Sampaio  Brazil
diyAudio Member
 
Join Date: Aug 2019
Location: Rio de Janeiro
Hi!

Load Transient Testing

Today was the day to choose the output capacitor. As a parameter, I stipulated that the peak-to-peak voltage (between the overshoot and the undershoot) was a maximum of 8% (load at 2A), for the output voltages of 5v and 3.3v. I started with a 100uf capacitor but the one that best met the parameter was 220Uf.

Image 1:

- 1khz frequency (pulse set to 100us)
- 3.3v output voltage / 2A load current

Image 2:

- 1khz frequency (pulse set to 100us)
- output voltage 5v / load current 2A

Image 3:

- 1khz frequency (pulse set to 100us)
- output voltage 20v / load current 2A
Attached Images
File Type: jpg 3.3_2A_100u_2.jpg (533.9 KB, 9 views)
File Type: jpg 5v_2A_100u_2.jpg (532.8 KB, 8 views)
File Type: jpg 20v_2A_100u_2.jpg (498.5 KB, 7 views)
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Old 25th April 2021, 11:20 AM   #34
Avelino Sampaio is offline Avelino Sampaio  Brazil
diyAudio Member
 
Join Date: Aug 2019
Location: Rio de Janeiro
Protection system and the use of batteries in the output terminals.

Due to the protection system, in the event of a short-circuit of the power transistors, I had to insert an additional protection, for charging my batteries.

Test 1 - connect the battery to the input terminals, with the PSU off.

With the battery's own energy, the SCR TR3 is activated, keeping the MOSFET M1 (IRF6218) in the cut. The PSU will only turn on fully when the battery is removed from the terminals. See in image 1, that there will be a consumption of 64ma of the battery.

Test 2 - charging the battery, with the PSU shutdown in the middle of the process.

SCR TR3 will also be activated here, blocking the M1 Mosfet. The PSU will only turn on fully when the battery is removed from the terminals.

Test 3 - battery connected to input terminals with psu at 5v.

Once again the defense system (d5, d6, d7) worked perfectly and nothing was affected. Removing the battery, return to 5v.

Follows the updated scheme.
Attached Images
File Type: jpg Battery_psu_off.jpg (621.0 KB, 7 views)
File Type: png Diy_lab_723_v5.png (282.4 KB, 11 views)
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Old 26th April 2021, 12:29 PM   #35
Avelino Sampaio is offline Avelino Sampaio  Brazil
diyAudio Member
 
Join Date: Aug 2019
Location: Rio de Janeiro
Finished Tests:

CRCRC filter: Very good.
Soft Start: Very good.
Filter with capacitance multiplier for Lm723: Very good.
CV with low output noise: Good (It will be even better with the PCB and adequate cabling).
CC: Good.
Load transient:Very good.
Quick shutdown of PSU - short-circuit power transistors: Good.
Cooling system, with limit temperature protection: Very good.
Construction of the output voltage, when turning on the PSU: Very good.
Quick deconstruction of the output voltage, when turning off the PSU: Very good.

Next step: building the pcb
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Old 6th May 2021, 10:20 AM   #36
Avelino Sampaio is offline Avelino Sampaio  Brazil
diyAudio Member
 
Join Date: Aug 2019
Location: Rio de Janeiro
Hi

Follows schematic, with some corrections in the project. Follow the link to open it in the digkey application.

Lm723_Digkey

I will assemble the PCB by EasyEDA. Follows schematic and file.
Attached Images
File Type: png Diy_lab_723_v6.png (285.2 KB, 9 views)
File Type: png Schematic_PSULinear_Lab_LM723_2021-05-06.png (190.3 KB, 10 views)
Attached Files
File Type: zip PSULinear_Lab_LM723_2021-05-06.zip (61.6 KB, 2 views)
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