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| CH341A Serial Memory Programmer Power Supply Fix |
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| johnmx:
I bought one cheap chinese CH341A serial memory programmer black PCB (see attached picture). Someone already did the schematic of this board (atached). Source: https://www.onetransistor.eu/2017/08/ch341a-mini-programmer-schematic.html All Vcc connections in the ZIF socket are 3.3V but the CH341A is powered at 5V. So all I2C and SPI signals are 5V while the external memory is powered at 3.3V. There are no limiting series resistors on those signals. One simple solution to fix this issue is to simply bypass the 1117-3.3V regulator. I can use the hot air station to remove the 1117 and then short-circuit the input with the output. My question is, is it safe to just do the short-circuit without removing the 1117 linear regulator? |
| Ian.M:
Not really. A genuine LM1117-3.3V should be OK as there is a 5V version and it isn't a shunt regulator, but who knows what a 'chinesium' 1117 will do. Also, if you want to convert to 3.3V you should not only remove it but patch in a current limiter in its place e.g. a 100mA polyfuse. Why not power the CH341A at 3.3V to get all 3.3V signal levels? Lift the Vcc pin (28), and patch wire it to the V3 pin (9) and the output of the 117 3.3V regulator. |
| johnmx:
--- Quote from: Ian.M on October 14, 2017, 02:34:26 pm ---Why not power the CH341A at 3.3V to get all 3.3V signal levels? Lift the Vcc pin (28), and patch wire it to the V3 pin (9) and the output of the 117 3.3V regulator. --- End quote --- I thought on that solution at first, but it requires a little more work. I need to cut two tracks and place 2 wires. But yes, it is better to do like you say. A lot of serial memories are limited to 3.6V. |
| Ian.M:
No track cuts, just lift pin 28 (easy because its near the board edge with nothing in the way) and run a wire from the lifted pin across to pin 9, and on to the 3.3V regulator output. If in doubt, see the CH341A datasheet: https://components101.com/sites/default/files/component_datasheet/ch341-datasheet.pdf |
| johnmx:
Here is the result. Next Monday I will replace the 0 Ohm R1 with a 100mA polyswitch. Hope this helps other people. |
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