Power supply and automatic lock

Thread Starter

sugandha sharma 1

Joined Apr 24, 2019
11
Hi All

I have designed a circuit but. I have tested 12V to 5V supply, it is working correctly but 12V to 3.3V is not converting and ASM1117 has got burnt. I am not able to identify the issue. Kindly help me in this.
12Vto3.3V.png
 

metermannd

Joined Oct 25, 2020
332
Is there any reason why you can't go from 12V to 5V to 3.3V?

The 7805 has to convert a 7V drop (times output current) to heat, but the 3.3V regulator is being asked to convert 8.7V (times output current) to heat.

But if you feed the 3.3V regulator from the 5V rail, then you only need worry about 1.7V (times output current).
 

Thread Starter

sugandha sharma 1

Joined Apr 24, 2019
11
Is there any reason why you can't go from 12V to 5V to 3.3V?

The 7805 has to convert a 7V drop (times output current) to heat, but the 3.3V regulator is being asked to convert 8.7V (times output current) to heat.

But if you feed the 3.3V regulator from the 5V rail, then you only need worry about 1.7V (times output current).
Let me correct this and check.
 

Sensacell

Joined Jun 19, 2012
3,064
If you cascade the 5V regulator into the 3.3V you still burn the 2 Watts, but at lease it's divided between the two parts.

The next level of efficiency (cool running) is to switch over to a switching regulator. (more expensive, noisy, but greater conversion efficiency)
 

crutschow

Joined Mar 14, 2008
30,791
You can also add a power resistor in series with the 3.3V regulator input to dissipate some of the heat.
For example a 3W, 27Ω, resistor in series will drop 6.75V and dissipate 1.7W @ 250mA, leaving 0.5W to be dissipated by the regulator, which should keep it at an acceptable temperature.
Note that the resistor will get quite warm.
 

Thread Starter

sugandha sharma 1

Joined Apr 24, 2019
11
You can also add a power resistor in series with the 3.3V regulator input to dissipate some of the heat.
For example a 3W, 27Ω, resistor in series will drop 6.75V and dissipate 1.7W @ 250mA, leaving 0.5W to be dissipated by the regulator, which should keep it at an acceptable temperature.
Note that the resistor will get quite warm.
I have soldered components for supply only. Issue is there only. No more components I have soldered apart from power supply right now.
 

Thread Starter

sugandha sharma 1

Joined Apr 24, 2019
11
If you cascade the 5V regulator into the 3.3V you still burn the 2 Watts, but at lease it's divided between the two parts.

The next level of efficiency (cool running) is to switch over to a switching regulator. (more expensive, noisy, but greater conversion efficiency)
I have soldered components for supply only. Issue is there only. No more components I have soldered apart from power supply right now.
 

crutschow

Joined Mar 14, 2008
30,791
I have soldered components for supply only. Issue is there only. No more components I have soldered apart from power supply right now.
By that, do you mean there is no output load on the supply?

If so, then you problem is likely a wiring mistake.
Carefully check the wiring against the schematic.
 

Thread Starter

sugandha sharma 1

Joined Apr 24, 2019
11
By that, do you mean there is no output load on the supply?

If so, then you problem is likely a wiring mistake.
Carefully check the wiring against the schematic.
Problem is solved now. I am converting 5V to 3.3V now.
New problem is I am able to program Atmega328P but not able print the data on serial monitor through FTDI. Same code with FTDI is working on other hardware PCB but not with my PCB.
 

Thread Starter

sugandha sharma 1

Joined Apr 24, 2019
11
If you cascade the 5V regulator into the 3.3V you still burn the 2 Watts, but at lease it's divided between the two parts.

The next level of efficiency (cool running) is to switch over to a switching regulator. (more expensive, noisy, but greater conversion efficiency)
Problem is solved now. I am converting 5V to 3.3V now.
New problem is I am able to program Atmega328P but not able print the data on serial monitor through FTDI. Same code with FTDI is working on other hardware PCB but not with my PCB.
 
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