M8单片机恒流型数字电子负载

kazuyuki · 发表于 2014-12-27 11:30

kirich 发表于 2014-12-27 07:30
Excuse me, can I have a current firmware 15A ± 15mA and (or) 30A ± 30mA?
I would like to make t ...

if you want increase the current, it is not need change the firmware. You can just decrease the sampling resistor and and add more MOS FET, keep the sample voltag in 0~0.25v, then re-configure.

kazuyuki · 发表于 2014-12-27 11:42

kirich 发表于 2014-12-27 07:30
Excuse me, can I have a current firmware 15A ± 15mA and (or) 30A ± 30mA?
I would like to make t ...

I am not sure you can understand chinese. some people has done some trial test in it. You can see this https://www.yleee.com.cn/forum.php?mod=viewthread&tid=12230&highlight=m8v6. He has multi MOS FET from 1 to 4, and power load increase into the firmware limit 15A. I have not tested it, and I still did not know if the firmare can reach 30A。Maybe you can set the current to 30A, but the display is still in 15A.

sorry my poor english. I wish you can understant what I mean.

The firmware's source code is open now. You can download it an change what you want.

kirich · 发表于 2014-12-27 16:44

本帖最后由 kirich 于 2014-12-27 17:01 编辑

No, you do not understand.
Strengthen the current and the number of transistors is not a problem.
I saw these schemes.
The firmware does not give the correct current.
PWM is changed from 0 to 100% But it does not change in the range of 0-15 amps, but only 0-5 Amps.
When installing the current above 5 A PWM signal at the output of the processor does not change, it is already maximal. I tried to download the firmware to 5 amps, but I began to work properly indicator (firmware for 2402 and I use 2004). There's just shifted range 0-100% PWM was at 0-5 amps, and therefore 0-7.5 amps.
But anyway, if I expose the display 10 amps (for example), I have a 5 anyway. If you change the current measurement resistor, it will be incorrect readings and incorrect installation.

I can read Chinese responses online, English is more convenient,

kirich · 发表于 2014-12-27 17:00

I understand that it is difficult to communicate in different languages.
I will try to explain in a table.
PWM output processor. Display (installation)
0% 0 Amp
20% 1 Amp
40% 2 Amp
60% 3 Amp
80% 4 Amp
100% 5 Amp
100% 6 Amp
100% 7 Amp
and so on up to 15 amps

A should be
0% 0 Amp
20% 3 Amp
40% 6 Amp
60% 9 Amp
80% 12 Amp
100% 15 Amp

If you replace only the resistor current sensor, there will be false readings on the display.

kirich · 发表于 2014-12-27 17:15

kazuyuki 发表于 2014-12-27 11:42
I am not sure you can understand chinese. some people has done some trial test in it. You can see ...

A processor learns that transistors become more and can be given to put more than 5 amps?

kazuyuki · 发表于 2014-12-27 18:40

kirich 发表于 2014-12-27 17:00
I understand that it is difficult to communicate in different languages.
I will try to explain in ...

I think you have reached the limit of MOS FET. The PWM out is not higher then 5v. When PWM reached it, the MOS FET could not drive more ouptu current . maybe you MOS FET's Vgs is too high or the Rds is too high. This make output can not higher then voltag/Rds. I suggest you add one more operational amplifier to increase the PWM output voltag to MOS's gate. Since the original PWM output is 5v, may you should connect the amplifier's power to higher, and change the Amp's gain.

kirich · 发表于 2014-12-27 19:10

kazuyuki 发表于 2014-12-27 18:40
I think you have reached the limit of MOS FET. The PWM out is not higher then 5v. When PWM reached ...

No, you do not quite understand correctly.
After setting the current more than 5 amps output processor nothing changes.
Ie when I select the current setting of more than 5 amps, the processor does not change anything.
Change resistor current or the number of transistors will not work right? I gave the above table.
After setting the current 5 amps and a further increase in the processor continues to produce the maximum.
Rather processor peaks not at 15 amps and 5 amps.

I understand that it is necessary to modify the firmware of the processor that would fill the PWM was not at the facility 5 Amps and 15 Amps at the facility.
Saturation of the transistor is not to blame.

kirich · 发表于 2014-12-28 00:12

本帖最后由 kirich 于 2014-12-28 00:35 编辑

I'll try to explain once again.
No problems getting the output current of 15 amperes.
If I add two gain stage current, the current will be 15 amperes.
But when you install the current, the indicator will be displayed only 0-5Amper.
When you change the current in the range of 5-15 amps, the processor does not change the output, since the PWM output PWM is already 100%.
The problem occurs when you set up the necessary current.

Set current    PWM (PWMA)    Voltage op amp comparison
On display    On pin PB1 MCU       Pin 3 U51A (LM358)
0.000As          0%                               0 V
1.000As          20%                               0.05 V
2.000As          40%                               0.10 V
3.000As          60%                               0.15 V
4.000As          80%                               0.20 V
5.000As          100%                            0.25 V
6.000As          100%                            0.25 V
15.000As       100%                            0.25 V

Even if I add the gain of the current (as in the diagram above), then I get 15 Amps current. But I have to display the current will be less than 3 times, because the change occurs only in the range of adjustment 0-5Amper all.

Adjusting the PWM and the input voltage of the operational amplifier should look like -

Set current    PWM (PWMA)    Voltage op amp comparison
On display    On pin PB1 MCU       Pin 3 U51A (LM358)
0.000As          0%                               0 V
3.000As          20%                               0.05 V
6.000As          40%                               0.10 V
9.000As          60%                               0.15 V
12.000As       80%                               0.20 V
15.000As       100%                            0.25 V
Then the adjustment range is fully used.
,,

In a range of settings (no measurement) 5-15 Ampere current MCU does not change anything on pin PWMA (PB1).

If the adjustment range was up to 30 amps, it would look like this -
Set current    PWM (PWMA)    Voltage op amp comparison
On display    On pin PB1 MCU       Pin 3 U51A (LM358)
0.000As          0%                               0 V
6.000As          20%                               0.05 V
12.000As       40%                               0.10 V
18.000As       60%                               0.15 V
24.000As       80%                               0.20 V
30.000As       100%                            0.25 V

The voltage at the pin 3 of the operational amplifier is used to compare the voltage at the current measuring resistor.
If I add additional transistors as the scheme, I have a 3-fold increase in the output current, but it will be three times larger than the set. When installing additional transistors will be so -
Set current    output current
on display       really
1.000As             3.000 Amp
2.000As             6.000 Amp
3.000As             9.000 Amp
4.000As             12.000 Amp
5.000As             15.000 Amp
6.000As             15.000 Amp
15.000As          15.000 Amp

kirich · 发表于 2015-9-18 19:35

本帖最后由 kirich 于 2015-9-18 19:44 编辑

If anyone is interested, here is my version of the implementation of the instrument.
Current up to 15 Amps (can somebody share firmware of up to 30 amps).
Maximum power of 400 watts.