Current linearity test experiment of transistor PWM drive

Equipment: transistor, resistor (500R), perforated board, oscilloscope, LED (3.3V-3.6V), stm8 microcontroller (generating PWM signal), adjustable power supply with current display.
Method: The circuit hardware is the same as that of experiment 4. The signal source uses stm8 to generate a 243hz adjustable duty cycle PWM signal.
Circuit diagram: None
Test environment: At room temperature
Compilation environment: IAR

Program
Initialization program: 
    TIM2->PSCR = 0x00;    
    TIM2->ARRH = 0xff;
    TIM2->ARRL = 0xff;
    TIM2->CCMR1 = 0x60;
    TIM2->CCER1 = 0x01;
    TIM2->CCMR1 |= 0x08; 
    TIM2->CCR1H = 0;
    TIM2->CCR1L = 0;

The power supply voltage is 5V, the test resolution is 8 bits, 0-ffff 
TIM2->CCR1H Duty Cycle Current Base Average Voltage
00 0% 0.00A 0V
01 1% 0.01A 85mV
10 6.8% 0.04A 312mV
20 12.6% 0.08A 586mV
30 19.4% 0.12A 795mV
40 25.2% 0.16A 1.06V
50 31.4% 0.19A 1.33V
60 37.9% 0.23A 1.61V
70 43.7% 0.27A 1.88V
80 49.5% 0.31A 2.14V
90 55.9% 0.35A 2.41V
a0 62.1% 0.39A 2.69V　　
b0 68.0% 0.43A 2.97V
c0 74.8% 0.47A 3.24V
d0 80.6% 0.50A 3.52V
e0 87.4% 0.54A 3.79V
f0 93.2% 0 .58A 4.05V
ff 99.0% 0.62A 4.23V
ff ff 100.0% 0.62A 4.25V

The above data shows that the linearity of duty cycle and current is quite good. Each gear is basically controlled at around 0.04A. If the requirements are not high, there should be no problem using this.

Direct control using voltage

Base control voltage, Collector current
720mV 0.01A
756mV 0.02A
770mV 0.03A
785mV 0.04A
880mV 0.08A
960mV 0.12A
1.00V 0.16A 1.07V
0.19A 1.10V 0.23A 1.20V 0.27A 1.32V 0.31A 1.52V 0.35A
1.76V
0.39A
2.14V 0.43A 2.48V 0.47A 2.80V 0.50A 3.28V 0.54A 3.76V 0.58A 4.37V 0.62A

From the above data, we can see that if the voltage is simply added, although the voltage and current are also proportional, it can be seen that the linearity of voltage and current is not as good as that of PWM, especially when the voltage is low, the slope feels relatively large. Therefore, it is better to use PWM control when using it.