Hydrogen PWM
From emboxit
- http://www.hhocarfuelcell.com/pwm-circuit/variable-frequency-pwm.php
- http://reyhidrogeno.blogspot.gr/2010/10/efie-digital-diagramas-electronicos.html
- http://www.hhocarfuelcell.com/pwm-circuit/pulse-width-and-frequency-control.php
- http://www.braaifest.com/h202-generator.htm
- http://www.hho-plus.com/product.php?id_product=15
This is a slightly modified version of the first PWM. The basic circuit is the same. Some component values have changed. And it's laid out specifically to fit in a Velleman G106 sealed die cast aluminum enclosure measuring 4.5" L x 2.5" W x 1.25" H. Bud and Deltron also make very nice die cast aluminum cases. U1 is a LM324N quad op-amp. U1A and U1B form a triangle wave generator. The output voltage swing is approx. 1/3-2/3 Vcc. The output is fed to comparator U1C which turns it to square wave based on the threshold voltage at pin 10. The duty cycle threshold is set by VR1. R6 and R7 are calibrated to give full range duty cycle adjustment of VR1. The voltage reference for R7 is normally held at Vcc by the output of current limiting error amp U1D. Gain is set at 1000 (subject to change depending on how stiff I want the current to limit). Any time the source of Q1 draws current a voltage drop occurs across R12. 80 amps will give 120mV, the max setting on VR3. If the voltage drop across R12 exceeds the preset value of VR3, the comparator drops the PWM duty cycle until the average is just less than the preset value. C4 ensures that the current limiting is average not peak. R12 is just a 6" piece of #14ga stranded copper wire. The leads are connected to the Source of the MOSFET, AT THE SOURCE TERMINAL, and to the common ground, AT THE COMMON GROUNDING POINT. Also, the PC board terminal at the junction of C4/VR3 connects directly to the common ground and the PC board terminal for R10 connects directly to the MOSFET Source terminal. These steps are very important to observe as unwanted oscillations and instability can occur.
