testing troubleshooting inverter

Description: Connect 22k fixed resistors across each transistor base and ground, then connect the leads of a 50K dual potentiometer across these resistors to imitate variations similar to a 10k potentiometer. Remove the 10K resistors connected to the base of each transistor and replace them with 22K resistors, adding two additional 22K resistors from the emitters to ground. The 50K dual potentiometer should be connected across these connections. After soldering the potentiometer in place, confirm the soldering is correct before integrating it into the inverter. When powering the circuit and adjusting the potentiometer, the voltage at the output of TR1 and TR2 should fluctuate. It was previously stated that the dual potentiometer was 50K ohms, but it is actually 15K ohms. Clarification is needed on whether the 22K ohm resistors are still necessary or if a different value is required. Due to the PWM circuit causing the inverter's current consumption to rise to 14 amps, reducing the drive voltage to the gates of the MOSFETs may be a solution. This can be achieved by controlling the base voltage of the buffer transistors through the variable resistor connected between the base and ground of each transistor. Testing with a lamp and ammeter setup is advised, adjusting the 15K potentiometer until the current consumption aligns with the square wave design. During testing with the headlight, ammeter, and PWM circuit, a reading of 2.1 amps was observed, but adjusting the potentiometer did not yield significant changes in current, except for when it was turned nearly all the way to the left, which caused the inverter to stop functioning. The waveform returned upon adjusting the potentiometer to the right, yet the headlight brightness remained unchanged. Limitations in testing waveforms were noted due to the use of a laptop oscilloscope and a homemade probe. Observations indicated that other circuits utilizing the 4017 chip did not include buffer transistors, suggesting a potential removal of these components from the original square wave circuit. In these alternative circuits, the clock input is directly connected to the 4017, with outputs feeding directly to the MOSFET gates through small resistors. It is recommended to maintain a series bulb during testing to protect the MOSFETs from damage. After placing the 22K resistors across the base and ground of both transistors, a headlight ammeter test yielded a reading of 1.80 A, consistent with the square wave circuit's 1.82 A. However, upon checking the waveform at the gate of both MOSFET banks, a corruption was noted in the waveform driven by IC2, which was missing a pulse, while IC1's output was intact. Further examination of the waveform at the diode junctions is necessary to determine if the issue originates from the PWM section or the lamp and base resistor. It is advised to replace the current transformer with a lower power transformer, such as a 12-012/1 amp transformer, before proceeding with waveform checks and testing smaller loads, like a 10-watt 120V lamp.

The described circuit involves the modification of a PWM inverter setup, focusing on controlling the output current and voltage through the adjustment of transistor base resistances. The use of 22k resistors in place of the original 10k resistors is intended to allow for a broader range of control over the base voltage of the transistors, thereby affecting the operation of the MOSFETs that drive the load. The dual potentiometer serves as a variable resistor that fine-tunes the base voltage, allowing for real-time adjustments to the inverter's performance.

In practical implementation, the circuit should be assembled with attention to the connections between the resistors, potentiometer, transistors, and MOSFETs. The dual potentiometer must be soldered correctly to ensure reliable operation. The testing phase should involve monitoring the output voltage and current while making adjustments to the potentiometer, ensuring that the inverter operates within safe limits. The presence of a series bulb during testing provides a safeguard against excessive current draw that could damage the MOSFETs.

The integrity of the PWM signal at the MOSFET gates is critical for the proper functioning of the inverter. Any irregularities in the waveform, such as missing pulses, should be investigated further, possibly indicating issues within the PWM circuit or the components involved. Adjustments may also be necessary based on the observed performance of the inverter under different loading conditions, with the aim of achieving a stable and efficient operation.

Overall, the circuit modifications and testing procedures outlined are geared towards optimizing the inverter's performance while ensuring component protection and reliability in operation.Just connect 22k fixed resistors across each transistor base and ground and then you may connect the 50K Dual pot leads across these resistors, that should imitate a 10k pot variations quite closely. Hi Swagatam, so just to be clear, you want me to remove the 10K resistors connected to the Base of each Transistor and replace with 22K resistors and connect another two 22K resistors from the Emitters to Ground.

Then connecting the 50K Dual Pot across those connections. Is this correct Swagatam, when I have soldered the Pot into place, I want to make sure I`ve soldered it correctly before I place it into the Inverter. When I power up the circuit, and I turn the Pot, should the voltage at the Output of TR1 & TR2 be going Up or Down in a earlier e-mail I told you that the Dual Pot I had was 50K Ohms, I was mistaken.

It is a 15K ohms Dual Pot. Do I still need the 22K ohms resistors, or a different value Since you say that with my PWM circuit the current consumption of the inverter shoots to a dangerous 14Amps, therefore I just thought, probably we can solve this by reducing the drive voltage to the gates of the mosfets. This can be simply done by controlling the base voltage of the buffer transistors. And that is exactly what we are trying to do by connecting a variable resistor across the base and the ground of each transistor.

As discussed earlier, use lamp and ammeter set-up with the inverter and adjust the 15K pot until the current consumption becomes equal to your square wave design. Hi Swagatam, I performed that test with the headlight, Amp meter and PWM circuit, it was drawing 2. 1 Amps, but whenI tried to adjust the Pot, nothing really happened, the Amps did Not increase or decrease, only when i turned the Pot almost all the way left, it would kill the wave form, literly stopping the inverter, then turning the Pot back to the right the wave form would come back and you can hear the inverter run.

The whole time the Headlight did not change in brightness. My laptop Oscilloscope is only Software, with a homemade probe. Unfortunately most laptop Mic`s Input is in Mono, one channel. So I can`t test both wave forms at the same time to see if there overlapping. Another observation I made, I`ve been studying a few other circuits that are all using the 4017 Chip. I`ve noticed that none of them have those buffer transistors that are used in my original square wave circuit.

What ifI remove them from the circuit altogether. I`ve noticed that in all the other circuits the Clock Input goes directly to the 4017, then out of the two Outputs that they are using, directly to the gate of the mosfet through a small resistor. You may try different configurations taking the help of other circuits but always keep the series bulb connected, it will prevent the mosfets from blowing off if something goes wrong.

Hi Swagatam, I placed 22K resistors across the base and ground of both transistors, this time when I did the Headlight, Ampmeter to Inverter in series Draw test, I got a readingof 1. 80 A, Exactly the same as the Square Wave circuit, itdrew 1. 82A Now that sounds good, but when I checked the Wave form at the Gateof both banks of Mosfets, the wave form on the Gate that is driven by IC2 is corrupt, it is missing a pulse, I`ve sent two screen shots.

The screen shot that is missing a pulse comes from the Gate of the Mosfet driven by IC2 and the other screen shot that is not missing a pulse is comes from the Gate of Mosfet driven by IC1. You will also have to check the waveform at the diode junctions to make sure whether its the fault of the PWM section or is it happening due to the lamp and the base resistor.

Replace the present transformer with a much lower power transformer, say a 12-012/1 Amp transformer, after this you may proceed with your waveform checks and also by connecting smaller loads at the output (like a 10watt 120V lamp) and see the results. Hi Swagatam, I checked the w