Bit of a long shot and a very general question. I designed a boost converter circuit with the usual topology. The inductance value was 160 mircroH, capacitance 150 microF, a normal silicon diode and a TIP 31A transistor. The DC supply inputted 10 V and provided an output voltage (measured across the capacitance) of 21 V. As soon as I added any resistance value, the voltage measured across the load was no longer larger than input voltage. A full variation of duty cycles were used for the PWM signal going into the transistors base, but had no effect on boosting the voltage.

A side note, the 555 timer is providing the PWM signal and the variable resistor allows for change with the duty cycle.

In the image the connections aren't quite right regarding the PWM generator, but just know that it did supply the correct signal.

Is there a reason my boost converter works with no resistive load and does not when a resistive load is applied?

 

The '555 oscillator, as drawn, will not work. Trigger and threshold are connected to ground and there is a diode in series with what would otherwise be the timing capacitor.

 

Yeah, sorry I've just updated the description, the circuit diagram regarding the 555 timer is wrong, but in the lab it was correctly built as a timer circuit. My main concern is the boost converter portion of the circuit.

 

Here is what the built circuit looked like.

 

Here is what the built circuit looked like.

C1 can never charge. Blocked by D1.
Did you check what frequency the '555 was running at?

 

The 555 timer was operating in astable mode, frequency 256 Hz. Regarding C1, again I've made a mistake I do apologise, the connection was below D1. I will amend again.

 

Here is the correct circuit, again apologies

 

256 Hz? Are you serious? To use a 150uH inductor, it would need to run in the 100KHz region.

Bob

 

Well being a novice, the method of building the boost converter was to get a boosted voltage and go from there. Towards the end of the project I realised the importance of selecting a correct inductance. By switching the polarity of the inductor and adding blue-tac to both the top and bottom of the seal provided a 75 V output. But what I don't understand is why, even though the inductance was low, the voltage was boosted with no load and then when a resistive load was added the voltage was no longer boosted.

 

Well, looking at your circuit, I doubt that it is running at 256 Hz. More like 30 KHz.

Bob

 

https://www.electronics-tutorials.ws/blog/pulse-width-modulation.html
It's operating in Astable isn't it meaning the frequency is at 256 Hz. I ripped this circuit from the web and it is quoted at providing a 256 Hz PWM signal.

 

This calculator reckons that for 200mA output current with the rest as you have in your circuit you need a 24mH inductor.