Hey,
So I made this boost converter based on an mc34063A, but the boost converter output voltage rapidly rises regardless of pot value ( crossed 600V+ ) with no sign of stopping. Where am I wrong? I individually checked the parts to make sure none were faulty... Where am i going wrong here?
datasheet- MC34063A https://www.onsemi.com/pub/Collateral/MC34063A-D.PDF
and
tc4427A
Thanks,
TamjidK
Your signal inverter cannot be driven by the open collector output. It will short the 5V power supply when the collector is off instead of providing a proper LOW.
Smajdalf:
Your signal inverter cannot be driven by the open collector output. It will short the 5V power supply when the collector is off instead of providing a proper LOW.
Is there a way to avoid this? I looked online but couldn't find any simple enough design that basically Outputs High when the input is low and vice versa? the MOSFET driver takes care of the rest...
Try to remove the NPN transistor and use a pull-down resistor instead. A pull up to the PNP base may be needed to increase the turn off speed.
Hi,
How many volts are you trying to get as output?
What is the voltage on the 18650 + input?
What is the output MOSFET rated at?
Have you measured the feedback volts out of Pot1?
Thanks.. Tom.. 
TomGeorge:
Hi,
1.How many volts are you trying to get as output?
2.What is the voltage on the 18650 + input?
3.What is the output MOSFET rated at?
4.Have you measured the feedback volts out of Pot1?Thanks.. Tom..
12V, no more than 1.5 amps at the output.
By 18650 I meant the standard single cell 18650 li-ion battery. which has a nominal voltage of 3.7V and min-max 3V-4.2V.
3.The output mosfet has a maximum drain-source voltage of 60V, although i have seen nothing that indicates that my mosfet is broken, but i can replace it, but i only have one more of these.. so if that ones broken im going to have a problem.
4.Yes, as i said before, I have tested the individual components beforehand. Moreover, as a precaution, i set the trimpot resistance to the values i needed following the formula on the ic's datasheet ( internal reference 1.25V )
Smajdalf:
Try to remove the NPN transistor and use a pull-down resistor instead. A pull up to the PNP base may be needed to increase the turn off speed.
Yes, that wouldve been the simplest solution, but i assumed it wont work because im not sure if this provides "true" ground. The datasheet of the mosfet driver states
Typ max
VIH Logic 1 High Input Voltage 2.4 — — V
VIL Logic 0 Low Input Voltage — — 0.8 V
so basically im not sure if this single transistor configuration can do this atleast.
BTW why you don't use the MC34063 to do the voltage conversion directly? This seems much more complicated than needed.
Smajdalf:
BTW why you don't use the MC34063 to do the voltage conversion directly? This seems much more complicated than needed.
The internal switch of the mc34063A cant handle more than 2A, so at the best-case scenario, that's about 8Watt from the batteries with 100% conversion efficiency. I assumed i would get 60~70% efficiency, So that calls for at least 6 to 7 amperes of current draw.
Although the datasheet has a schematics for usage with external npn transistor, theres no mention of using MOSFETs.
i very much think this is possible, but really cant put my finger on whats okay or whats not.
Hi,
To repeat;
4. Have you measured the feedback volts out of Pot1?
That is the voltage between gnd and the wiper of Pot1 as the output volts goes beyond 600V!!!!!!!
To quote;
So I made this boost converter based on an mc34063A, but the boost converter output voltage rapidly rises regardless of pot value ( crossed 600V+ ) with no sign of stopping.
Try it with 100R across the output, give it a load.
What is the voltage rating of C2, 1000uF?
Can you post a picture of your project so we can see your component layout?
Tom....
PS. Any reason for this project, seeing as you have already used 2 ready made boost converters?
TomGeorge:
Hi,
To repeat;
4. Have you measured the feedback volts out of Pot1?That is the voltage between gnd and the wiper of Pot1 as the output volts goes beyond 600V!!!!!!!
To quote;
Try it with 100R across the output, give it a load.
What is the voltage rating of C2, 1000uF?
Can you post a picture of your project so we can see your component layout?Tom....
PS. Any reason for this project, seeing as you have already used 2 ready made boost converters?
I didnt try it with any load, checking it now.
My project looks pretty crappy and messed up.. but okay, ill post pictures soon.
The capacitor is 16V, one more reason i didnt kill myself with a capacitor charged beyond 600V.
Well, life doesnt go the expected way does it... I first planned to use the XL6009 boost converter, the supplier listed it as 3V input capable, I tried it with 3v, also foolishly without any load, and ultimately discovered that doesnt work under load. Then my plan B was to use a dedicated IC, and also, fml, the only one i could find in my country was this one.. the mc34063A, this problem came up, not enough current capacity, i moved to plan C, use 555 timer, AND THEN AGAIN >.< the only 555 timersi can find are NE555 ones HAVE A MINIMUM VOLTAGE OF 5V!!!!! AGAIN!( think xl6009 ), so back to plan D, make Do with plan B.
which is why i have to do this thing.
Plus, in case you ask, the 3V to 5V is integrated with the charging system, and cant provide enough anyways, aside the fact that the dw01 on it has current limits.
Step up from 4V to 12V with 1.5A output current is quite difficult to build and I think it is nearly impossible on a solderless breadboard. You also need proper (huge) passive components for this: the coil needs to be rated for this current as well as the output capacitor (they need to have a very low ESR).
Since your cap is rated for 16V and the MOSFET for 60V I wonder where you got the 600V value. Maybe you are measuring something wrong.
Hi,
The capacitor is 16V, one more reason i didnt kill myself with a capacitor charged beyond 600V.
The fact the the capacitor is rated at16V does not mean it cannot have 600V applied to it.
If you really are measuring 600V DC, then you have big problems, especially if you are heating wires.
Do you have a scope?
What other projects have you built before?
Any reason for this project, seeing as you have already used 2 ready made boost converters?
Tom...
Smajdalf:
Step up from 4V to 12V with 1.5A output current is quite difficult to build and I think it is nearly impossible on a solderless breadboard. You also need proper (huge) passive components for this: the coil needs to be rated for this current as well as the output capacitor (they need to have a very low ESR).Since your cap is rated for 16V and the MOSFET for 60V I wonder where you got the 600V value. Maybe you are measuring something wrong.
18 gauge is plenty big in my opinion, for the inductor.. plus im not doing this on a solder less breadboard, perfboard with 16 gauge wires for better connectivity.
I had my multimeter connected everytime, my guess would be i pulled the plug everytime before anything got the chance to explode.
TomGeorge:
Hi,
The fact the the capacitor is rated at16V does not mean it cannot have 600V applied to it.
If you really are measuring 600V DC, then you have big problems, especially if you are heating wires.Do you have a scope?
What other projects have you built before?
Any reason for this project, seeing as you have already used 2 ready made boost converters?Tom...
I meant the capacitor cant be stable and hold that much voltage for long before destroying itself..
Sadly, no , i dont have a scope.
some other projects... Tesla coils, slayer exciters, rc controllers, high power led drivers, 2 2HP pump controllers and a few more here and there. anything that seems fun. why do you ask though??
I believe i answered your question albiet a bit vague.
kaseftamjid:
Well, life doesnt go the expected way does it... I first planned to use the XL6009 boost converter, the supplier listed it as 3V input capable, I tried it with 3v, also foolishly without any load, and ultimately discovered that doesnt work under load. Then my plan B was to use a dedicated IC, and also, fml, the only one i could find in my country was this one.. the mc34063A, this problem came up, not enough current capacity, i moved to plan C, use 555 timer, AND THEN AGAIN >.< the only 555 timersi can find are NE555 ones HAVE A MINIMUM VOLTAGE OF 5V!!!!! AGAIN!( think xl6009 ), so back to plan D, make Do with plan B.which is why i have to do this thing.
Plus, in case you ask, the 3V to 5V is integrated with the charging system, and cant provide enough anyways, aside the fact that the dw01 on it has current limits.
Hi,
If you look at the mc34063A datasheets, you will se that they have a recommended PCB layout.
Because of the currents involved and the frequencies and the fact that most are squarewave, the layout of the circuit is critical to proper operation.
If yours is basically long wires and plug type connections, then you are pushing uphill for a result.
SMPS are hard to design and make from prototype, and the fact you do not have a scope to check your circuit operation will hamper your results.
Tom...
TomGeorge:
Hi,
If you look at the mc34063A datasheets, you will se that they have a recommended PCB layout.
Because of the currents involved and the frequencies and the fact that most are squarewave, the layout of the circuit is critical to proper operation.
If yours is basically long wires and plug type connections, then you are pushing uphill for a result.SMPS are hard to design and make from prototype, and the fact you do not have a scope to check your circuit operation will hamper your results.
Tom...
Okay, so reliability is a definite issue when dealing with long wires. I tried to reduce this by separating the actual boost converter part (inductor-MOSFET-capacitor-diode, basically the things with high current passing through), So the only "long" wire is the 4cm long wire that connects to the gate of the mosfet from the mosfet driver. So i hardly doubt that the long wire is a issue right now.
Even so, could you confidently say that long wires are causing this problem for me? My ultimate goal is to make a pretty pcb according to spec to bring everything in one place, but to do that, i have to make this boost converter part work first.
Judging from the question before, I may be a beginner, but im not a complete noob to make silly mistakes that i think is right, like not using correct traces/wires for high current applications.
Hi,
This "inverter" will not properly invert, how do you think it works?
Tom...
Hi,
If we simplify your inverter, you do not have either of the BJTs biased properly.
Tom...
