Boosting PWM voltage

Thread Starter

Kimi555

Joined Oct 30, 2020
17
Hi guys,

Just wondering on the easiest yet reliable way to boost PWM output voltage. Im currently using a darlington which is powered from supply while the PIC is powered from a regulator. It is working but im not sure what effect the darlington has on the PWM wave (all i know is it seems to invert the PWM). Anyway maybe there is a tried and tested way to do this?

Thanks
 

ronsimpson

Joined Oct 7, 2019
1,182
A Darlington with the Emitter on ground will invert.
What is the supply voltage for the PIC?
What are you doing with the Collector of the transistor?
Do you have a schematic? more information
 

Ian0

Joined Aug 7, 2020
1,920
How much do you want to boost it? If it's to somewhere between 5V and 18V, then a MOSFET gate driver does the job. See Microchip's MCP1401/MCP1402 depending on whether you want it inverting or non-inverting.
 

Ian0

Joined Aug 7, 2020
1,920
One can drive a logic mosfet directly from a PIC, if the PWM frequency is not to high.
True, but then you have a single-ended output which needs a pull-up resistor and can’t drive any significant load without voltage drop. Use a MCP1401 because it has a push-pull output.
 

jpanhalt

Joined Jan 18, 2008
11,088
??? This is the output circuit for the MCP1402 (source: datasheet):
1604398626501.png

Either one or both mosfets can be driven directly, particularly if the PIC uses 5 V. Complementary mosfet chips in single packages are readily available. I am not saying using such mosfets alone is superior, just an alternative.

Are you arguing that the MCP1401/1402 doesn't work for the TS's purpose?
 

Ian0

Joined Aug 7, 2020
1,920
Don’t quite know his purpose! All he wanted was a PWM with more voltage, and I’m assuming from that he needs a push-pull output because his original PWM would be push-pull. A pair of complementary MOSFETs don’t have any voltage gain.
 

Thread Starter

Kimi555

Joined Oct 30, 2020
17
Great thanks for the information guys. Im using it to control a induction heater as per the below circuit (L- being the PWM). They use a negative PWM signal to pull the FETs low which inverts the PWM duty and as it turns out using a darlington has the same effect. I dont have a scope so am flying blind and after reading a bit about darlington I thought maybe this is not a good way to boost the PWM voltage (slow etc). The one I have is ULN2003AN. The PWM frequency is ~60HZ. I just want to make sure I am using appropriate hardware as opposed to what I had lying around!

Thanks again for the guidance.

1604435750372.png
 

Thread Starter

Kimi555

Joined Oct 30, 2020
17
Just an addition to my last post. I have noticed this morning that the PWM only has an affect on the circuit at the higher duty cycles (above about 80%) would i be correct in thinking this is because at the higher duty the darlington switches more cleanly with the longer low time?
 
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