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I have been trying to build a simple PWM power supply to use a 3.7v battery to drive a small heating element with a DC resistance of about 1 ohm. I have built a slightly modified version of the following LT3759 based circuit:

lt3759

I modified the circuit for an output voltage of 5.0V.

I have no problem getting the expected behavior from the circuit on my scope with a large load, in the kOhm range. When I try to drive the heating element I want, the voltage drops to about 400mV.

I suspected this might be some sort of impedance issue, so I put a simple voltage follower with a mosfet at the output, but this failed to resolve my issue.

Does anyone have any insight as to why this is happening? I am guessing it is something trivial that I am missing due to my lack of background in this area.

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  • \$\begingroup\$ You can use LTSpice tool to verify and tune the circuit, Since its LT part you get models and spice files easily... \$\endgroup\$ – AKR Feb 9 '15 at 5:41
  • \$\begingroup\$ I have the same problem as you, with a low resistance unit, just cannot the right output. Have you figure out what the problem is? \$\endgroup\$ – user73661 May 2 '15 at 0:10
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Your 1 ohm heating element will want 5 amps from a 5 volt supply. That drawing indicates the circuit is only good for 500 mA output with an input voltage less than 8 volts.

If the circuit could deliver the required 5 volts, it would attempt to draw about 6.75 Amps from the 3.7 volt battery. Can the battery deliver that current?

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