It should work but you are leaving out some parts:
- Deadtime setting resistor
- Low current consumption when off, that's achieved by adding a PNP transistor and switching VCC to +12V with the remote. Rather than for permanent turn-off, the shutdown pin is better suited, for example, to implement pulse by pulse current limiting with an external current sense element and a comparator.
- Deadtime setting resistor
- Low current consumption when off, that's achieved by adding a PNP transistor and switching VCC to +12V with the remote. Rather than for permanent turn-off, the shutdown pin is better suited, for example, to implement pulse by pulse current limiting with an external current sense element and a comparator.
I think I will add a dead time resistor just to be safe, but with non it still does have a bit of dead time... I am not sure about the NPN turn on, is it something like I have put in the new schematic? Normally I would just use a relay but a NPN would be cheaper and smaller.
Attachments
Fishy-
The PNP Eva suggests for the turn-off action is to minimize the '3525's quiescent current, which is also its operating current, about 20-25mA. If your ckt is battery powered, this is critical.
For your deadtime resistor, 100ohms should do nicely. I noticed you rea running this WOT (wide-open throttle). Do you plan to run it in true PWM regulating fashion?
Steve
The PNP Eva suggests for the turn-off action is to minimize the '3525's quiescent current, which is also its operating current, about 20-25mA. If your ckt is battery powered, this is critical.
For your deadtime resistor, 100ohms should do nicely. I noticed you rea running this WOT (wide-open throttle). Do you plan to run it in true PWM regulating fashion?
Steve
I am going to be using this SMPS to power a Tripath based amp and they seem to work very well with an unregulated power supply so I am thinking of running it WOT. Unless there is a good reason to make it regulated? I could try something like bellow from Rod Elliott's web page. Maybe just connect the output of the transformer through a pot back to the inverting input?
An externally hosted image should be here but it was not working when we last tested it.
thefish said:
Fish-
Saw two other things: 1) You implemented an NPN in series between the Vc&Vcc pins and +12V. Your Collector and Emitter pins are reversed. This would work, BUT, in order to fully turn on the NPN, you would need to appluy a voltage at its base that is higher than whast will be at its Collector when it is on. That is, its voltage will have to be higher than the +12V powering the '3525. Unless you have a charge pump generating this higher voltage (say, ~16-18V), your NPN will never fully turn on, impeding the 3525's ability to start properly; and 2) This NPN should be a PNP. Eva suggests using a PNP here, because to turn it on, you simply need to ground the base, since the PNP is referenced at +Vcc, and not ground. To do this, simply place two resistors, say 10KW in series from the PNP's base to ground, and take an SPST switch going from the junction of these two 10KW resistors and run it to +Vcc.
When the switch is closed, the PNP will be biased off, and the SG3525 will be shutdown. When you open the switch, the PNP will bias on hard, thus powering up the '3525 allowing it to start properly.
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