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Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Does anyone have any experience with the ka7500 smps controller? Before building my smps I am trying to get a feel for the controller. Right now it is hooked up on my breadboard with the oscillator running at ~700hz, pins 3 and 4 low, pin 13 high, and the comparators left floating. On the output I get a square wave at exactly 50% duty 1.3ms on, 1.3ms off. As I understand the internal diagram , you are supposed to have pin 3 held low until a bad condition occurs and then it is pulled high to disable the output. Pin 4(dead time) is to alter the duty cycle. How is this achieved? I have tried feeding a voltage into the pin so that it compares the oscillator voltage and input, but that does nothing but disable the output. Any help?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The KA7500 is the same as the TL494, so any schematics and data sheets you can find for that will apply.
The last time I used the pin 4 dead time function, I connected the wiper of a 2k pot to pin 4, then connected the track ends to ground and the TL494's onboard 5V reference. Twiddling the pot would then adjust the duty cycle.
If you're not using the error amplifiers, you need to make sure they're disabled.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
yes, i was just reading this . i hooked it up exactly as is shown(same as in this datasheet too). but how do you hook up both the dtc and feedback/comp-input? i have been using a 5k pot with between the 12v rail and gnd(to avoid overloading the rerf) and adjusting it between 0-5 volts. but nothing. what did you do with the feedback when changing dtc?
edit: alright, i solved it- comp input goes to ground, but when i tried it before, there was so much jitter on the long jumper to the pot that it threw me off. plenty of decoupling and shorter wires are key when using this chip.
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ka7500c
