Part Number: UC3825
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In reply to Peter Meaney:
In reply to Colin Gillmor:
In reply to takahiko yokota:
You can parallel multiple power stages using the UC3825 - or indeed any controller operating in current mode control (but not Voltage mode control) by connecting their error amplifiers as voltage followers and then connecting their inputs to the output of an error amplifier. This could be an external error amplifier or an error amplifier in one of the power stages. I don't have a diagram of this arrangement specifically for hte UC3825 but the general idea is sketched out in the attached file.
Please let me know if you have any further questions - especially if it is not clear how this method applies to the UC3825. I'm sorry for the short reply but I'm travelling all week on business with little free time.
Thanks for reminding me of this - I had 'lost' the task and was unable to find it.
Anyhow, the customer's option won't work, the two outputs of the IC will 'fight' each other - one pulling up while the other pulls down.
The option with the 'OR' gate is the correct concept but it won't work because the OR gate won't have enough output current to drive the MOSFET properly. (your diagram had a small 'typo' and showed the two OR gate inputs shorted together
The option with the two diodes is the best - and lowest cost - solution. The Vf of the diodes will subtract from the output voltage of the IC but if you use Schottky devices that won't be a problem. Do make sure that the diodes can carry the pulse currents delivered by the IC into the MOSFET.
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