This article documents an implementation of PAROT (Power Amplifier Run On Timer) using Transformerless power supply for PAROT.
This PAROT uses a 10A SSR for 230V mains switching and does not include PTT switching, but space exists for a FOD852 opto coupler for PTT switching.
The immediate application is to control my main station power supply so that if it has been in use, is hot and fans are running, the PAROT provides in this instance a 5min cool down before powering down.
Above is the electronics built on a small piece of Veroboard.
Above is the copper side of the Veroboard. The layout is designed to accomodate another implementation using a small Triac to switch a 230V AC relay. The board has been given a heavy coat of acrylic PCB lacquer to improve voltage withstand.
The PAROT is assembled inside a small die cast aluminium box with stick-on rubber feet.
Above is a view of the interior of the box. A 430V MOV is connected across the SSR output terminals, it is not clear whether the device has internal protection (Chinese product, very brief data). The LED / momentary switch on the right is the only control and indicator for PAROT operation. Note that because of the transformerless power supply, everything inside the box is potentially at mains voltage… a fact that must be kept in mind when working on it. An isolation transformer is a worthwhile tool for working on these type of things.
Above, the exterior of the PAROT.
Above is a thermograph of the PAROT after 15min at 10A load current. The box was 18° before the test, and temperature rise is 3.5°.
Brown out test
The PAROT was connected to a Variac and voltage varied from 265V down with the PAROT on 10A load. The device worked down to 130V at which it dropped the load, but reapplied power to the load when the voltage was raised to 140V. The power supply is quite adequate to supply the current required by the SSR.
A test with a portable receiver and listening on the station receiver did not reveal any significant noise emissions from the PAROT.
Extension to other contexts
This design is for nominal 230Vrms 50Hz AC supply. The main power supply series capacitor must be designed for the voltage and frequency used.
This implementation is configured for 300 second cool down time, no other options are active.
Above is the EEPROM configuration (using Hex Editor Neo's structure viewer).
- Duffy, O. May 2016. Transformerless power supply for PAROT.
- Duffy, O. March 2013. Power Amplifier Run On Timer (PAROT). https://owenduffy.net/module/parot/index.htm.