Power Converter for 60Hz USA Electric Clock.  Using a 60Hz clock in the UK on 230V 50Hz.

Power Supply.
The 230V input is half wave rectified producing a HT DC supply for the output switching stage,
a capacitive dropper is used to provide a 5V supply for the clock oscillator and dividers.

The capacitive dropper was used as the circuit didn't need to be isolated from the mains, the board
was to be fitted inside the "Rather Large Clock", the capacitors used in this power supply are special
"X" rated parts that are suited to being thrown across the mains!, discharge paths are provided to
reduce the risk of getting a zap from the mains plug pins upon disconnecting the power.

Oscillator and Dividers.
How to provide a stable 60Hz! signal...
Well let's have a look in the component drawers and see what's are there!, I didn't want to
have to buy any parts especially for this project, I wanted to use what was in stock.

I don't remember where the 6.144 MHz oscillator module was scavenged from, (maybe an old
graphics card!) but after considering the division required to get down to 60Hz it looked promising.
Using the divider ic's I had in stock a division by 100 followed by 1024 was chosen.
The programable divider 74HC40103 set to divide by 100 gets the frequency down to 61.44kHz
the 74HC4040 gives further division by 1024 to give 60Hz, with a stability as good as the mains.

Motor Drive.
The high voltage output stage uses transistors rated at 400V, again parts from stock, unfortunately
I didnt have any suitable high voltage PNP types, so an all NPN output stage is used.

The power transistors are driven off and on by the 5V 60Hz signal from the dividers, the top
transistor has a "Bootstrap" capacitor to its base drive to make sure it is fully on when driving
the inductive load of the motor, I found that without this the voltage at the emitter would sag
during the high period of drive, leeding to a bit too much dissipation in the transistor.

The clock motor is placed in a bridge across the HT supply, the capacitors and the inductance of
the motor result in a rounded drive current to the motor, a square wave made the motor run very
warm, this way the motor gets a distorted sinewave drive leading to a quieter and cooler motor.

The Large General Electric Clock is in a workshop in Swindon and keeps very good time.