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Obsolete Flash


Sea & Sea strobes.


Sea & Sea YS60 circuit diagram.
Traced by László Kalmár

Sea & Sea YS50TTL-II circuit diagram.
Traced by DWK.

Sea & Sea YS50TTL-II circuit diagram.
Traced by László Kalmár

Adding voltage regulation to the YS50TTL-II
by László Kalmár
Referring to the Circuit diagram:
The Sea & Sea YS50 is an example of a strobe to which voltage regulation can be added retrospectively. In the original circuit, the turns ratio of the inverter transformer T1 is chosen to provide a 330V DC output for a battery voltage of 6V. The primary winding of the transformer is however on the outside, and so turns can be removed to increase the turns ratio. To do this, the transformer is de-soldered and removed from the circuit board (carefully) and the insulation tape is removed using a few drops of nail polish remover. Removing 4 turns from the outermost layer (without disturbing the ferrite core) alters the ratio such that 330V DC output is achieved when the battery voltage is 4.8V.

Voltage regulation is applied by stopping the inverter when the output voltage reaches 330V. This is done by shorting the base of the inverter transistor (Q4) to its emitter by means of a P-channel FET Q3. Q3 is controlled by a Schmidt trigger circuit (Q1, Q2), a small amount of hysteresis being applied via feedback resistor R5. Use of a Schmidt trigger ensures that the voltage regulation circuit cannot work in analog mode, i.e., the inverter is either on or off, thereby ensuring that it runs cleanly and efficiently.

Setting up is a matter of starting with the wiper of R2 at the R1 end of its travel. R2 can then be backed-off until 330V DC output is achieved with 6V DC input. Be careful not to allow the HV to exceed 330V by more than 3% at any time during setting up. This may damage C2 or even cause it to explode.

The circuit keeps the voltage across C2 at 330±5V with battery voltages between 4.8 and 6V. It can be built on a small piece of Veroboard (strip-board). The original was built using parts salvaged from an old 19.2 kbps Merlin (British Telecom) modem. The design is tolerant of variation, any similar FETs can be used and there are no critical component values.


Above: Voltage regulator board in situ, showing inverter transformer with its outer insulation and 4 turns removed.

 

Left: Detail of voltage regulator board.

 

Suitable board layout. Component side view. Cuts in the tracks on the underside are indicated by thick black lines. The board should can be somewhat bigger than shown to allow room for a mounting hole.