13V/2A PSU For Handheld Rigs

This compact 13-V/2-A power supply for ham radio rigs and other VHF/UHF portable PMRs
is based on the STR2012/13 voltage regulator IC from Sanken Electric
Co. Many power supplies for handheld amateur radio rigs are based on the
LM317, LM350 or even the good old LM723. Unfortunately, these
regulators are invariably associated with a fair number of external
components, while we should also consider design factors like total
power dissipation and input voltage range. The STR
is a hybrid power IC containing a switch-mode power supply. It supplies
a fixed output voltage and accepts relatively high input voltages.

Another advantage is its relatively high power dissipation rating. The 5-pin STR
is available for 5.1 V, 12 V, 13 V, 15 V and 24 V at an output current
rating of 2 A. Here, the STR2012 and STR2013 are suggested for output
voltages of 12 V or 13 V respectively. The normal operating voltage of
most handhelds being between 12.6 V and 13.8 V, the STR1303 will be the
preferred device in most cases. A high-speed crowbar circuit is added to
the regulator output. Thyristor Th1 (a TIC106 or 2N4442) is triggered
when the output voltage rises above the zener voltage of D2, that is, 15
volts (approximately). When this happens, the thyristor short-circuits
the supply output, protecting the radio against over voltage and blowing
fuse F1.


Circuit diagram

Diode D1 acts as a reverse polarity protection, also in combination with fuse F1. To allow for its dissipated heat, the STR
regulator should be mounted on a heatsink. Efficiency will be around
80%, with ripple rejection at a comfortable 45 dB. The raw input voltage
to the regulator should be in the range 18 to 35 V. The coil, L1, may
be selected from the range produced by New-port. The type 1430430 is
suggested. If difficult to obtain, then an ordinary triac suppressor
type may be used instead.

Note, however, that the inductance of these coils is usually just
100µH, so you have to count the number of turns and add another 0.7
times that number to arrive at about 300 µH. Finally, keep the wire
between pin 3 of the STR and ground as short
as possible, and connect at least the negative terminals of C1 and C3 to
this point to give a ‘star’ type ground connection.

Sorry, comments are closed!