Rad Hard DC/DC Converters
Proton Rad Hard DC/DC Converters
Rad Hard converters eliminate the use of optocouplers, which are
the primary components that are affected by proton radiation.
In a typical
DC/DC Converter application, there must be galvanic isolation
between the power supply pins and the output pins. The reasons for
this concern safety, noise reduction or circuit operation. In most
applications, the various grounds within a system are ultimately
connected to a single point ground. In other applications, the outputs
of the converter are referenced to a potential different from ground.
MDI offered radiation hardened DC/DC Converters which used an
internal radiation hardened optocoupler for input/output isolation.
Now, in order to
provide an even higher level of radiation resistance, and one that
is less susceptible to unit-to-unit variations in the optocoupler,
the isolation function has been replaced by an amplitude modulated
RF link. This RF link transmits the amplified error signal across
the galvanic isolation barrier through a small transformer. On the
other side of the galvanic barrier, the RF signal is demodulated
and applies the error voltage to the PWM control circuit.
Proton Rad Hard parts to rad hard units with an optocoupler: radiation
resistance is improved since the aging and parametric degradation
of the optocoupler is eliminated. The efficiency of the proton rad
hard converters is slightly lower (1 to 2%), since the output magnetic
modulator consumes slightly more power than the optocoupler and
drive currents throughout the converter have been increased for
additional radiation resistance. Operating life of the proton rad
hard DC/DC Converters, even without radiation, is improved over
the optocoupler units, since there is no LED output degradation
over time as found in the optocoupler type.
magnetic modulator in the proton rad hard DC/DC Converters contains
an RF oscillator, the output noise of the proton rad hard DC/DC
Converters is slightly higher than that of the optocoupler types.
The higher noise is in the form of a very low level
2 MHz signal uncorrelated with the output ripple. The 2 MHz signal
is normally at least 20 dB lower than the output ripple.
response of the proton rad hard DC/DC Converters with that of the
optocoupler types, the load application, load removal and response
to line transients is better in the proton rad hard version. The
reason for this is that the optocouplers vary considerably in initial
current transfer ratio, and also over life and radiation. This means
that the optocoupler units have to be compensated for a much wider
range of conditions than the magnetically isolated proton rad hard
units. The compensation being more conservative, the closed loop
bandwidth of the optocoupler types tends to be approximately half
as much as the bandwidth of the proton rad hard units. Since the
recovery times from transient events is inversely proportional to
bandwidth, the proton rad hard converters have better transient
turn on overshoot of the proton rad hard DC/DC Converters is essentially
non existent because the circuit topology and wider bandwidth.