RE: Solid State Voltage and Current Regulator (fwd)
From: Richard Wayne Wall[SMTP:rwall-at-ix-dot-netcom-dot-com]
Sent: Monday, January 05, 1998 2:48 PM
To: Tesla List
Subject: Re: Solid State Voltage and Current Regulator (fwd)
>>beware that if the transistors fail they will (typically) short, so
>>suddenly burst up to full power - this may not be a good thing.
>>also, you said "dissipates" 3 KW - did you really mean that it will
>>3KW??? I would hope the dissipation is much lower than 3KW.
>The configuration that has been described has a transistor in the
>The transistor acts like a variable resistor! It will indeed
>dissipate a lot of power. That's one
>of the reasons I'm not fond of that approach even though it is very
>simple one to build.
>Some pwm approach would be much better.
A couple of good points. Yes, that's 3.1 kW power dissapation that a
single module can handle, if necessary! These guys are brute force
solid state devices. Not for the faint of heart.
If the current limiting BPT fails (short) then the base drive to the
series pass BPT is depleted and the transistor is shut off. In the
very unlikely event the series pass module fails (shorts) the potential
current in a noncurrent transformer is unlimited. It's also fairly
simple to put a crowbar circuit in to shut down the main circuit if
this unlikely event occurs. Also, note these modules are well
protected with multiple reverse diodes built in and are designed to
control large inductive loads and motors. Right up the Tesla Coiler's
Harri's observation about these series pass transistors are analogous
to large variable resistors is partially correct. Resistor are always
fully on and are incapable of functioning in a cut off mode. These
transistors dissapate virtually no power in the full on mode or cutoff
mode. As they turn on, the power they dissapate is proportional to CE
current through the transistor times the voltage drop across CE. So,
depending on the set current and voltage, power dissapation may vary
widely. All the small solid state voltage regulator devices opporate
with this same series pass configuration. And, current limiting of
large noncurrent limited transformers now employs various inductive,
capacitive and resistive schemes. Often dissapating power in other
Please let us know more about your pwm approach for controlling
voltage, current and driving HV transformers.