I need a power supply that can deliver stable 370 V DC voltage, while load resistance is variable.
Average load current(assuming stable 370 V supply) is 200 mA, however it may rise to 400 mA. Input voltage(DC) is 40 – 60 V higher than 370 V, but it's unstable.
I was expecting that I would simply buy something like LM317, but rated for 370V and 400mA. It quickly turned out that nobody sells such things.
Closest to what I need was this stabilizer: Microchip LR8K4-G, 1.2 → 440 V Linear Voltage Regulator, 30mA, 1-Channel, Adjustable, ±5%.
It meets my voltage requirements, but it can only handle 30 mA.
This fragment from its datasheet caught my attention:
The output voltage can be adjusted by means
of two external resistors, R1 and R2, as shown in the
typical application circuits. LR8 regulates the voltage
difference between VOUT and ADJ pins to a nominal
value of 1.20V. The 1.20V is amplified by the external
resistor ratio R1 and R2.
So if we can just amplify the voltage difference, then perhaps there is a way to use lower voltage stabilizers for higher voltage? Can somebody point me in right direction?
Best Answer
How about follow the LR8 with an emitter follower?
simulate this circuit – Schematic created using CircuitLab
On the one hand, the Q1 VBE is not well defined, but on the other, any error is negligible compared to the errors there will be in setting the LR8 output voltage.
This arrangement is not current limited, other than Q1 beta times LR8 limit, but it would be straightforward to add a few more components to make it so